tag:blogger.com,1999:blog-83710512024-03-05T09:00:47.273-08:00MoosteriaBecause you never need to get moosterical.Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.comBlogger163125tag:blogger.com,1999:blog-8371051.post-74164960287190000692023-12-26T13:17:00.000-08:002023-12-26T13:20:44.857-08:00At last, a 3D printed watch<p>I've recently completed the 3D printed watch with tourbillon, designed by Christoph Laimer and published on <a href="https://www.thingiverse.com/thing:1249221">Thingiverse in 2016</a>. Here it is in operation:</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/JxfDZEvB9UY" width="320" youtube-src-id="JxfDZEvB9UY"></iframe></div><p><br /></p><p>You might notice that it does not remotely keep time: a minute on the watch is only about 43 seconds in real time. I'll say more about that later. A few more pictures:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhtzuIDPpVLhHtWgbf9ZJfz5Ktmd51lvFDnyP2-Hm8D912kPY3YC1A8hz0U-RuH9leNrwQZrrSAtNJajnwi4UoXCChBB0wH6sDyLB-1B-sFkh6s0Q31sAu2vv_m2ZplTNRNqlYV1MkA7Tv5iTvQQTR9m_dV_pYa5lbAYy8o4ttqNV3GlBNJkBHW/s4080/PXL_20231226_203824639.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhtzuIDPpVLhHtWgbf9ZJfz5Ktmd51lvFDnyP2-Hm8D912kPY3YC1A8hz0U-RuH9leNrwQZrrSAtNJajnwi4UoXCChBB0wH6sDyLB-1B-sFkh6s0Q31sAu2vv_m2ZplTNRNqlYV1MkA7Tv5iTvQQTR9m_dV_pYa5lbAYy8o4ttqNV3GlBNJkBHW/s320/PXL_20231226_203824639.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRMn3LeZNfJiJSK7cJKWyANaMQQCLYgb7j-eaVJyiVRZesrzmonn1uovSo_uSfJ2UZD-r4pbRVxLONTsa2-ToAXZBGh3A2tQLysi4poKZG6NK9-siTOb8P0-ATY778WbDHN0l3-ARZy2RkJXaJ-p_tz7e5_C0gyXwrKxKs-TbplTQUu4L0cDlo/s4080/PXL_20231226_203831305.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRMn3LeZNfJiJSK7cJKWyANaMQQCLYgb7j-eaVJyiVRZesrzmonn1uovSo_uSfJ2UZD-r4pbRVxLONTsa2-ToAXZBGh3A2tQLysi4poKZG6NK9-siTOb8P0-ATY778WbDHN0l3-ARZy2RkJXaJ-p_tz7e5_C0gyXwrKxKs-TbplTQUu4L0cDlo/s320/PXL_20231226_203831305.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijqHyDrsIuOGvnMk2We2M4snlUYp9VMQTD_rxJq2m4SIC-Jk4fCvUub0_asZgerdrvhDL9NQZsoOE97SLJ48grLuzo6g0TfvNH8kqUkqqX1v3KwWfCkUVqlW6lrYbvAQIwox-0uzU0lUE7IripjXX0qX_3MBUo8z1ncNZTsCMMk_tNYkYCACMd/s4080/PXL_20231226_203839207.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijqHyDrsIuOGvnMk2We2M4snlUYp9VMQTD_rxJq2m4SIC-Jk4fCvUub0_asZgerdrvhDL9NQZsoOE97SLJ48grLuzo6g0TfvNH8kqUkqqX1v3KwWfCkUVqlW6lrYbvAQIwox-0uzU0lUE7IripjXX0qX_3MBUo8z1ncNZTsCMMk_tNYkYCACMd/s320/PXL_20231226_203839207.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjCU8TQQdLC3jR4nZ86vCimtyR86Gx1vYnq0M6N3tb6V1j5QWifSafFe1C1mQzUE-IE1HIuzPeV__xK7Wsjm1wWe-BrPLdWg4fxmu0ZKsnJs40guWNnIuhmt7gE-Xl5W2z0UqhM9Azt1B-CIricUtEBjnj1BSzTDCCNVBd4R2unqzOFuxpeS7yD/s4080/PXL_20231226_203851226.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjCU8TQQdLC3jR4nZ86vCimtyR86Gx1vYnq0M6N3tb6V1j5QWifSafFe1C1mQzUE-IE1HIuzPeV__xK7Wsjm1wWe-BrPLdWg4fxmu0ZKsnJs40guWNnIuhmt7gE-Xl5W2z0UqhM9Azt1B-CIricUtEBjnj1BSzTDCCNVBd4R2unqzOFuxpeS7yD/s320/PXL_20231226_203851226.jpg" width="320" /></a></div><p>In brief, the watch works like this. There is a mainspring in the base, which drives the minute train. The minute train is linked to the tourbillon, which locks and unlocks it and so provides the timing. The minute train drives the bronze (greenish) ring gear. Another gear takes the movement from this ring gear into the hour train, which ends up driving the gold ring gear.</p><p>I got my first 3D printer in mid-2015, and when this design came out in January 2016 I decided to give it a go. It completely failed to run, and I set it aside. This is not a surprising outcome. The printer was not very accurate, and I had no idea how to debug clocks and watches or even really much understanding of how they work. Time has passed, and now I have a Prusa MK4. It much more precise than my first printer, and also a lot faster. A consequence of the speed is that I am willing to print at much finer layer heights than before. On my first printer, I was probably using 0.3mm for large parts and 0.2mm for smaller ones. With the MK4, I nearly always use 0.15mm without worrying about how long the prints will take.</p><p>On the debugging side, I now have a better understanding of how clocks and watches work, and this helps in building up the mechanism in stages and do partial tests. The tourbillon itself is a self contained unit and I first tested it in isolation. Then I checked that the minutes train worked smoothly, separate from the tourbillon, then the minutes and hours trains together, and finally the whole mechanism.</p><p>Most of the parts are from the original design. The tourbillon spring is the medium strength one from <i><a href="https://www.thingiverse.com/thing:3647921">A flight of hairsprings</a>.</i> I used the <a href="https://www.thingiverse.com/thing:3642038">Massey pin</a> in the balance wheel mechanism. It makes the balance wheel less prone to jam against the fork. The bridge on the top is modified from the logo-less version from the <a href="https://www.thingiverse.com/thing:1348754">torque modification</a> of the design. I decided not to use the hands from the original design as they don't attach very well, and instead printed the black notch you can see above directly into the ring gears.</p><p>Now to why the timing is off. When I first put the tourbillon together, I found that it would seize. The reason for this is that the balance wheel was swinging a long way on each tick. While it was at the ends of its movement, the fork could flop around. When the balance wheel swung back, the fork might not be in the right place for the balance pin to engage with it and everything locked up. Using a stiffer spring limits how far the balance wheel swings and so avoids this problem. However, it means the timing is no longer right. For a real timepiece, this would be an issue. But in my case, I intended it more as an objet d'art: something to look at. It isn't really a practical clock, as you can't tune the timing or even set the hands. If it ticks at the wrong rate, that's OK.</p><p>I modified a few of the parts. Many interior holes were too small. For the ratchet and ratchet bushing (check the thingiverse page if you want to know which parts these are), I slightly opened them up by editing the STLs in blender. For all of the gears in the minutes and hours trains, I could have drilled out the holes. Instead, what I decided to do was to modify them as follows. All of these gears run on 2mm arbors, so I made the axis hole slightly larger than this for the 2mm or so at each face of the gear (in Blender, again). The rest of the axis hole I made 2.4mm diameter. This means that when I drilled out the holes, I only needed to cut through the 2mm part at each end, so there is not much chance of the drill going askew. The rest of the interior of the axis hole does not touch the arbor, thus reducing friction. Steve Peterson uses this in his clocks, and I've mentioned it in a previous post.</p><p>The teeth on most of the gears are tiny, only about 1.5mm from tip to base. You need accurate printing followed by a close visual examination for any blobs or wisps of filament for them to work smoothly.</p><p>The filaments are Flashforge burnt titanium PLA for the body, gold and bronze silk PLA for the gears and moving parts, and PETG for the main spring. The burnt titanium filament looks very nice, but is not so good to work with. You get a lot of stringing and blobs, and the printed surfaces are slightly rough. The ring gears have a large contact area, so you really need something smooth and with low friction. Silk PLA is ideal for this.</p><p>The design also calls for a rather bizarre range of small screw sizes. I think many of these could be replaced with more standard sizes (or at least to use one or two sizes throughout) with minor design changes. I didn't try this, though it's noteworthy that the design included the original CAD model in Fusion 360 format, making such modifications easier.</p><p>How long will it run? From a full winding, I can get 20-25 minutes. I expect this will decrease over time as the mainspring weakens. Here is a 10x timelapse starting with a fully wound spring and letting it go until it stopped. With a nudge it will run for another minute or two.</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/L-dSPLk5sow" width="320" youtube-src-id="L-dSPLk5sow"></iframe></div><p><br /></p><p>And also a look at the mechanism in slow motion:</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/KWUN63oEuds" width="320" youtube-src-id="KWUN63oEuds"></iframe></div><p><br /></p><p>This is a remarkable design by M. Laimer (aka TheGoofy). It was one of the first 3D printed timepiece designs and it outclasses many more recent designs in the care and thought that went into it as well as the attention to its visual appearance. I would definitely rate it higher than, for example, the <a href="https://www.myminifactory.com/object/3d-print-tourbillon-mechanica-tourbillon-escapement-mechanical-clock-assembly-guide-pdf-in-description-124938">Tourbillon Mechanica</a>, which just looks messy to me, or the many published tourbillon design which just don't run well. Very nice.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-49176199400076832902023-02-12T17:54:00.000-08:002023-02-12T17:54:13.037-08:00Tips and Tricks For Printing Small GearsIt is sometimes difficult to print small gears. Typical problems are teeth pulling up or distorting or simply the whole thing coming loose and sticking to the nozzle. I don't believe there is any universal solution to this, so here are a few tactical things you can do. Obviously start by making sure that your printer is well calibrated, the print surface and nozzle are clean, and that the bed is levelled. I usually clean the nozzle by heating it to just under the print temperature then removing any stuck on filament by lightly brushing it with a brass wire brush. It helps to put a mirror on the print bed so you can see what you are doing. I have a concave shaving mirror that also magnifies. My Prusa MK3S is set up for levelling using a slight modification together with an associated process known as "<a href="https://github.com/PrusaOwners/prusaowners/blob/master/Bed_Leveling_without_Wave_Springs.md">bed levelling without wave springs</a>" (it's a misleading name reflecting the history of how the author of the process got there), and if you put in the time with this you can get a very accurately levelled bed.<div><br /></div><div>The problem with small gears is that you can get small segments in the teeth which result in a lot of nozzle moves and retractions. Due to the viscosity of the filament, the move may pull the feature it has just printed off the print surface or plow through a small feature which is isolated from other features and so doesn't have much attachment area. Generally once you are past the first layer, things will go OK. You might get some stringing or blobs, but you can fix these up when the print is complete.</div><div><br /></div><div>A first thing you can do is examine the features in the slicer preview and adjust settings to try to avoid such features. For example if you see something like the small triangles and dots in this example, you may be in for a problem:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjiSTHmcxGsmf5IBIjNzMggt0XW0_CmeiYeejjj41_lF_YxV1puR6UJQwzcEOpMbF-rbiNsQ42hQArWWo-NFSBIyt74f_8dA11uhgdHq8LA-DKq-3rSBTPuYQ-60810L_bDtRkPYItP-sJYg5J5eXJ8053o7DhBEcqGdcXWbwyskJTjz1GNA/s552/capture_001_12022023_165638.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="342" data-original-width="552" height="198" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjiSTHmcxGsmf5IBIjNzMggt0XW0_CmeiYeejjj41_lF_YxV1puR6UJQwzcEOpMbF-rbiNsQ42hQArWWo-NFSBIyt74f_8dA11uhgdHq8LA-DKq-3rSBTPuYQ-60810L_bDtRkPYItP-sJYg5J5eXJ8053o7DhBEcqGdcXWbwyskJTjz1GNA/s320/capture_001_12022023_165638.jpg" width="320" /></a></div><br /><div><br /></div><div>There are several parameter changes which may help. It's not possible to say that any of them will definitely improve the slicing. The best thing is try them, look at the result and see if it appears better:</div><div><ul style="text-align: left;"><li>increase or decrease the number of perimeters. Stick to a minimum of 2. More perimeters give you greater strength and rigidity. If the gear doesn't take much load (for example, the gear train from minutes to hours) then 2 will be strong enough.</li><li>reduce or turn off elephant's foot compensation. It makes the first layer smaller, so making it more prone to these small features. If your printer is well-calibrated, you may not need it anyway.</li><li>switch between the Arachne and classic slicing algorithms. Sometimes one just does better than the other.</li></ul><div>If you have access to the model you might also be able to tweak it, but that's a bigger task and doesn't always help.</div></div><div><br /></div><div>Another setting that can be useful is external perimeters first. This won't change the slicing, but guarantees that you have a single solid outline for the remaining tracks to stick to.</div><div><br /></div><div><br /></div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-52833541504644568572022-11-12T15:29:00.000-08:002022-11-12T15:29:26.318-08:00Last notes on the clock design<p>It's been a while since I wrote anything more about my prototype clock. I haven't been working on it much.</p><p>There are a couple of changes since the last version. I reorganized the orientation of the gears to space them out a bit, so that there is less chance of them rubbing. I also replaced the previous ratchet with a gravity one. The original ratchet used very thing springy pawls which had a tendency to break off. I replaced this with an arrangement similar to the one used in <a href="http://moosteria.blogspot.com/2022/03/favres-clock-24.html">Favre's clock 24</a>, in which the pawls simply drop into place as the weight drum turns.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiWzinxL8uanJ9av-16KR73UvLZ7MGU8hXZ3In2l_xjzjeuf4uU0IzJNJ3_ygaQOktfJoS_suH8xRzRwLWaaA2JnmL8xr0-rUzN2E_iUgqPUu1pG72p_2qLiBr_wn5Z_bElqibPwA6WRIMHEau9J6sXag2wHdvJtJZYKtJUJ_hIR3HY3Xt-vg/s4080/PXL_20221112_231056054.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiWzinxL8uanJ9av-16KR73UvLZ7MGU8hXZ3In2l_xjzjeuf4uU0IzJNJ3_ygaQOktfJoS_suH8xRzRwLWaaA2JnmL8xr0-rUzN2E_iUgqPUu1pG72p_2qLiBr_wn5Z_bElqibPwA6WRIMHEau9J6sXag2wHdvJtJZYKtJUJ_hIR3HY3Xt-vg/s320/PXL_20221112_231056054.jpg" width="320" /></a></div><br /><p><br /></p><p>I finally got a working seconds hand. In earlier designs, there is a gear that turns once per minute, and this can either be mounted on a non-moving arbor, or attached to an arbor which then also turns the seconds hand. In most cases, as soon as I configured it the second way, the clock stopped working reliably. I believe now that the reason is friction between the seconds arbor and the minute "tube", which surrounds it. For a number of the gears, there is a long tube, either to bring out the motion to the front of the clock (for the minutes and hours hands), or to provide a bit of stability and stop the gear tilting. Like several of the gears seen here:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgoey-dOpVersfADqFZDVsOw6r5fqWYjZhPxaKfEALzaasIHuwU7WtQ_W_-LkrC6tyduKCheyupXaooBVroPTOHa-F3gVMzUUUk63xc96se4B2vQvxV9nR11MBVEQNyONmcBRYSQF8q12YQKXxIkG0oxFVb1jLhwLcaWO8a3N4gqwe0tUU1oQ/s4080/PXL_20221112_231659284.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgoey-dOpVersfADqFZDVsOw6r5fqWYjZhPxaKfEALzaasIHuwU7WtQ_W_-LkrC6tyduKCheyupXaooBVroPTOHa-F3gVMzUUUk63xc96se4B2vQvxV9nR11MBVEQNyONmcBRYSQF8q12YQKXxIkG0oxFVb1jLhwLcaWO8a3N4gqwe0tUU1oQ/s320/PXL_20221112_231659284.jpg" width="241" /></a></div><p><br /></p><p>Doing it this way means there is a lot of contact area between the tube and whatever arbor or runs on. I changed this so that in such cases, the tube opens up inside, so that only the very ends have an inner diameter close to that or the arbor. This made a huge difference in the amount of friction, and the seconds hand now runs reliably.</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/7SV4zdHatMM" width="320" youtube-src-id="7SV4zdHatMM"></iframe></div><p>The biggest remaining flaw is the short run time, as I discussed in a previous post. To increase it, I would need to change the diameter of the weight drum or the ratio of the gearing between the ratchet and the minutes gear. But I think I am done with this prototype and won't carry it through to a more fleshed out design. I've learned a lot from it.</p><p>One last thing which interests me is replacing the weight with a remontoire like the one used in the <a href="http://moosteria.blogspot.com/2022/05/swingtime.html">swingtime clock</a>. To try this, I removed the weight drum an ratchet and just attached a small amount of weight to the gear between the seconds and minutes. You really don't need much weight for it to work:</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/flYteeXDnR4" width="320" youtube-src-id="flYteeXDnR4"></iframe></div><br /><p>Two binder clips are enough. If you are lucky, it will work with one.</p><p><br /></p><p><br /></p><p></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-46264387859823614302022-08-25T15:08:00.003-07:002022-08-25T15:08:38.674-07:00Last experiments with prototype #4<p>For a last round of experiments on prototype 4, I looked at the effect of the weight and drum size. I had been fixing the seconds wheel to its arbor with a set screw. I think this still resulted in extra friction, either from constraining the meshing with the other gears, or (more likely) because of friction between the seconds arbor and the minute tube. For the next experiments, I removed the set screw. The second arbor (and hand) no longer turn, of course, but the friction is significantly less.</p><p>How does the weight affect the running of the clock? I tried different weights, and in each case measured the swing of the pendulum against a ruler. Some minor trigonometry turns this into the swing in degrees, each side of the center. Here's a graph of how things change, showing the angle against the weight in grammes. The values are approximate:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4I3_w0x967780C0DyxDFoHaZ_mxnJcojwCgHM21m1tlMxDJDNLoLP2ie6oryoiWVfZjFUdnSBQQelp4ZCYSEKqJOh4OvFUJgFqRmVX-hpiOIv-Stl2qjpaQVct77H6bgHhtjptmnQonH0wFtTmE3BCl8lc0kHq2mdFwP3lUkPSm1xumkp7g/s581/capture_001_23082022_200116.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="358" data-original-width="581" height="394" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4I3_w0x967780C0DyxDFoHaZ_mxnJcojwCgHM21m1tlMxDJDNLoLP2ie6oryoiWVfZjFUdnSBQQelp4ZCYSEKqJOh4OvFUJgFqRmVX-hpiOIv-Stl2qjpaQVct77H6bgHhtjptmnQonH0wFtTmE3BCl8lc0kHq2mdFwP3lUkPSm1xumkp7g/w640-h394/capture_001_23082022_200116.jpg" width="640" /></a></div><br />Two things are noticeable here. First, in this low friction configuration, you can reduce the weight to a really low value. It would still just about run with only 160g, though at this level any slight upset (such as a strong draft of air) could stop it. Second, it's really apparent that a small relative increase in the weight matters a lot more for small weights than for larger ones: the relationship is not linear.<p></p><p>I measured the the weight to drop at about 17.6 cm/hour. The drum is 50mm in diameter, so you expect this to be more like 15.7 cm/hour. I haven't adjust the pendulum length, and I estimate the clock is running about 10% fast, so from it's point of view, it is 17.6cm per 66 minutes, which is 16.0 cm/hr, closer to what it should be. At this rate, the clock would run for 10 hours on a 1.6m (5 foot) drop.</p><p>Next, I swapped out the weight drum for one with half the diameter. Now we would expect 7.85 cm/hr. The measured value was 9.4 cm/hr, or after correcting for the clock running fast 8.5 cm/hr. It's a bigger discrepancy than before; I'm not sure why. This would give a run time of a little under 19 hours. The minimum weight in this case was around 400g. Even with my larger 1100g weight, the running was a little flaky, and this proved to be that minute wheel was sliding backwards on it arbor and sometimes interfering with the escape wheel. As I've iterated on the design, I've been using slacker tolerances on the spacers, and I think I've taken it too far.</p><p>Finally I did a crude version of doubling by looping the weight cord through the top of the weight and clipping the end of it to the frame. It runs, though a little weakly at 1100g, giving 4.8 cm/hr. After the 10% correction, this would run for 37 hours on a 1.6m drop, which is starting to look good.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh03u37bxALqE3pivoMY6LY1cMfHQRrLXaEeuN_DFxG20kZLIqK8zgw5A1f09eWlp76MrF88YWStDQcEyp9ZKzZNdLWXdKuFXghtuzqFZoSux9OHFyzTRVvfbuPg_KemuO7mU9ADYKUftVA3rNTAn_cxx944fRVDI9pfDOQKt8TPrCoYTkHqg/s4080/PXL_20220824_033800990.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh03u37bxALqE3pivoMY6LY1cMfHQRrLXaEeuN_DFxG20kZLIqK8zgw5A1f09eWlp76MrF88YWStDQcEyp9ZKzZNdLWXdKuFXghtuzqFZoSux9OHFyzTRVvfbuPg_KemuO7mU9ADYKUftVA3rNTAn_cxx944fRVDI9pfDOQKt8TPrCoYTkHqg/s320/PXL_20220824_033800990.jpg" width="241" /></a></div><p>The smallest weight I tried was around 700g, and it ran better with this than I expected.</p><p>I wanted to try using a reduction gear from the weight to the minute wheel, but the frame design doesn't allow enough space for anything other than 1:1.</p><p><b>What next?</b></p><p>This is as far as I intend to take prototype 4. I have a number of ideas for the next version:</p><p></p><ol style="text-align: left;"><li>Change to cycloidal gears. There is some argument that they have lower friction (<a href="http://www.bobinchak.com/watchmaking/2018/5/30/tooth-profiles">ref 1</a>, <a href="https://www.csparks.com/watchmaking/CycloidalGears/index.jxl">ref 2</a>), though I think I have seen this disputed. In any case, redesign the gears so that there is more clearance.</li><li>Change the geometry by flipping G1 to put the escape part at the front and the pinion (gear) at the back. Then G2 can be flipped as well. This may help reduce the change of G3 running into the G2 hub.</li><li>Make a fixed position for the pendulum. It still needs to be movable, to set the beat, but the experiments I did on its horizontal position show that it doesn't matter.</li><li>Stronger clicks in the ratchet. One broke off.</li><li>Redesign the escape wheel teeth. This goes with the previous one. They need to be designed to that the slice better. Currently both of them have odd profiles due to the slicer switching the number of perimeters at the narrow points.</li><li>Make the two intermediate wheels, G3 and G5, smaller, by changing the gear ratios around. The point of this is so that the pillars between the front and back of the clock can be moved to make more space for different ratios in the winding gear. Alternatively make pillars which are curved to allow extra space.</li><li>Consider changing the period of the pendulum, and the number of teeth on the escapement gear and the seconds wheel so that they are not commensurate (i.e. don't have prime factors in common). This reduces the risk of a specific pair of gear teeth being a problem.</li><li>Change the seconds, minutes and hours arrangement that end up at the hands. In prototype 4, the seconds arbor is a 3mm rod, the minutes uses a brass 4mm tube, and the hours uses a printed tube as part of the gear. I'm considering an arrangement where there is a 3mm arbor (or smaller) rigidly fixed into the frame, and each of the seconds, minutes and hours gears has a printed tube, nested on the arbor. It will take more space but might overcome the extra friction I think I saw when the seconds wheel was rigidly fixed to the arbor. Other options might work here.</li><li>Make the spacers have stricter tolerances. You want some endshake on each gear, but they have become too slack as I've made the tolerances gradually looser.</li></ol><p></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-63580736020916327452022-08-21T15:08:00.003-07:002022-08-21T17:32:10.889-07:00Clock prototype #4 again: a problem really solved<p>After my optimism about prototype #4, I reassembled it to make some minor tweaks, and found it was back to stalling. Something I noticed was that the tick got louder and quieter, and this was happening on a 60 second cycle. So that made it pretty clear that something was causing friction in one of the gears with this period, either the escapement wheel or the seconds wheel, or there was a problem in the interaction between them. The clock didn't always stall then the tick got weak, but eventually due to some random factor there would be too little energy to keep the pendulum going. To try to work out the cause, I marked a reference position on both gears, and then moved the position of one relative to the other. I could see that when the clock stalled, the second gear was always in the same position, but the position of the escape wheel didn't matter. The second gear is held on the seconds arbor with a set screw, and the position of this suggested that it displaced the second gear slightly towards the escape wheel, corresponding to the lowest energy, highest friction position. Some clock designs prefer to make the gear tight on the arbor. I don't do this, as it makes it hard to adjust the gear position, and over time it may start to slip. However, with the tolerance issues on the gears I mentioned in the previous post, it was enough to make the gears too tight. I proved this by removing the set screw and seeing that the clock ran well, though of course the seconds hand then didn't turn. A more durable solution was to slightly drill out the escapement arbor to 1.7mm, in the same way I drilled out the other arbors. After this, we were back to reliability. For now :-)</p><p>For illustration, here is the fit as seen in Fusion 360 between the seconds wheel and the escapement wheel:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_wy18yKkn91VPUjpq9UKGM1__y23A-ajvlh_8L9DCU4dk5ueAbv9BFJf2UT0stwXsZLkXUZ5-1a36EsXbePmlNr6I_VUrG2GxhGAjDdy1U_O7z_SCUt3qhaPDw6zSgiSsFZy-KFkh1tU8Nf4mVL_ruDlwrIKn85-XuOrUSMLBce9Q525xuQ/s462/capture_001_21082022_172557.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="389" data-original-width="462" height="269" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_wy18yKkn91VPUjpq9UKGM1__y23A-ajvlh_8L9DCU4dk5ueAbv9BFJf2UT0stwXsZLkXUZ5-1a36EsXbePmlNr6I_VUrG2GxhGAjDdy1U_O7z_SCUt3qhaPDw6zSgiSsFZy-KFkh1tU8Nf4mVL_ruDlwrIKn85-XuOrUSMLBce9Q525xuQ/s320/capture_001_21082022_172557.jpg" width="320" /></a></div><br /><p></p><p>One large square is 5mm. And here is the seconds wheel and the intermediate wheel:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjESb0XF2IDQX3mZq5WGC1JgoVNh8nIw-8ucGqZUSsPRagAZXagUGgQLJGu0S57HoUpAn_jsJOM94jOnN7j5jUDtnzJjbKNpVT3LBE_biwtuxh8irUIQ0x2JqiNwY6L5NycBEaNXwquh5kWgCpCYgLZ4mch0dRr41HQQagLapSPUoOQJM4b1w/s687/capture_002_21082022_172744.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="451" data-original-width="687" height="210" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjESb0XF2IDQX3mZq5WGC1JgoVNh8nIw-8ucGqZUSsPRagAZXagUGgQLJGu0S57HoUpAn_jsJOM94jOnN7j5jUDtnzJjbKNpVT3LBE_biwtuxh8irUIQ0x2JqiNwY6L5NycBEaNXwquh5kWgCpCYgLZ4mch0dRr41HQQagLapSPUoOQJM4b1w/s320/capture_002_21082022_172744.jpg" width="320" /></a></div><br /><p>The clearance is only about 0.3mm in each case.</p><p><br /></p><br /><p><br /></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-72142122353808685182022-08-19T16:37:00.003-07:002022-08-19T16:37:55.151-07:00Clock prototype #4, including a problem solved<p>In prototype 4, I wanted to make more space for the weight drum without changing the overall dimensions of the clock. I worked out one way of doing this was to flip the direction of what I call G2, the gear immediately after the escape wheel, which drives the seconds hand. It changed from this (with the original, incorrect escape wheel):</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFCK5PjUpNS304N7I_vELhSagKTtQFFqgOIeKC_Adv4ZCd_dfzv8encMh2e-Wt4vIivSH6RSC8PATOODpD8azv-qpj-dnXw6UXnGhpGqsxZw1t_YqIR-iU07zi8S4cO2m_rpWImlSTgA_C8iM30O_4hEyB6U6o8-DOUlyPDTuqcPYFhkbK-w/s4080/PXL_20220806_010955513.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFCK5PjUpNS304N7I_vELhSagKTtQFFqgOIeKC_Adv4ZCd_dfzv8encMh2e-Wt4vIivSH6RSC8PATOODpD8azv-qpj-dnXw6UXnGhpGqsxZw1t_YqIR-iU07zi8S4cO2m_rpWImlSTgA_C8iM30O_4hEyB6U6o8-DOUlyPDTuqcPYFhkbK-w/s320/PXL_20220806_010955513.jpg" width="320" /></a></div><p>to this:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg64KrO9GLrgFgyovcCp90t-obQRJgshKTxDO9w3b3Srb_qEBHLBDzDqx2UronZZonSA6ghcYjQwNerZXKhrd7TgReSV97ffO7EyTl-LxnlbdV6YlPlJhICjgeR9s5ZXlJ0k2D4djbThc14VdE8lvKYNfePuxd7WJV2NuDpTS3nmgBNS2DgUA/s4080/PXL_20220816_003300748.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg64KrO9GLrgFgyovcCp90t-obQRJgshKTxDO9w3b3Srb_qEBHLBDzDqx2UronZZonSA6ghcYjQwNerZXKhrd7TgReSV97ffO7EyTl-LxnlbdV6YlPlJhICjgeR9s5ZXlJ0k2D4djbThc14VdE8lvKYNfePuxd7WJV2NuDpTS3nmgBNS2DgUA/s320/PXL_20220816_003300748.jpg" width="320" /></a></div><br /><p>By rotating it through 180 degrees and adjusting the vertical height of some of the other gears, it frees up lots of space on the main arbor. Now the weight drum has enough space for a counterweight, which can be used for winding, and there is also more clearance so that it doesn't rub against the hour wheel. Other rearrangements are possible, and I intend to look at these in a later version. The new weight drum, with sections for the weight cord and the counterweight cord can be seen here:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9bqeNG3laoRxE2bQn1_bB3H0tmCPwV8Dd9TtsA1wQxEUdP7xJPeomTam-DDa4gQw7lS9yxiTcYFAULBbrvMzK_7PfyS97w7mcLI5Wg0EvKyiRvAp8dLu6RKI_nISR_8zLv721ICqM1JwmCamY0uKMA38iet3sph0Dua3mwx3se62Z4V2zZA/s4080/PXL_20220819_230127279.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9bqeNG3laoRxE2bQn1_bB3H0tmCPwV8Dd9TtsA1wQxEUdP7xJPeomTam-DDa4gQw7lS9yxiTcYFAULBbrvMzK_7PfyS97w7mcLI5Wg0EvKyiRvAp8dLu6RKI_nISR_8zLv721ICqM1JwmCamY0uKMA38iet3sph0Dua3mwx3se62Z4V2zZA/s320/PXL_20220819_230127279.jpg" width="241" /></a></div><br /><p>The counterweight cord had just come off in this picture. Apparently I am not very good at tying knots.</p><p>When I first put this together, it did not run well, and I could not get more than a few minutes from it. After a lot of experimentation, it looked like some of the gears didn't have enough clearance and were either seizing or adding friction. Notably, this occurred between the first itermediate gear (G3, between seconds pinion and minutes) and the second intermediate gear (G5, between minutes pinion and hour). I designed the gear without relaxing any tolerances other than allowing some backlash. I had some <a href="https://www.stevesclocks.com/forum/general-discussion/distance-between-gear-centers">discussion with Steve Peterson</a> about this and added gullet to G3 and truncated the teeth of the G4 pinion. Both helped a little but didn't fix the problem, and I was at the point of giving up on the design.</p><p>After a few days of mot thinking about clocks at all, I made up a depthing tool:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPkYMvDRq791llrSCR6g_CXOugb8FTIKAlpr8Jcae2PkVFOslnK7fvUQKAelzCRnbV7pMSJIPprw7GuAAsTLh7Q3z0DwiWidio38p2tUbMjeRaJmpm6yO6qnaoGdz_fcK751ByhZqaGfwbdUKgXcUtH5vk8gtrpfbOrF0MfBCn24Ug0R0s0w/s4080/PXL_20220819_230957525.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPkYMvDRq791llrSCR6g_CXOugb8FTIKAlpr8Jcae2PkVFOslnK7fvUQKAelzCRnbV7pMSJIPprw7GuAAsTLh7Q3z0DwiWidio38p2tUbMjeRaJmpm6yO6qnaoGdz_fcK751ByhZqaGfwbdUKgXcUtH5vk8gtrpfbOrF0MfBCn24Ug0R0s0w/s320/PXL_20220819_230957525.jpg" width="320" /></a></div><p>You can mount the gears on it and adjust their exact distance to see how it affects their running. I don't know that I can trust the exact distances I read from it, but I could see that in some cases, only a few tenths of a millimeter would change the gear pair from spinning loosely, to free but not as loose, to not being very free at all, based on an unscientific method of spinning them and seeing how long they took to stop.</p><p>This suggests that undersizing the gears might be a solution, and it also occurred to me to drill out the arbor holes slightly. After printing, I had drilled the holes in the frame out to 3.1mm diameter, and now I drilled them out to 3.2mm. More exactly, I used a 3.2mm drill. The holes might be a little larger as I drilled them by hand without being very precise about centering the drill. This seemed to make a huge difference, and I was able to get runs of 2 hours or more. I don't think that this makes the arbors run more smoothly in the holes in the frame. It's more likely that it is giving some wiggle room for the gears. There are still some issues, in particular I think G3 has some friction with the hub of G2. Here is a short video:</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/5Oo3d1_p8pw" width="320" youtube-src-id="5Oo3d1_p8pw"></iframe></div><p>The face is loosely attached here. In the end it will have four fixings.</p><p>There are some things I still haven't done: the clutch for the minutes hand, and a smaller diameter weight drum. But after some frustration, I'm happy with this as prototype 4.</p><p><br /></p><p><br /></p><p> </p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-13210384094320618882022-08-07T20:37:00.001-07:002022-08-07T20:37:24.770-07:00Prusa extruder axle problems<p>I've been round the following issue several times now, and so I thought I would document it, even if only for my own future reference. If you find that a Prusa MK3 is manifesting problems like:</p><p>- blobs (like little nodules) on the surface of prints; see the right hand example below.</p><p>- under extrusion and poor layer adhesion, especially when there is a lot of retraction</p><p>- slight extruder clicking</p><p>- in extreme cases, extruder motor overheating</p><p>then the problem may be that the axle for the extruder idler has slipped. This has happened to me several times now. Open up the extruder cover and see if it turns freely. If it feels graunchy, see if you can push the axle in slightly. The movement may then get smoother. If you push it too far, you won't be able to close the door over the idler and can pull it back a bit. This has fixed the problem for me now at least three times, including one case where the axle was slightly bent and needed to be replaced.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFTYnIrXMKQFzLNwC1P75pRbtQ9GRA-6doUJMZzhGkGn-ALaa8UFWYI9MOCHHTat0Q-8H7P4cva4oByHKWY9ayG-AThgc2L19J5Q6cIr6BhHUuVjyrzl-hQLbf5qyhoJNnBjeZoIAITX87gAZZK-xpPE1ULf7jQQABOUr8j79DT1C-gEcPTg/s4032/PXL_20210929_022233235.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3024" data-original-width="4032" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFTYnIrXMKQFzLNwC1P75pRbtQ9GRA-6doUJMZzhGkGn-ALaa8UFWYI9MOCHHTat0Q-8H7P4cva4oByHKWY9ayG-AThgc2L19J5Q6cIr6BhHUuVjyrzl-hQLbf5qyhoJNnBjeZoIAITX87gAZZK-xpPE1ULf7jQQABOUr8j79DT1C-gEcPTg/s320/PXL_20210929_022233235.jpg" width="320" /></a></div><br /><p><br /></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-54731816775481964072022-08-05T19:06:00.001-07:002022-08-05T19:06:19.134-07:00Clock prototype #3<p>The latest prototype gets a bit closer to being a real clock. The frame is much more robust, and has a weight drum connected via a ratchet. Somehow I got a whole lot of things wrong in this version. It simply didn't run for more than a few seconds at first. The pendulum would swing for a short while and then stop. I spent a long time searching for sources of friction, and removing some parts of the mechanism such as the hour train and reprinting or drilling out others. This revealed a few things that could be improved. For example, the bearings for the fork arbor were very tightly fitted, and so unless they were exactly square, this put extra friction on the arbor. However, they real reason turned out to be that I had the fork inverted. The sketch I had constructed from it in Fusion 360 was for an escapement which turned the opposite way. In the earlier prototypes, I had remembered to invert the part but this time I didn't. As a consequence the pallets were oriented wrongly and didn't receive any push from the escape wheel teeth and the pendulum ran out of energy. A definite case of a short circuit between the ears. Once I had fixed this, things worked a lot better - still stalling sometimes, but I have had a test run of 4 hours with no problems.</p><p>Here's a video.</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/72A-HUL11gs" width="320" youtube-src-id="72A-HUL11gs"></iframe></div><p>Now you might think this is recorded at half speed, but it isn't! It seems that I got the gear ratio between the escape wheel and the second wheel wrong. The pendulum is going at the right rate, but everything after that is wrong. The brain really wasn't working well the last few days.</p><p>A couple more pictures:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiIA-0U3uPf7cg8J4s3FW5R_cOnOtY126_Wsp5qbomd7KRxsavOxRjunKFdkSfxD7SbauWrhohqOKTE1UCvT3V4MpnopfmNngmTZXorUWzqn5d37O1ieuvdi6X72pwbhWLrkrFQTbAcIT04vul2BPPQ-mB4nqN9qpZUzwc-VZEdDV418qvVJg/s4080/PXL_20220806_010945341.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiIA-0U3uPf7cg8J4s3FW5R_cOnOtY126_Wsp5qbomd7KRxsavOxRjunKFdkSfxD7SbauWrhohqOKTE1UCvT3V4MpnopfmNngmTZXorUWzqn5d37O1ieuvdi6X72pwbhWLrkrFQTbAcIT04vul2BPPQ-mB4nqN9qpZUzwc-VZEdDV418qvVJg/s320/PXL_20220806_010945341.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgu1opi4Bp3jyX9oLZXNeG-eH1QmAlsF6XremTlsvf2swaEFxa1UIVNFjgW03O_9DSy-1WlFakPpJUqrCegjEe0nfs9TH0vZp9ZYj9KyysVfGg_Appqjf1323onj-QzLN4YXfPlYKNJd56mt4kP_iifK9FtH2DMVoPj3kdA0pHARb1OnaDPQA/s4080/PXL_20220806_010955513.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgu1opi4Bp3jyX9oLZXNeG-eH1QmAlsF6XremTlsvf2swaEFxa1UIVNFjgW03O_9DSy-1WlFakPpJUqrCegjEe0nfs9TH0vZp9ZYj9KyysVfGg_Appqjf1323onj-QzLN4YXfPlYKNJd56mt4kP_iifK9FtH2DMVoPj3kdA0pHARb1OnaDPQA/s320/PXL_20220806_010955513.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiauE1WNIOr48r2zDF3Jqc9i3KltHlmWJkizjQDuoTS0Xzk7v8WNKFV6sF7xcs9eGf1sjIz3u-Bw3C5TlDhVXNMTwY6A_02nr1MfeM_gNd_KSLrm1VVzuyl1OJBzXL63VofDm124lGz1PcOfCPx1nIQ7psWRp-_J8LYRD6lVurOPkcStcE5Fw/s4080/PXL_20220806_011004164.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiauE1WNIOr48r2zDF3Jqc9i3KltHlmWJkizjQDuoTS0Xzk7v8WNKFV6sF7xcs9eGf1sjIz3u-Bw3C5TlDhVXNMTwY6A_02nr1MfeM_gNd_KSLrm1VVzuyl1OJBzXL63VofDm124lGz1PcOfCPx1nIQ7psWRp-_J8LYRD6lVurOPkcStcE5Fw/s320/PXL_20220806_011004164.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-9zWEs9ZecLfbvi52T7LOxAaLUr7cZn2Xk9ovdwa1AKvZnyFDGXSfqtOZR-HWT2QC1M6iTGHMp4RtnEdE8vwWKb02n_vhZnh30UFS_KSeXE4MjJo73Ns5URPjdmIlXCeVQvR1iKwXbtsB0wUCM0si9tmcdCAZtWp6jqzkY205kNJp_AHCWw/s754/capture_001_05082022_181322.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><br /><img border="0" data-original-height="637" data-original-width="754" height="270" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-9zWEs9ZecLfbvi52T7LOxAaLUr7cZn2Xk9ovdwa1AKvZnyFDGXSfqtOZR-HWT2QC1M6iTGHMp4RtnEdE8vwWKb02n_vhZnh30UFS_KSeXE4MjJo73Ns5URPjdmIlXCeVQvR1iKwXbtsB0wUCM0si9tmcdCAZtWp6jqzkY205kNJp_AHCWw/s320/capture_001_05082022_181322.jpg" width="320" /></a></div><div class="separator" style="clear: both; text-align: left;">There are still plenty of things to fix or add:</div><div class="separator" style="clear: both; text-align: left;"><ul style="text-align: left;"><li>the weight drum sometimes slips forward and rubs against the hour wheel. This maybe the cause of the stalling.</li><li>although there is a ratchet on the weight drum, I didn't arrange a mechanism for rewinding the clock, and some changes to the frame would be needed for it.</li><li>I included a clutch on the minute arbor, but didn't get it right. The clutch should allow you to turn the minute hand and have it also turn the hour train. This entails having the minute pinion securely fixed to the arbor and the main minute wheel able to slip. In yet another moment of vagueness, I got this the wrong way round.</li></ul><div>I think a lot of this can be fixed using the same frame (or something very similar), by rearranging the position and orientation of some of the gears. The decision to arrange that all the gears have the same distance between their centers helps here.</div></div><br />Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-55885964164483726542022-07-29T18:33:00.001-07:002022-07-29T18:33:19.030-07:00New clock experiments, part 2<p>For the next round of work on the new clock, I changed the configuration to have a frame which is shorter overall, and with the escapement set off to one side.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-9BwCYEnHoPUwe9Ivz3rqmG6hkg_ndj4tf3BC0ayk3ABoodVK7yiBWvBj_5H9LSw6znGPMqAHGp6RTDnMEo6PS3pstYXag5QZWx3nI2S0hMaXtmFzWUAec2MKgtuybT0A74OJac0fRF3nbxUEt35NOt9FzqF3MM0TDsjfqZMH6Q3O6otAMA/s883/capture_001_27072022_161614.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="743" data-original-width="883" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-9BwCYEnHoPUwe9Ivz3rqmG6hkg_ndj4tf3BC0ayk3ABoodVK7yiBWvBj_5H9LSw6znGPMqAHGp6RTDnMEo6PS3pstYXag5QZWx3nI2S0hMaXtmFzWUAec2MKgtuybT0A74OJac0fRF3nbxUEt35NOt9FzqF3MM0TDsjfqZMH6Q3O6otAMA/w400-h336/capture_001_27072022_161614.jpg" width="400" /></a></div><p>There is nothing holding the end of the side piece in place so it tends to splay out a little, but will do for this phase. (The illustration shows one version of the design. I used different minute wheels and weight drums in the experiments.)</p><p>For the first test, I made a minute wheel with a winding drum built into it, and set the clock going. With a weight of 560g, it ran for a few minutes and then stalled. Raising the weight to 680g, it ran until the weight hit the floor. The weights were not chosen with any care: I use a water bottle, and it's just a result of how much water I put in it.</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/x9SDJ93pVR4" width="320" youtube-src-id="x9SDJ93pVR4"></iframe></div><p>Theory says that for a 50mm drum, you should unwind the string at 15.7 cm per hour if the motion is continuous. This means that for a typical 1.5 m drop, you would get a run time of around 9.6 hours. It's not enough for a practical clock, but will do while I am experimenting. I also added a weight drum on a separate arbor with 3:1 gearing.</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/tRKM1Hz8XHE" width="320" youtube-src-id="tRKM1Hz8XHE"></iframe></div><div class="separator" style="clear: both; text-align: center;"><br /></div><p>(Yes, I know the string is tangled round the gear. It's the only video I took before disassembling it and I noticed it too late. It wasn't tangled when I did the tests.)</p><p>The 3:1 gearing triple the run time to 28.7 hours. However, I didn't get this arrangement to run reliably. It would usually stall after 10-15 minutes, though I did have one run lasting an hour. The weight I was using was 1340g (the heaviest I could get with a water bottle), and this probably explains it. You would expect something more like three times 680g, that is about 2kg, would be needed. I think the frame may also have been starting to distort slightly. Initially when I tried using the 3:1 gearing, I added a 20 tooth gear on the minute arbor, such that both it and the minute wheel were held onto the arbor with set screws. I could not get them to hold tightly enough and one or other would slip. In the end I glued the two gears together, and if I use this in future, I'll print them combined.</p><p>Finally, I put together a rough version a weight drum with a ratchet. I thought this would be straightforward, but ended up going through several variants. Looking at other clocks, I see three main styles:</p><p></p><ul style="text-align: left;"><li>the drum (which in all of these is within the diameter of the minute wheel) has a ratchet on on end, and there are pawls freely pivoted on the minute wheel. Gravity makes them drop into place. A lot of wooden clocks use this.</li><li>the drum has a ratchet on the end and there are sprung pawls attached rigidly to the minute wheel.</li><li>the ratchet is inside the wheel and the pawl are pushed outwards by spring. Used in Steve Peterson's SP5 (on a separate arbot).</li></ul><div>The three styles are illustrated here:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguDnPN726wPDvNC77QJ4TJc1TThtJLP-wDb-QQ1QrghmEGSMkt3FM8nM0T-7JjIyGqEMlGFKBkH0PqTuTbYHVn4-OWHapzrSLUcRfYPdFWDZN09j0VeXdr7Uf2gniLIEv9VtNvm1DqQoAMeJNZJ2DEgUVkgDLhVtPZzeTqoZCW846BjAGZIA/s932/capture_001_28072022_183911.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="548" data-original-width="932" height="235" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEguDnPN726wPDvNC77QJ4TJc1TThtJLP-wDb-QQ1QrghmEGSMkt3FM8nM0T-7JjIyGqEMlGFKBkH0PqTuTbYHVn4-OWHapzrSLUcRfYPdFWDZN09j0VeXdr7Uf2gniLIEv9VtNvm1DqQoAMeJNZJ2DEgUVkgDLhVtPZzeTqoZCW846BjAGZIA/w400-h235/capture_001_28072022_183911.jpg" width="400" /></a></div><br /><div>(Credits: Jacque Favre Clock One, TheGoofy design on Thingiverse, Steve Peterson SP5).</div><div><br /></div><div>I played around with the gravity approach for a bit, but found it hard to get the pawls to drop into place at the right time, and settled on using sprung pawls. They work at any position at any orientation and work well given that you can print thin springy plastic.</div><div><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgtVqmDMF1wj9r8sPglbnzHy5h05IP8mdQIhFUnRFTpVpGWal8mHYZLu_z6q3oJYmwjLDClE8x0AZKw8DwHMhdHUhyiUqFRoWTWYzOeQgqexxxqlEYoG3O2tKMN5iPzE1nZgzOVuzoe2aBLfF2XwxX6U8MkyYt5z_SvNuq7tLkp8ALtPZpxZg/s4080/PXL_20220729_193224809.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgtVqmDMF1wj9r8sPglbnzHy5h05IP8mdQIhFUnRFTpVpGWal8mHYZLu_z6q3oJYmwjLDClE8x0AZKw8DwHMhdHUhyiUqFRoWTWYzOeQgqexxxqlEYoG3O2tKMN5iPzE1nZgzOVuzoe2aBLfF2XwxX6U8MkyYt5z_SvNuq7tLkp8ALtPZpxZg/s320/PXL_20220729_193224809.jpg" width="241" /></a></div><br /><div><br /></div><div>With a 50mm drum, I measured a weight drop of 8cm in 32 minutes, or about 15 cm/hour. There is something puzzling here as some other measurement showed quite different values. I also tried a drum 25mm in diameter. As expected, this halved the drop per hour. You would expect to have to increase the weight, but I got away with the same 680g, albeit with a rather weak tick. It would probably have stalled if I let it go on for longer.</div><div><br /></div><div>I put the weight drum directly on the minute arbor for the tests I've just described. It is not a good way of doing things, as you really need the arbor with the weight to be supported at each end. That doesn't work well with some configurations of the hour train and works even less well if you are going to bring out a seconds arbor. As I mentioned before, a separate weight drum arbor with a 3:1 reduction didn't run without stalling, and so I decided to try 1:1 gearing. There should not be any problems with this, and indeed it worked fine. So this gives me the configuration I want to use for the next version, with the option that the 1:1 gearing could be changed.</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6zAFrP4072ef-J3JBVxeBKw6kyuX-TCup7HMvUYhYBxUtkiL5yZbkRj0-JCRHsuxQuOt_Oh-XXxPiprCZHlCoFDl1oHhrHkI0b3jDK8XPAQLaLC78ema-F8PdIpc2F9F0RCVgow01WnZBT3kFxyomxrxFE-1VaoHbemuTFmK2hChZ-9OdrA/s4080/PXL_20220730_012345523.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6zAFrP4072ef-J3JBVxeBKw6kyuX-TCup7HMvUYhYBxUtkiL5yZbkRj0-JCRHsuxQuOt_Oh-XXxPiprCZHlCoFDl1oHhrHkI0b3jDK8XPAQLaLC78ema-F8PdIpc2F9F0RCVgow01WnZBT3kFxyomxrxFE-1VaoHbemuTFmK2hChZ-9OdrA/s320/PXL_20220730_012345523.jpg" width="241" /></a></div><div><br /></div><p></p><p>Incidentally for some of these prints, I used a 0.6mm nozzle with an Arachne-based slicer (PrusaSlicer 2.5.0 alpha). Allegedly this gives as good precision as a 0.4mm nozzle. See <a href="https://www.youtube.com/watch?v=WgXM2zPusXo">Thomas Sanladerer's video</a> for details. It seems to work well, though I still have a little bit of tuning to reduce stringing and blobbing, and it is more prone to producing elephant's foot. For now, it's good for faster prototyping, and I'll stick with 0.4mm when I want better accuracy.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-26481669357807311202022-07-22T17:32:00.007-07:002022-07-22T18:22:45.078-07:00Designing a new clock<p>It's about a year since I started making 3D printed clocks, with <a href="https://www.stevesclocks.com/sp5">Steve Peterson's SP5 clock</a>, and I decided it was time to try designing a clock of my own. I have modified some of the clocks I've made in small ways (adjusting fit) and in larger ones (replacing the motion work in the Swingtime clock). The only complete design I have done was the William Strutt epicyclic design, and even them much of it came from a published diagram. Now it's time to do something from the ground up. I don't know if I will carry this all the way through to a reliable design; it may turn out I don't have the skills or the patience to do so.</p><p>The starting point is a basic Graham escapement design with a rather conventional wheel train and motion train. I have a few ideas for ways I would like to refine it over time. The gear tooth counts are taken from <a href="https://www.thingiverse.com/thing:4200855">this design on Thingiverse</a>, itself remixed from a design by Thingiverse user TheGoofy. Having said that I wanted to design the clock myself, it might seem inconsistent to take the gearing from an existing design, but there are only so many possibilities which give you the right ratios and a number of teeth that you can manufacture. I like this wheel train as it allows you to add a seconds hand easily. Assuming a pendulum with a 2 second period (so about 1 metre long), you get this:</p><p></p><ul style="text-align: left;"><li>Escape wheel: 30 teeth, pinion 30 teeth.</li><li>Seconds wheel: 60 teeth, pinion 9 teeth.</li><li>Intermediate wheel: 72 teeth, pinion 10 teeth.</li><li>Minute wheel: 75 teeth, 16 teeth.</li><li>Reduction wheel (minutes to hours): 64 teeth, pinion 20 teeth.</li><li>Hour wheel: 60 teeth.</li></ul><div>You have some choice about the gearing from the minute wheel to the weight drum. My initial design has an extra 20 tooth wheel on the minute arbor engaging with a 60 tooth wheel on the weight drum for a 3:1 reduction. If the weight drum has a diameter of 50mm, then it means that for each 3 hour rotation, the weight drops pi times 50mm, so that in 19 hours the weight drops by 1 metre. The pendulum length is something I will reconsider later.</div><div><br /></div><div>I did the design in Fusion 360, using the standard add-in for generating the gears. The add-in only generates involute gears. I feel sure that I read something which said that cycloidal gears are better in the train from the weight to the escapement where each step increases speed and reduces torque, and involutes are better in the train from the minute wheel to the hour wheel, with the opposite characteristics. However, I could not find the reference again and there are many places which say to use involutes unless the teeth are so small they become fragile. <a href="http://gearcutting.blogspot.com/2008/02/comparison-between-involute-and.html">This reference</a> concisely summarizes the debate. If I wanted cycloidal gears there are tools like <a href="http://hessmer.org/gears/CycloidalGearBuilder.html">this one</a> which output a DXF or SVG. I used a 14.5 degree pitch angle and a small amount of backlash to make the spacing between the teeth better. All of the pairs of gears are design to have their centers the same distance apart (60mm) so that I can stack several on the same arbor if I choose, leading to various different modules from 1.33 to 1.5. For the escape wheel and anchor, I used a parametric design a created a few months ago in Fusion 360, based on <a href="https://www.youtube.com/watch?v=A4Vdn0wB2kg&t=250s&ab_channel=JacquesFavre">Jacque Favre's tutorial</a>.</div><div><br /></div><div>(Side note: what I actually did for the gear was use the add-in, and then project the profile into a new sketch. I could then project the pinion profile into a new sketch. This makes combining them a little easier.)</div><p>Here is a picture of a prototype, with a couple of minor parts missing:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgHNHEcGpzQSh3muT6MyiTCWJZG8G5Mp3IMOcAX_yVJTAZEoW4hAzmoLdXutWH1YiXe-8cnDRQz4RADXtEuDWjmPYj320SJxo5WSB1IDJg1tdeC5kHa-vlvp5LY1vJG0S8Rg02fZe5g7PgTMaQyLUIIEoRE2FWffxR2cLdaC-iqhgDNAD0Q_Q/s961/capture_001_22072022_160336.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="719" data-original-width="961" height="299" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgHNHEcGpzQSh3muT6MyiTCWJZG8G5Mp3IMOcAX_yVJTAZEoW4hAzmoLdXutWH1YiXe-8cnDRQz4RADXtEuDWjmPYj320SJxo5WSB1IDJg1tdeC5kHa-vlvp5LY1vJG0S8Rg02fZe5g7PgTMaQyLUIIEoRE2FWffxR2cLdaC-iqhgDNAD0Q_Q/w400-h299/capture_001_22072022_160336.jpg" width="400" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: left;">The purpose of the prototype is to check everything seems to fit together. The weight arrangement is unfinished. It has no ratchet to allow for rewinding. The frame is very flimsy as I designed to print quickly. There are no bearings or attempt to reduce friction in this version, and the anchor is designed so I can experiment with different positions for the pendulum.</div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">I printed part of this: the frame and the wheel train from the escapement through to the minute wheel, modified to include a weight drum. Originally I wanted to try this with various weights to get an idea of what weight I might need in the final version, but I had cut corners in the frame. So in the end it only ran for a few seconds with a weight hooked up. However, by applying force to the minute wheel by hand I was able to see it roughly working:</div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/JyW7Z89ziYI" width="320" youtube-src-id="JyW7Z89ziYI"></iframe></div><div class="separator" style="clear: both; text-align: left;"><br /></div>The beat isn't right and it takes quite a lot of force to make it run, but it gives an idea that things are generally correct.<div><br /></div><div>More, hopefully, to follow.</div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-14824256794184711002022-06-25T14:57:00.001-07:002022-06-25T14:57:36.157-07:00Y Size Limit of the MK3S<p>In an earlier post, I wrote about splitting large gears into parts to print them on a Prusa MK3S. My current project includes a gear which is strictly larger than the official size of the print bed, but by using a trick you can still make it work.</p><p>The gear is 281.33mm in the Y direction from tooth tip to tooth tip. The Prusa MK3S print bed is 250x210mm. However, you can go beyond these limits. First, in the PrusaSlicer printer setting, change the bed size to 250x230mm with an origin offset of 10mm in Y, 10mm being half the difference 230 and 210. Now load the model, move it until it is within the printable area and slice it, with skirt turned off. If you just go ahead and print it, the printer may come up against its Y limits. Nothing terrible happens at this point. You can hear a slight "clunk" as it reaches the limit, and the print it truncated, like this:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQitNAiubB4-Cytv-nbacaNuGa0xirbbtQBlSHGNYq4sVOOiEtAbqkrC0kra0qXP-QJLJ10PHfwk9ji36bG4NgV1tDLuJkGqFZM5iJNL0ZQOnxr0OKwu-vjpz5qmt93ie3n0nLFBtjqX7URSkm_h9kJQcCGYJP4fs20hoiMrj9s7EGf-XveQ/s4080/PXL_20220625_211539244.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhQitNAiubB4-Cytv-nbacaNuGa0xirbbtQBlSHGNYq4sVOOiEtAbqkrC0kra0qXP-QJLJ10PHfwk9ji36bG4NgV1tDLuJkGqFZM5iJNL0ZQOnxr0OKwu-vjpz5qmt93ie3n0nLFBtjqX7URSkm_h9kJQcCGYJP4fs20hoiMrj9s7EGf-XveQ/s320/PXL_20220625_211539244.jpg" width="320" /></a></div><br /><p>The trick is now to adjust the Y position of the model so that we minimize the truncation at both top and bottom. I found that for this model, 103.5mm was the best compromise, leading to a very small amount of truncation:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg__vmvHYLjWXo8-K7iUkWClSfH58qk_RWsn3aW9-W6dRZ0Rrw8m9ksDcrcSC1k9zz34qx8O38rX4IOZ_KbD6bUnStsNoZRxvqSOtfoY2bRFNuLqMJOnW_iqOw4_VTUjlP2Y9jS5YnqlSUaa9K_aUcjp7A-8RkwX1EaTutwaoUVLg8O4lE0pg/s4080/PXL_20220625_215327612.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg__vmvHYLjWXo8-K7iUkWClSfH58qk_RWsn3aW9-W6dRZ0Rrw8m9ksDcrcSC1k9zz34qx8O38rX4IOZ_KbD6bUnStsNoZRxvqSOtfoY2bRFNuLqMJOnW_iqOw4_VTUjlP2Y9jS5YnqlSUaa9K_aUcjp7A-8RkwX1EaTutwaoUVLg8O4lE0pg/s320/PXL_20220625_215327612.jpg" width="320" /></a></div><br /><p>This is probably OK as the very tips of the gear teeth are not doing much.</p><p>Note that you have to peel off the pressure release strip as soon as it has printed, otherwise the print overlaps it.</p><p>This looks to be about the limit of what is achievable. With a slightly smaller model you could avoid any truncation at all while still exceeding the official limits. I guess 217mm would be OK.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-85474799833415396312022-06-05T09:04:00.002-07:002022-06-07T19:35:16.438-07:00Swingtime updateIn my previous post about the Swingtime clock, I noted that the remontoire occasionally goes mad. The motor keeps running until the motor arm collides with the third wheel, long after the tilt switch should have turned it off. I was using a miniature tilt switch of the sort that has two metal balls inside it (<a href="https://learn.adafruit.com/tilt-sensor">like this</a>). I replaced the component I used at first with a second one and got the same result after a day or so of running the clock. The original design called for a mercury tilt switch (<a href="https://en.wikipedia.org/wiki/Mercury_switch">like this</a>) and so I replaced it with <a href="https://www.amazon.com/dp/B073HNMCMN?psc=1&ref=ppx_yo2ov_dt_b_product_details">this one from Amazon</a>. It's a little big for the compartment in the motor arm, but I found that if you open up the plastic package, the actual switch is only about a third of the size. I mounted it and the capacitor on a small piece of veroboard:<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDUkK5E2U0ycH2EpZjpHaax-kAiKYQ4yj7D4dSWU6c8bqxlaPaaBD9ZUbtFmAsJb0k8BtFpIVbhBxwnTrTttpLFGKdMoO7etUx73nVWZRxzDkqMrWjBc7J3IBBqpQjaWzqtzAA416Soc1YCaAYUXMBOmKDzInjbfjnIrHmHmjzHVEvSvGz0w/s4080/PXL_20220605_153643992.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="303" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDUkK5E2U0ycH2EpZjpHaax-kAiKYQ4yj7D4dSWU6c8bqxlaPaaBD9ZUbtFmAsJb0k8BtFpIVbhBxwnTrTttpLFGKdMoO7etUx73nVWZRxzDkqMrWjBc7J3IBBqpQjaWzqtzAA416Soc1YCaAYUXMBOmKDzInjbfjnIrHmHmjzHVEvSvGz0w/w400-h303/PXL_20220605_153643992.jpg" width="400" /></a></div><br /><div>(I know its hard to see. You get the idea and the scale.)</div><div><br /></div><div>It's too early to say whether this works better. However, I've run it for more than a day with no signs of problems. With the original tilt switch, even before the overrun and crash into the third wheel, I would sometimes see it running for longer than expected, and I have not noticed that happening at all with the new switch.</div><div><br /></div><div>One problem remains with the clock: it occasionally squeaks. It is always on certain teeth of the escapement, though it does not squeak every time. Some polishing or lubrication should help. To find when it is happening, I've been taking video at 1/8 speed. Here is an example:</div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/sutpPb1i8HQ" width="320" youtube-src-id="sutpPb1i8HQ"></iframe></div><br /><div><i>Update: after further examination, I think there was more than one source of the squeaking. It got less when I polished the tips of the escapement, and then went away completely after I lubricated the escape wheel arbor. (For now, at least...)</i></div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-34295500660714819312022-05-28T11:03:00.003-07:002022-05-29T10:52:44.586-07:00Swingtime<p>The <a href="https://www.lisaboyer.com/Claytonsite/swingtimepage1.html">Swingtime </a>clock is a design by Clayton Boyer. I previously made his <a href="http://moosteria.blogspot.com/2021/10/the-thriecan-clock.html">Toucan </a>clock. Like the Toucan, the Swingtime is designed to be made out of wood, and I adapted it for 3D printing. I highly recommend watching <a href="https://www.youtube.com/watch?v=vkXskUkNOG8&ab_channel=ShedBuiltStuff">this video</a> to see how it works.</p><p>It's a large clock and this posed some challenges. The main wheel is slightly too large to print on my Prusa MK3S, and so I split it into two pieces, using the technique I described in <a href="http://moosteria.blogspot.com/2022/04/printing-gears-in-parts.html">a previous post</a>. The hourglass-shaped pendulum itself is about 60cm from one end to the other. For this, I printed the center and the two ends, and then joined them together with wooden dowels. One end was still too large to fit the print bed, and so I also split it into two pieces. Finally, the frame is again too large. I found that by reducing it to the minimum size needed, roughly the distance from the escape arbor to the main arbor plus a little extra, it will just about fit diagonally on the print bed. Very long straight objects with a low contact area are one of the hardest things to print without warping. I got lucky and there was only the tiniest lifting from the bed at one end. The whole thing is mounted on a stand of 2020 aluminium. I have lots of this lying around from previous printers, and while it's not as elegant as a wooden stand it does the job. One concern I have is that the very top of the frame is unsupported and the escape arbor sags slightly as a result. I think it's OK, but it will need to be watched over time. I don't recall the amount of weight in pendulum bob, except that it was a lot less than the 140g suggested in the original design. I used some BBs, glued into the bob with wood glue so that they don't shift as the pendulum swings; it doesn't the operation if they do, just makes a slight noise.</p><p>Here's a few pictures and some video.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNocSajZM2p7K-be1IXS61E84WzlzYfzjp9trAnqPLz3puzZSgJz7SUKFtlQS24CxlhvhxcORqJzkA9d8N8OEvyGwL00yjCkiGxFZERUxk40kCNbyvWF8593uluXKOqCVIuZqCxayOoFMtZUoNpdIgwZZticxFe7JudTS-adCchz8eLwJm2A/s4080/PXL_20220528_155803352.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNocSajZM2p7K-be1IXS61E84WzlzYfzjp9trAnqPLz3puzZSgJz7SUKFtlQS24CxlhvhxcORqJzkA9d8N8OEvyGwL00yjCkiGxFZERUxk40kCNbyvWF8593uluXKOqCVIuZqCxayOoFMtZUoNpdIgwZZticxFe7JudTS-adCchz8eLwJm2A/s320/PXL_20220528_155803352.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgN3aG6wUWFDSb3UdzOXq-HVQ7f6NSrBaFGTh6SaR4wX06qKyJxR0MvlLLKxb4m2Ffs5mBrz3G8OilYBQt2h8jCEdAym4i2pz9znaYlF7ywX1S8iwPaT_TLH3rU5b81xM9-aHXL7Rv-byVvh0-3LqU7UkbyqdU5uDCx-N_E_cZ_G_ivZZcYuQ/s4080/PXL_20220528_155816392.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgN3aG6wUWFDSb3UdzOXq-HVQ7f6NSrBaFGTh6SaR4wX06qKyJxR0MvlLLKxb4m2Ffs5mBrz3G8OilYBQt2h8jCEdAym4i2pz9znaYlF7ywX1S8iwPaT_TLH3rU5b81xM9-aHXL7Rv-byVvh0-3LqU7UkbyqdU5uDCx-N_E_cZ_G_ivZZcYuQ/s320/PXL_20220528_155816392.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbMgtfmCCVRA27V0pT7pT4dXZu4wkfWDY0Qq_b8404bASJ3FT89eLqoUb4vYdXoFTeCbHC4CoGokCqhVemQ1zxJ5AImV_ULVe4F7Nr55mKQDyX0yY8FO7uQjk8ofssyc0jubLVsSn0qbv4-jAHIKzaGoEH92bET682O86put7vmJCqU7urTg/s4080/PXL_20220528_155820561.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhbMgtfmCCVRA27V0pT7pT4dXZu4wkfWDY0Qq_b8404bASJ3FT89eLqoUb4vYdXoFTeCbHC4CoGokCqhVemQ1zxJ5AImV_ULVe4F7Nr55mKQDyX0yY8FO7uQjk8ofssyc0jubLVsSn0qbv4-jAHIKzaGoEH92bET682O86put7vmJCqU7urTg/s320/PXL_20220528_155820561.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiD9_aYAGRDzBkhov4ddA3kXez83vzoGgLaJC_wGFBZDLfnKqJfhSvYamHTxDnr5ceiS7mMZ-ZIfBjztgt6NP9JGyrmXcqnTIyDl1ps8u6-m43pLxRVPGOIH7mmpXwNMK0EeIl2O3yNpJOnLlzzYK6s7Tn-s-7uhwmzZ1x3QreVvxk3Wkq35g/s4080/PXL_20220528_155828255.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiD9_aYAGRDzBkhov4ddA3kXez83vzoGgLaJC_wGFBZDLfnKqJfhSvYamHTxDnr5ceiS7mMZ-ZIfBjztgt6NP9JGyrmXcqnTIyDl1ps8u6-m43pLxRVPGOIH7mmpXwNMK0EeIl2O3yNpJOnLlzzYK6s7Tn-s-7uhwmzZ1x3QreVvxk3Wkq35g/s320/PXL_20220528_155828255.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_45rjWo_ZUrJeNYhui3BW1QFJYvsQjPPEfNa2Y-F49zbr4ZDkO2Kh9MJWaB62QkM3DwBs7KIsx0_KyN8D6q0ct2xnEcCzUm9a0klsyl5ivYzj_XviD5B-GZMX66i9EnNIoOrvVE6hNPAVEEOy_zG4b5BfZBdrB63uzHYUzX_NIycoWdzv2A/s4080/PXL_20220528_155837458.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_45rjWo_ZUrJeNYhui3BW1QFJYvsQjPPEfNa2Y-F49zbr4ZDkO2Kh9MJWaB62QkM3DwBs7KIsx0_KyN8D6q0ct2xnEcCzUm9a0klsyl5ivYzj_XviD5B-GZMX66i9EnNIoOrvVE6hNPAVEEOy_zG4b5BfZBdrB63uzHYUzX_NIycoWdzv2A/s320/PXL_20220528_155837458.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhd9lBL3B-fvqvbg8PNbLexkzXsJszsTJm5K1BM2igi9773ViqJOtUjF9P86i3stSKk6mL-HFL39aKAL9XBHRvYpfxD8XLpot2OmOTvE9Gn7Nad83tmVKwdWcFZOC-rAU2Uj1tdDlHakk2UnamsUbe6vvgIijsI4O9yYWPQb0gsIIJVsNM2vQ/s4080/PXL_20220528_155845616.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhd9lBL3B-fvqvbg8PNbLexkzXsJszsTJm5K1BM2igi9773ViqJOtUjF9P86i3stSKk6mL-HFL39aKAL9XBHRvYpfxD8XLpot2OmOTvE9Gn7Nad83tmVKwdWcFZOC-rAU2Uj1tdDlHakk2UnamsUbe6vvgIijsI4O9yYWPQb0gsIIJVsNM2vQ/s320/PXL_20220528_155845616.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/R5ULqv90chc" width="320" youtube-src-id="R5ULqv90chc"></iframe></div><br /><p><br /></p><p>The original design uses a daisy wheel for dividing the minute rotation to the hour rotation. I used this in <a href="http://moosteria.blogspot.com/2021/10/the-daisy-clock.html">a previous clock</a>, and I don't much like the motion it gives. As I noted in the previous post, there are two variants of the daisy wheel design. Clayton Boyer's design uses what I think is the less good one, as it causes the hour hand to move eccentrically. You can see the tip getting closer and further away from the clock face as it rotates. You can see this in <a href="https://www.youtube.com/watch?v=QI_BnnZMGgg&t=3s&ab_channel=BrianGray">another build</a> of the clock, around the 2:50 mark. The daisy mechanism can also give a non-uniform movement in the sense that its angular speed changes as the minute hand advances. One alternative I considered was to use Ferguson's mechanical paradox, as in the <a href="http://moosteria.blogspot.com/2021/11/the-epicyclic-gear-clock-completed.html">William Strutt epicyclic clock</a>. However, after trying several prototypes, I was still unsatisfied with the smoothness of the motion from it. In the end, I used a very conventional 3:1 and 4:1 gear train between the minutes and the hours. It floats freely on the back of the clock face.</p><p>The arbors are 5mm brass, with a 6mm brass tube for mounting the assembly containing the clock face, hands and minute/hour reduction. Each arbor has a small cap. As well as improving the appearance, it stops the gears from gradually sliding forward on the arbors. This was definitely necessary for the third wheel. The pallet rests on has two MR105, chosen because I had some in my parts stores from a previous project.</p><p>The clock is driven by a weight attached to an arm behind the minute gear. The arm contains a motor and a tilt switch. When it drops below a certain angle the motor engages and move the arm up a little. I didn't quite believe that this would work until I saw it happen: why doesn't the force of the motor just drive the minute wheel round rather than raising the motor arm? I think it's that there is enough resistance from the rest of the mechanism, or maybe the escapement is locking everything in place for the short time the motor runs. Or maybe I just don't understand physics. I found that the motor sometimes moved itself up then dropped back down again, similar to what you can see in the first few seconds <a href="https://www.youtube.com/watch?v=QI_BnnZMGgg&t=3s&ab_channel=BrianGray">here</a> (same video as before). The comments thread for that video mentions that Clayton has a modification using a detent to stop this. I had considered something similar. An alternative is to add a capacitor to the motor. This charges up while the tilt switch is engaged and then keeps running the motor after the tilt switch turns off. The motor arm then lifts up a bit further until the capacitor has discharged. It has two beneficial effects: the motor arm raises further so it is longer before the motor has to run again; and as the charge on the capacitor decreases, the motor comes gradually to a halt, which seems to make it hold better. I used 4700uF. The tilt switch is a miniature kind, from <a href="https://www.amazon.com/dp/B00R2MQD1Y?psc=1&ref=ppx_yo2ov_dt_b_product_details">here</a>, and the motor is <a href="https://www.amazon.com/dp/B07JM8V3LH?psc=1&ref=ppx_yo2ov_dt_b_product_details">this one</a>. The distance the motor travels on activation is very variable, anything from moving the motor arm through about 10 degrees to as much as 45 degrees.</p><p>If you look at the end of the video, you can see the remontoire going mad, and driving the motor arm until it collides with the third wheel. At first I though this was because the capacitor was too large, but I now think it was due to the tilt switch getting stuck. The switch contains a small metal ball which joins the contacts, and it's possible that I slightly squished the casing causing the ball to get stuck. It doesn't do this every time, for example the first time I saw it was after a couple of hours, and it clears after a short time. I'm currently trying a replacement tilt switch to see if it helps.</p><p>I like this clock a lot. Clayton's designs are elegant and work well. It looks wonderful and the broad slow swing of the pendulum is lovely to watch and listen to. I'm also emboldened to try some large designs that I would previously have rejected.</p><p><br /></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-57492859925928074112022-04-30T09:58:00.000-07:002022-04-30T09:58:16.855-07:00Printing gears in parts<p>Sometimes I need to print objects which are too large to fit on the print bed by splitting them into parts. I've used this in particular for the frame of some clocks such as the <a href="https://moosteria.blogspot.com/2021/10/the-thriecan-clock.html">Thriecan</a>. I have been reluctant to use this for parts such as gears where the dimensions need to be precise. A project that I am working on calls for a gear too large for me to print, and so I decided to conduct an experiment to see if I can split it and still get a working gear. As with other split parts, I make some 1mm holes in the part and then use metal pins to get the parts into alignment, and glue them with a gel cyanoacrylate. I have been using Loctite UltraGel.</p><p>I made a test piece consisting of a gear about 50mm in diameter, with the split in the gap between teeth. This is the least critical place for functioning of the gear as it never comes into contact with any other gear. I did two versions of the split gear, for reasons which are explained in the "aesthetics" section.</p><p>The results look like this, with the unsplit gear at the top. First, the right way up, and the upside down, with the the side that was in contact with the print bed facing up. I did no finishing on the gears, as you can see from the stringiness. If you enlarge the pictures, the pins are visible. Normally I would trim them to size so that they are hidden.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhDUmd9O8LEEQ6gD9HHyEXgsLXHWMaHa7a-vq2SIC6KHMMDFQlzKNGdHkBCsCp6lcnJyTCm-KpL2a6LxrSXvOBsnjOXf-AjES7PQSsdJz0ASmlc2D8-IDSwTJB7KoQwf2xC4h0RvDoAB-Cbs-6tdLTQGibev3lEqVmMM12LGkaKRPs-QQMgA/s4080/PXL_20220430_160432945.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjhDUmd9O8LEEQ6gD9HHyEXgsLXHWMaHa7a-vq2SIC6KHMMDFQlzKNGdHkBCsCp6lcnJyTCm-KpL2a6LxrSXvOBsnjOXf-AjES7PQSsdJz0ASmlc2D8-IDSwTJB7KoQwf2xC4h0RvDoAB-Cbs-6tdLTQGibev3lEqVmMM12LGkaKRPs-QQMgA/s320/PXL_20220430_160432945.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgaimFzafpt4w3BKJq8ONv-UC0Jmg9k0Vt8WfErlcWmRNyU3nZshBiyU_otiOcSw00VG_TmrkS2KUT2CCuRzhKE_qfcEnPSWF7FYrl_ZOmuqJQZB_qV3skYlsl3E2fcKyTRT7IdtJKU736aJfK2cQVgQFg-pBHCXN7z3DIJ3mQ-4eDfZIc8Kg/s4080/PXL_20220430_160441608.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgaimFzafpt4w3BKJq8ONv-UC0Jmg9k0Vt8WfErlcWmRNyU3nZshBiyU_otiOcSw00VG_TmrkS2KUT2CCuRzhKE_qfcEnPSWF7FYrl_ZOmuqJQZB_qV3skYlsl3E2fcKyTRT7IdtJKU736aJfK2cQVgQFg-pBHCXN7z3DIJ3mQ-4eDfZIc8Kg/s320/PXL_20220430_160441608.jpg" width="241" /></a></div><h4 style="text-align: left;">Dimensional considerations</h4><p>The most important factor is whether the size of the gear is correct, defined as similar for the split and unsplit versions. I measured the distance from the end of a tooth to the one diametrical opposite, across two axes at right angles. I chose the axes like this</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4GOJJf26mPG-hGU9VcqqU035yShHQjUgGNBPo2BpHGA0Hix-8BdNpiAFLntLmYnZWBZqogIk1uJwHkvtuIce0xJ8qmESGGm6O2yfrbudgLtjGwqJXQMo3J_Na8eSOqdFdHxDjEiGeDpdKwFl9wDm1HUBLQlROHTW3emYfyL3XxHlYZ6Sv6A/s702/capture_001_30042022_092034.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="688" data-original-width="702" height="314" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4GOJJf26mPG-hGU9VcqqU035yShHQjUgGNBPo2BpHGA0Hix-8BdNpiAFLntLmYnZWBZqogIk1uJwHkvtuIce0xJ8qmESGGm6O2yfrbudgLtjGwqJXQMo3J_Na8eSOqdFdHxDjEiGeDpdKwFl9wDm1HUBLQlROHTW3emYfyL3XxHlYZ6Sv6A/s320/capture_001_30042022_092034.jpg" width="320" /></a></div><div class="separator" style="clear: both; text-align: left;">so as to emphasize any effects from the split. For the unsplit gear, the axes measured 50.75 and 50.82mm; for the first split gear, 50.71 and 50.83mm; and for the second split gear, 50.58 and 50.89mm. The differences are negligible at this size of gear. They are likely to stay constant in the size of the gear, so by the time we get to something where the gear needs to be split to fit on the print bed (roughly 4 times the size here), they will be even less significant.</div><p></p><h4 style="text-align: left;">Mechanical considerations</h4><div>A second consideration is whether the split will cause weakness in the gear that could affect its operation, either by causing it to deform during use or even to split apart altogether. I don't have any good way of evaluating this. For building clocks, it probably does not matter, as there is not usually a lot of mechanical stress extending across the halves of the gear except near the power source (drive weight, spring, etc.). Even so, the bond is strong. I was not able to pull apart the two halves of the gear except in one spot where I had not applied very much glue.</div><h3 style="text-align: left;">Aesthetic considerations</h3><p>The split can look a bit ugly, or at least noticeable. You can see this quite clearly on the middle gear in the second picture. The third gear shows a possible solution to this, but adding a notch to both the spoke with the split and the other spokes, so they all look similar.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-17983189297717680262022-03-29T14:07:00.001-07:002022-03-29T14:07:26.871-07:00Clutch prints<p>I think this post is mostly directed at my future self, as a reminder of what I did. Here goes anyway.</p><p>I have roller blinds in my house made by Mechoshade. They are the sort where you use a metal beaded cord to raise and lower it. Inside the mechanism there is a clutch, between the indented wheel which the cord engages with, and the hex-shaped shaft of the blind itself. The clutch for one of the blinds has failed multiple times. After the original failure, I printed a replacement in PLA:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjaSp26LeGJ0rjdOAdPDNv2wTv33OIe7UipEm3T7IuUSP7EKPO1gIw8eZoXNdfSGLlCRmq3ZJ-RecLl5xNoAMxWEAvFhYYs7nzHXoftynP__EZZ0118zEYiIm7l7uib9_aSHJ8QdtgQ3QdmianKTQjqMwnl2e2m6CslsJNZOY3gUCO66VBLpA/s3264/IMG_20151024_172654.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3264" data-original-width="2448" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjaSp26LeGJ0rjdOAdPDNv2wTv33OIe7UipEm3T7IuUSP7EKPO1gIw8eZoXNdfSGLlCRmq3ZJ-RecLl5xNoAMxWEAvFhYYs7nzHXoftynP__EZZ0118zEYiIm7l7uib9_aSHJ8QdtgQ3QdmianKTQjqMwnl2e2m6CslsJNZOY3gUCO66VBLpA/s320/IMG_20151024_172654.jpg" width="240" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZWoErE3otzTJPWhqLxVHBAkPArF2bsrt640gf__h6wL4LFxvI6242NdMkHQbPYypj6GZ-KWTeamqok8xczapAhwjfmFy4-7c-WzQFDzGeKGjAhtKNbe3PY-RA3a6WBKmxVIaiLqui-iNmZHL0FLMlwal4LaaCetS2WS-FmmpTYoPBq3GXEg/s3264/IMG_20151025_165216.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3264" data-original-width="2448" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZWoErE3otzTJPWhqLxVHBAkPArF2bsrt640gf__h6wL4LFxvI6242NdMkHQbPYypj6GZ-KWTeamqok8xczapAhwjfmFy4-7c-WzQFDzGeKGjAhtKNbe3PY-RA3a6WBKmxVIaiLqui-iNmZHL0FLMlwal4LaaCetS2WS-FmmpTYoPBq3GXEg/s320/IMG_20151025_165216.jpg" width="240" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjejv4oqBBIahP0fpjxWP5lz77c8HlUVPaf1E0pic75eOK4gvsqFDHgn_hGnfPip_4Aa7WpKU1aaxstUMzvfToF_dUqMqxYATF80gulakJeHb9L3Wq0f46Tyd-e5oFZsETuUspoEuv8pKmslSb6YOMU-p2znZhyg_JLyxGYCNgtqP0LclcEgQ/s3264/IMG_20151025_165230.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="2448" data-original-width="3264" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjejv4oqBBIahP0fpjxWP5lz77c8HlUVPaf1E0pic75eOK4gvsqFDHgn_hGnfPip_4Aa7WpKU1aaxstUMzvfToF_dUqMqxYATF80gulakJeHb9L3Wq0f46Tyd-e5oFZsETuUspoEuv8pKmslSb6YOMU-p2znZhyg_JLyxGYCNgtqP0LclcEgQ/s320/IMG_20151025_165230.jpg" width="320" /></a></div><p>This was in October 2015. I have not tracked how often it has failed since. It's probably two or three times. Usually I print the replacements at 0.2mm layers, 100% infill (if I remember), using PLA. I have tried PETG, which failed immediately. The most recent replacement was a few days ago, and I hope it will hold for a year or two. However, this got me thinking about other materials. Ideally you want something which is strong but not brittle. Strong, because the blind is heavy and I am not always gentle with the cord. Brittle materials tend to fail suddenly after multiple stress cycles, which seems likely to be the case here. PLA has the strength, but is also brittle. PETG didn't work because it is not very strong. <a href="https://taulman3d.com/how-to-choose.html">A chart on Taulman's web pages</a> gives a good guide to the material characteristics. I decided to look at nylon and two related filaments.</p><p>For Nylon itself, I bought a 200g roll from Gizmodorks. I didn't note the exact print settings I used. The results were not great. A first attempt had a poor finish with blobs all over the surface. I think this was at 250. A second attempt with a lower temperature had a better finish but the print delaminated. It is possible that the filament had not been kept well. Nylon is hygroscopic and some sites say that even a few hours exposure to the air will make it damp enough to cause problems. The print surface was blue tape with glue stick. Blue tape on its own was not enough, and when using an unknown filament I prefer not to use PEI sheets so as not to risk damaging them.</p><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUBs2nTjYDPfFKwD4JvvLXMZLsU2RLFtm1JvRZaiHn1sh6Ge8N7wg7AkPGZDnJ2ZdP_O6PHNNRFaV8Ni22n15gAlFAg5huxNDPF3kwH638aOY-c_HfjdsLtYiVCUKZZP7wViysOWFZquqgXs74K2e6glMmaZLRFEvDFW2fnZ3EKo_hyUPuxg/s4080/PXL_20220318_034532910.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUBs2nTjYDPfFKwD4JvvLXMZLsU2RLFtm1JvRZaiHn1sh6Ge8N7wg7AkPGZDnJ2ZdP_O6PHNNRFaV8Ni22n15gAlFAg5huxNDPF3kwH638aOY-c_HfjdsLtYiVCUKZZP7wViysOWFZquqgXs74K2e6glMmaZLRFEvDFW2fnZ3EKo_hyUPuxg/s320/PXL_20220318_034532910.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEinSZ4fQ9tIva5bE1xHsbgzkFkO4OZ4GfFnljMe9TYhNGc8JCISWDz8P-2ObnB6UwNGl848Z8GGm1KcjmeNa6G7y07qLyIsH-Zl25xtY2QowSrk66UxM-ZD1EBAJ5Q3cSFCmb52eTS9OHaYdhbn5kA1TL2emh7O-h3I7doEcgLP7rnzrtIO5Q/s4080/PXL_20220318_180558635.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEinSZ4fQ9tIva5bE1xHsbgzkFkO4OZ4GfFnljMe9TYhNGc8JCISWDz8P-2ObnB6UwNGl848Z8GGm1KcjmeNa6G7y07qLyIsH-Zl25xtY2QowSrk66UxM-ZD1EBAJ5Q3cSFCmb52eTS9OHaYdhbn5kA1TL2emh7O-h3I7doEcgLP7rnzrtIO5Q/s320/PXL_20220318_180558635.jpg" width="241" /></a></div><br /><p>Next, I tried Taulman PCTPE. As I understand it, this is a mixture of nylon and a flexible filament similar to TPU. I used it once before, a long time ago, to make a headphone holder and found it to be very strong. For the print settings, I started with one of the flexible filament profiles in PrusaSlicer, and increased the volumetric flow rate to 5mm^3/s. Initial attempts on blue tape warped. Blue tape with glue stick worked. I also started with 240/50 and then reduced it to 220/50 for the successful print. You can hear bubbles popping a higher temperature and see water vapor coming off it. The result is quite flexible, possibly too much for the clutch.</p><p>Finally, I tried Taulman 910. This is supposed to be very strong under tension, while still having some flexibility. Some people say it is hard to print with and needs a high temperature and an enclosure. For met it worked fine at 240/50 on blue tape with no need for glue stick. The result is a little more flexible than I expected. It definitely feels strong; I have no way of evaluating this more precisely.</p><p>Warped PCTPE:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmUKka4WyiD2rp5MZFl1sTYmcbNqnpJp_Q0SzuBCmO7qRDu-X5vYnwAuxd-oGYiNpOeW2sT5CE3vwEc55ZOrCadwa7eKyhTbKptBSG8egjtTYY-t-lG2brPiBnyEOa3WJR6Si0aFSud9jYJRZClfHerknv_lm5tR_rUt46WinMUyJEmrXH6A/s4080/PXL_20220329_205529786.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmUKka4WyiD2rp5MZFl1sTYmcbNqnpJp_Q0SzuBCmO7qRDu-X5vYnwAuxd-oGYiNpOeW2sT5CE3vwEc55ZOrCadwa7eKyhTbKptBSG8egjtTYY-t-lG2brPiBnyEOa3WJR6Si0aFSud9jYJRZClfHerknv_lm5tR_rUt46WinMUyJEmrXH6A/s320/PXL_20220329_205529786.jpg" width="320" /></a></div><br /><p>PCTPE and 910:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj0Q_L8ayj1Ex-0kvcCBIKeceYq3eyE8z5QUleZgKJHBAbtfGeGNLN1rmgTpE8v0exN6_Dveg9eEgCSrjuKoE-Qb0u_y6SeQHCrSBDWHwX7B17w0NcmPtKRTwImd0gXluO437m5ME3jxAAJUsM3OsjttA4zA4j_FpcXAiawhxuE4zXLoKGhZA/s4080/PXL_20220329_205533504.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3072" data-original-width="4080" height="241" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj0Q_L8ayj1Ex-0kvcCBIKeceYq3eyE8z5QUleZgKJHBAbtfGeGNLN1rmgTpE8v0exN6_Dveg9eEgCSrjuKoE-Qb0u_y6SeQHCrSBDWHwX7B17w0NcmPtKRTwImd0gXluO437m5ME3jxAAJUsM3OsjttA4zA4j_FpcXAiawhxuE4zXLoKGhZA/s320/PXL_20220329_205533504.jpg" width="320" /></a></div><br /><p>(Sorry for the poor pics. My camera was having difficulty focussing.)</p><p>I have not fitted the new clutches yet. It's a nuisance to take the blind apart so I'll wait until it fails again. This might not be for a year or two.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-85716116308272349202022-03-22T20:18:00.000-07:002022-03-22T20:18:47.090-07:00Favre's Clock 24<p>Jacques Favre has designed several interesting clocks, the designs for which are <a href="https://www.myminifactory.com/users/jacprint">available on myminifactory</a>. I built his <a href="https://www.myminifactory.com/object/3d-print-clock-24-174025">Clock 24</a> design. It is weight driven, and uses a Graham escapement. The run time when it is mounted at a reasonable height (5 feet or so) is about 24 hours. This could be increased by using doubling the weight cord through a pulley.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQJs5cuGfWcHZt7eIqsTgQ4ubxb84hL-3uoaIRSA-8uyVG11rh-rkWit2-xeuJFHaOYlnMWYVr2HF0-CHwc3i-eQvcG82s9ee-N8wasGSUX2k90qVoiCDfjbRYJAJ9ALlWl16bPJYrvYMq-FPuHXlyRarAO6bu6PWVOzDOIyzWDBD0dwROgg/s4080/PXL_20220322_231700265.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQJs5cuGfWcHZt7eIqsTgQ4ubxb84hL-3uoaIRSA-8uyVG11rh-rkWit2-xeuJFHaOYlnMWYVr2HF0-CHwc3i-eQvcG82s9ee-N8wasGSUX2k90qVoiCDfjbRYJAJ9ALlWl16bPJYrvYMq-FPuHXlyRarAO6bu6PWVOzDOIyzWDBD0dwROgg/s320/PXL_20220322_231700265.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5LonkqivPA2r70wn2MDZkT0CLh9sz_lb1ekvsxSe8oMgkyJl8Fe-VFOGQJJ1MZ04zeNKGsmw55pFz7M0mbIb6Bc5URW_wa-_3ziJdpzG342e9tS4jiOaP06OgnoXJKP9XYqe6U_3ksir7iARNSseP2EuXUylX3IEca1KLoK3214gPRmFC-g/s4080/PXL_20220322_231711341.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg5LonkqivPA2r70wn2MDZkT0CLh9sz_lb1ekvsxSe8oMgkyJl8Fe-VFOGQJJ1MZ04zeNKGsmw55pFz7M0mbIb6Bc5URW_wa-_3ziJdpzG342e9tS4jiOaP06OgnoXJKP9XYqe6U_3ksir7iARNSseP2EuXUylX3IEca1KLoK3214gPRmFC-g/s320/PXL_20220322_231711341.jpg" width="241" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/nms6l-xwfE0" width="320" youtube-src-id="nms6l-xwfE0"></iframe></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/i9CYbS6AQoE" width="320" youtube-src-id="i9CYbS6AQoE"></iframe></div><p>One striking thing about Clock 24 compared to all of the others that I've made is that it is huge. The scape wheel and largest gears are almost twice the diameter of the ones in the <a href="http://moosteria.blogspot.com/2021/08/steve-petersons-3d-printed-clock.html">first Peterson clock</a> and the frame is corresponding larger. It uses arbors of 5mm and 2mm diameter, compared to 3mm and 1.5mm in the Peterson clock. I'm not sure of the consequences of this for ease of getting it going. I think it probably makes it a little less sensitive to printing tolerances. Does it make it more or less sensitive to friction? The contact area with the arbors is larger (more friction) but bears less force per unit area (less friction). I just don't know. As with previous clocks, I used brass rods for the arbors as it's easy to cut them without power tools.</p><p>I found it quite easy to get going after a made a few small adjustments; mostly adding some extra washers to keep some of the gears clear of each other. There are a few variants for the design, the most interesting being in the mechanism which goes between then main gear train (known as the going train) and the winding gear (which carries the weight). This can either be two gears with a simple ratchet, or a more complex design with a spring to act as a power reserve for the going train during winding. I elected to go with the simpler option. The escape wheel also has two variants, one with full depth teeth and one with tapered teeth which may have lower friction. I started with the tapered version, but found that the anchor tended to wobble as it only has a small area of contact with the escape wheel teeth. The non-tapered version worked better.</p><p>One interesting design choice is the clutch. In the Peterson clock, this is done by a spring which holds a gear and a spacer in contact. The <a href="http://moosteria.blogspot.com/2021/10/the-thriecan-clock.html">Clayton Boyer design</a> that I built uses a small pad of leather held against the arbor with set screw. Favre's clutch sandwiches the arbor between two metal rods with screws to adjust how tightly it is held. I didn't take a picture before assembling the clock but perhaps you can see it here:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6hIuyyZ7JgHQSec3N5AgkRL24-vLfjiRnw_8tinhuxq1Oykxk4hBYeAtFivrteawKbfyLRC79Z6p5w6RUthc4t3BW5AIRKkwpKYqOnN8o8mVLxJ2Ho-lmLjR81_izDttIuT6xkrWAtEB0xYAvTyVqBCW8w1xmKpUb8NwlnqCMw5XCWo-LYA/s4080/PXL_20220323_025448743.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4080" data-original-width="3072" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj6hIuyyZ7JgHQSec3N5AgkRL24-vLfjiRnw_8tinhuxq1Oykxk4hBYeAtFivrteawKbfyLRC79Z6p5w6RUthc4t3BW5AIRKkwpKYqOnN8o8mVLxJ2Ho-lmLjR81_izDttIuT6xkrWAtEB0xYAvTyVqBCW8w1xmKpUb8NwlnqCMw5XCWo-LYA/s320/PXL_20220323_025448743.jpg" width="241" /></a></div><p>Or perhaps not.</p><p>I am still testing the clock. I have the timing quite well tuned now. The weight is about 1.3kg; less might work. As I write this, it has been running for a bit over 12 hours continuously. A couple of previous runs stopped after 1-2 hours and it seems that something was binding. Some of the previous clocks have stopped when friction has consumed too much of the power of the clock. You see the pendulum losing more and more of it swing and finally dropping below the amount needed to engage with the escape wheel. When Clock 24 stopped, it seemed more like something in the gear train had locked up, and it took a nudge to free it and get things going. It may be that the gear can't move freely enough on the arbors (not enough <a href="https://nobswatchmaker.com/blog/simplifying-the-art-of-endshake-in-watchmaking#:~:text=Endshake%20is%20the%20amount%20of,that%20holds%20the%20part%20in.">endshake</a> maybe). If it binds again, I'll see if I can get a better idea of what is going on.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com1tag:blogger.com,1999:blog-8371051.post-68480999956441063082022-03-03T21:34:00.002-08:002022-03-03T21:34:23.470-08:00Two minor clock projects and an update<p>I recently completed a couple of new clocks, both brief experiments.</p><p><b>Neopixel clock</b></p><p>The first uses a circular array of WS2812 LEDs, sometimes known as neopixels. It's hard to take good pictures of it, as the brightness of the LEDs overwhelms the camera on my phone. This will give a general idea:</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/IauKhWuzDAg" width="320" youtube-src-id="IauKhWuzDAg"></iframe></div><p><br /></p><p>The LEDs are <a href="https://www.amazon.com/dp/B083VWVP3J?psc=1&ref=ppx_yo2_dt_b_product_details">this product</a>. It consists of several concentric rings which different numbers of pixels. It's a nice, cheap product and comes with connectors so that you can use just some of the rings and address them in any order. The only alternative I found was an <a href="https://www.adafruit.com/product/1768">overpriced product from Adafuit</a>.</p><p>The outermost ring has 60, making it suitable for minutes and seconds, and the next has 48, meaning you can displays hours down to quarter-hour resolution. I use the next ring, with 40 pixels for a temperature display, although that part of the software is not complete. The controller is a <a href="https://shop.m5stack.com/products/m5stickc-plus-esp32-pico-mini-iot-development-kit">M5StickC Plus</a>. Strictly speaking a level shifter should be used between the 3.3V output of the ESP32 in the M5, and the 5V needed for the control pin of the pixels, but it seemed to work OK without one. The only problem I had was during prototyping when I had it connected up through leads with alligator clips. For some reason, the signals got corrupted in this case. Using a breadboard or soldered connections works fine. The hours and minutes are displayed as a sort of swoosh with several LEDs at different brightnesses. The case is 3D printed in clear PLA. This does make the pixels a bit fuzzy, though most of the fuzziness in the video is from the camera.</p><p>The neopixel clock is not very practical. It's surprisingly hard to read the time without hands to direct your eye. I hoped the swooshes would help, but they really don't: every time I look at it, it takes a few seconds to read off the time, when it ought to be near-instantaneous.</p><p><b>Favre's Full Clock</b></p><p>The second recent build is <a href="https://www.myminifactory.com/object/3d-print-the-full-clock-95407">Jacques Favre's "full clock"</a>. It's a straightforward clock mechanism driven by a small stepper motor, the widely used 28BYJ48. I used the ULN8003 driver board that came with the one I bought instead of the L293D preferred by Favre. The clock needs two 608 bearings, and there are printable versions. I had several 608s in stock, so used them instead.</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/WBAcEwJcVEs" width="320" youtube-src-id="WBAcEwJcVEs"></iframe></div><p><br /></p><p>The clock runs silently and smoothly. I like this design better than Steve Peterson's stepper clock (see <a href="http://moosteria.blogspot.com/2021/09/steve-petersons-stepper-clock.html">this post</a>), which is not quite as quiet and slightly jouncy in its movement. One concern is whether the 28BYJ48 will stand up to continuous running as they aren't really designed for it.</p><p>I am thinking of making some of Favre's other clocks, and this short project was meant as a way of learning more about his design style. Almost all of the parts worked fine. The only modifications I made were to shrink two parts with an inner thread by 95% for a better fit, and to make the hands a bit less boxy. There are some shafts glued together from two halves and I made 1mm diameter holes in them so I could use a pin or piece of wire to keep them aligned while the glue set.</p><p><b>Peterson 10 day clock update</b></p><p><a href="http://moosteria.blogspot.com/2021/08/steve-petersons-3d-printed-clock.html">Steve Peterson's 10 day clock</a> was the first one I made. One problem I have had with it is that after a few weeks of running, the pendulum amplitude gets less and less until it stalls. Reading the comments thread on his myminifactory page, this is a problem which several people have had. The proposed solution is always to find ways of reducing friction, and I have been through several cycles of doing so: re-cleaning the bearings, polishing the arbors, reprinting the gears in regular PLA instead of silk PLA, lubricating with white lithium grease. I also tried adding more weight. The pattern has been the same every time: it seems good at first, but after 4-6 weeks of use, the problem recurs. I'm now trying ceramic bearings to again try to bring down the friction. We'll see what happens.</p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-72045835751310349712021-11-27T19:14:00.002-08:002021-11-27T19:14:56.894-08:00The Epicyclic Gear Clock Completed<p>Last time, I wrote about the design considerations for a clock adapted from William Strutt's epicyclic gear clock. Now it is time to complete the design by adding the frame and the driving/timing mechanism. There is one small change I made to the design documented in the previous post. The planet gear is mounted on a carrier pivoted on the minute arbor. This works better if you add a counterweight opposite the planet gear. A US quarter seems to be about right.</p><p>A few pictures and video of the completed design first, and then I'll fill in a few details.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiC3B4Wvk5u5yqAFbbeVwYgQYeBO3kRTnRplZxSsvuaUon2Ot70IS60JcckvZTs6dq8N1JE45UcHafH7CVTgIzX5ntKBIb84uwvCmwKbto2l0dQyTsUFD0DwDK5Xd3DzkWGPrdb/s4032/PXL_20211128_030220054.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiC3B4Wvk5u5yqAFbbeVwYgQYeBO3kRTnRplZxSsvuaUon2Ot70IS60JcckvZTs6dq8N1JE45UcHafH7CVTgIzX5ntKBIb84uwvCmwKbto2l0dQyTsUFD0DwDK5Xd3DzkWGPrdb/s320/PXL_20211128_030220054.jpg" width="240" /></a></div><p><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIYLHMHx_WMPKc_st8-i5wQrqXs8afsh95dCnlYvtdN8KrXZUOprLtu0csp2cDGUUSAP50BPFBn3-HI4BO1jhRbEr6Ws0RESOvsjWhKVY1j-Rw8-VbNFAwVD7p7q1iY-PHjCO2/s4032/PXL_20211128_025428899.MP.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjIYLHMHx_WMPKc_st8-i5wQrqXs8afsh95dCnlYvtdN8KrXZUOprLtu0csp2cDGUUSAP50BPFBn3-HI4BO1jhRbEr6Ws0RESOvsjWhKVY1j-Rw8-VbNFAwVD7p7q1iY-PHjCO2/s320/PXL_20211128_025428899.MP.jpg" width="240" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPri-WJUuFT1l1KGAzXdo0hbFZXGnv9vfuvapB7LZi7UoJowUw_bK3_R4mTAcfzaVrTHkHOOBb4ChUPVEfNsdXVGSYGKFGE5_VhWzx6cGi75hP4nkdxbNcCE315aQeWvNJ1qfs/s4032/PXL_20211128_025451911.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3024" data-original-width="4032" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgPri-WJUuFT1l1KGAzXdo0hbFZXGnv9vfuvapB7LZi7UoJowUw_bK3_R4mTAcfzaVrTHkHOOBb4ChUPVEfNsdXVGSYGKFGE5_VhWzx6cGi75hP4nkdxbNcCE315aQeWvNJ1qfs/s320/PXL_20211128_025451911.jpg" width="320" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgYaLKo3dszijjRVvIXIElLi-R-OjD6n0cfuHX-YcSVyLVkNu6CnSrzh0kGcufkgQUD8_3Mi4mgjiJT8bAJgdEYQjLDxOTBIQTkfSxfCL1J37226SNSUhmuEdbk6ReF8tXmpgCw/s4032/PXL_20211128_025509522.MP.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3024" data-original-width="4032" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgYaLKo3dszijjRVvIXIElLi-R-OjD6n0cfuHX-YcSVyLVkNu6CnSrzh0kGcufkgQUD8_3Mi4mgjiJT8bAJgdEYQjLDxOTBIQTkfSxfCL1J37226SNSUhmuEdbk6ReF8tXmpgCw/s320/PXL_20211128_025509522.MP.jpg" width="320" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/dR3y-6C9Yx8" width="320" youtube-src-id="dR3y-6C9Yx8"></iframe></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/oD4GVzK8rl4" width="320" youtube-src-id="oD4GVzK8rl4"></iframe></div><p><b>The Frame</b></p><p>The frame for Strutt's original design (illustrated <a href="http://www.awci.com/wp-content/uploads/ht/2005/2005-01-web.pdf">here</a>) is rather ornate and a little too fancy for my tastes. I like the frame seen on a <a href="https://grabcad.com/library/william-strutt-epicyclical-geared-clock-my-wall-mounted-version-in-laser-cutting-plywood-design-1">GrabCAD version</a> and used this as the starting point for my own. The overall frame has to be taller than will fit on the print bed. In previous designs, I've looked for a point where I can split the frame and then joined the pieces with glue and pins. For my design, I decided to print it so that the very top part attaches with a couple of screws. This also allowed me to defer the decision about the drive and timing mechanism. Depending on what I decided, I could print the top pieces with different dimensions.</p><p><b>Drive and Timing</b></p><p>Most of the remaining design decisions concerned the drive and timing mechanism, that is how to get power into the clock and how to make it run at the right rate. The original clock used a spring, but I was not sure the plastic design would hold up to the stresses from it. Another option was to drive it with a weight attached to the minute arbor. The works OK for a wall mounted clock, but is not suitable for a desk clock. I toyed with using a stepper motor, but again did not like this. In the end I settled on the same drive as my two previous clocks: an electromagnetic pendulum. As before, the pendulum rotates a cam, causing pawls to engage with a toothed wheel. I'll call it an escape wheel, though this might not be an accurate use of terminology. The escape wheel then drives the ring gear via a pinion.</p><p>There are several design considerations. The number of teeth on the pinion and escape wheel must be chosen to drive the ring gear at the right rate; details of the calculations are in the previous post. The period of the escape wheel then determines the length of the pendulum, which must be less than the height of the frame at the pivot point of the cam. Finally, the teeth on the escape wheel must be large enough for the pawl to engage with it reliably. I considered reusing the exact escape wheel dimensions from one of the previous designs, but the escape wheel looks large and out of proportion. A smaller escape wheel is possible, but it must then have fewer teeth so that they are a reasonable size. After some playing around I decided on an escape wheel about 80mm in diameter with 40 teeth, with an 8 tooth pinion. This is about the smallest size of pinion that I was willing to trust. I used a trick I learned from Steve Peterson for the pinion. As only one face comes into contact with the ring gear, you can fatten up the teeth and make them stronger by displacing the trailing face.</p><p>With the gears I chose before, the ring must rotate once every 754.49 seconds, and the escape wheel then rotates each 8/168*754.49 = 35.928 seconds. Each complete swing on the pendulum advances it by one tooth, so the time per swing of the pendulum is 35.928/40 = 0.8982 seconds. An ideal pendulum for this period would then be almost exactly 200mm long, which fits well with the size of the frame.</p><p><i>Cam and pawl dimensions</i></p><p>I'll come back to the pendulum design in a moment, but first there is the question of how to design the cam and pawls given the escape wheel. A reason for wanting to reuse the previous designs is that I knew they worked. Unlike designs for standard escapements (such as the Graham escapement), I couldn't find any guidelines for working out the geometry. To solve this, I set up a sketch in Fusion 360 to try to make sure it would all work. Here is an annotated version:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjr00QPp1IKdnczIoFMJAoTJWGXgQNJ-gclVdI010Do3oSpKb55oM8tFloQYWw5ZA35Z1p8434TePTcFAhjouVHytuW1NSYZR_BocCClbfQKgnNv4D8iaKBjJ8SdEfNKrG6iXgM/s960/Untitled+drawing.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="720" data-original-width="960" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjr00QPp1IKdnczIoFMJAoTJWGXgQNJ-gclVdI010Do3oSpKb55oM8tFloQYWw5ZA35Z1p8434TePTcFAhjouVHytuW1NSYZR_BocCClbfQKgnNv4D8iaKBjJ8SdEfNKrG6iXgM/s320/Untitled+drawing.jpg" width="320" /></a></div><div class="separator" style="clear: both; text-align: left;">Circle A represents the circle at the base of the teeth, B is the pivot point of the cam, and C and D are the pivot points of the driving pawl at the limits of the pendulum's motion. p and q are the points where the end of the pawl would contact the teeth. The angles of lines BC and BD are set by how far the pendulum swings. Experiments with the previous clocks suggest it is about 20 degrees. We can freely choose most of the other dimensions: the escape wheel diameter, the position of the cam pivot, the length of the cam, and the length of the pawl (Cp and Dq). I could then measure the angle between the pawl position at the extreme ends of the pendulum swing: the angle between the radii to p and q. This must be more than the angle between two teeth, 9 degrees for a 40 tooth wheel, but less than the angle between two teeth, as we don't want to advance the wheel too far. Based on this, I was able to choose dimensions which appeared to work, and validated them with a quick and incomplete print.</div><div><br /></div><i>The pendulum</i><div><br /></div><div>I mentioned that an ideal pendulum would be 200mm long. The actual pendulum for this clock deviates from ideal in multiple ways. The period calculation for a pendulum assumes the angle through which is swings is small (a few degrees), while the electromagnetic pendulum in this clock swings by something like 30 degrees. Secondly, in the ideal case, there is a mass just at the end of the pendulum. We have to have the magnet at the end, and the position of this is fixed so that it is close to the drive coil. To make it possible to adjust the timing, there is also a moveable weight bob. In the last two design, I made the pendulum shaft from a brass rod. The weight bob was held in place with a set screw, making fine adjustment tricky. This time round, I printed the pendulum shaft with a thread cut in it, and made both the weight bob and magnet holder similarly threaded. Adjustment is then much easier, and a lock nut can be used to hold the weight bob in position once the timing has been set. The weight bob is just a small printed part with a couple of M5 bolts attached to it. There are two 12mm x 3mm neodymium magnets.</div><div><br /></div><div>The electronic circuit is the one I described <a href="http://moosteria.blogspot.com/2021/10/driver-for-electromagnetic-pendulum.html">a while back</a>. It is controlled by an Arduino Nano, and this has the nice property that the code can measure the pendulum period and report it over the Nanon's serial connection. The electronics enclosure is a bodge, with various things held in place with blue tape and an opening for the USB port which is far too large. It's held to the frame with a rather flimsy bracket. One day I will come back and do this properly. Maybe.</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKrKl4aQhy9ww30ia5hhj4kZ-vVYUAe0FU-1NT_sXXYKTWJVtTppn8b7lI0tR1kdECotnPlKj2umGhNYExa0nGxKaFFlZ4pk98aD7G5XMFTQGJ3t2lZ58bq0BqJ_GDbvK1-v4T/s4032/PXL_20211128_010945976.MP.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKrKl4aQhy9ww30ia5hhj4kZ-vVYUAe0FU-1NT_sXXYKTWJVtTppn8b7lI0tR1kdECotnPlKj2umGhNYExa0nGxKaFFlZ4pk98aD7G5XMFTQGJ3t2lZ58bq0BqJ_GDbvK1-v4T/s320/PXL_20211128_010945976.MP.jpg" width="240" /></a></div><br /><div>The pendulum moved very vigorously - so much so that the frame rocks slightly. If I did a redesign, I would make it a bit heavier. The clock is very quiet compared to the two other electromagnetic clocks.</div><div><br /></div><div><b>Wrap up</b></div><div><b><br /></b></div><div>This is my eighth clock and the first one I have designed entirely, other than drawing the initial inspiration and (initially) the gear ratios from Strutt's original. I went though multiple iterations both in silico with Fusion 360 and in the printed parts. It's a cliche to post a picture of your box of rejected parts, so I won't. I'm happy with the end result.<br /><p><br /></p></div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com6tag:blogger.com,1999:blog-8371051.post-17080084952072349182021-11-01T18:35:00.004-07:002021-11-20T19:01:16.236-08:00William Strutt's epicyclic gear clock: design and prototype<p>In the early 1800s, William Strutt designed a clock based on an epicyclic gear train. There is a good description of it in <a href="http://www.awci.com/wp-content/uploads/ht/2005/2005-01-web.pdf">an edition of the Horological Times</a>. The key elements of the gear train are shown in the following illustration. The frame, escape wheel and driving force are omitted.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSAG5vD9meQY9hNloQ3H2V12KEfQA7E8Ht93mWXhM3DS9KTAevkjlmzGXVdUT90mLon14rgFN0NbLTohL3c5FZ-kwxdWj6NTrRfAiIjir6c7HBZkh1JZHosP01siaaoYF6QQnK/s1024/0812cae7-9793-4372-bb2c-10fa9a446e79.JPEG" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="768" data-original-width="1024" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjSAG5vD9meQY9hNloQ3H2V12KEfQA7E8Ht93mWXhM3DS9KTAevkjlmzGXVdUT90mLon14rgFN0NbLTohL3c5FZ-kwxdWj6NTrRfAiIjir6c7HBZkh1JZHosP01siaaoYF6QQnK/w400-h300/0812cae7-9793-4372-bb2c-10fa9a446e79.JPEG" width="400" /></a></div><br /><p>To understand how this works, start from the minute arbor. It is attached rigidly to the planet carrier (white). As the carrier revolves, it moves the planet gear (green). The blue gear is one of two sun gears and is fixed to the frame (not shown). The movement of the planet gear has two effects. Firstly, it turns the ring gear (red). At the top, you can just see a small pinion (also green), which would be attached to the escape wheel. This therefore regulates the time. The period of the escapement and the gear ratios are chosen so that the planet carrier rotates once per hour, as required for the minute arbor. The final element is the hour gear (yellow). It is also a sun gear, and is free to rotate on the minute arbor. It has the same diameter but a different number of teeth is different to the fixed sun gear. This is an implementation of <a href="http://www.horo-logical.co.uk/ferguson.html">Ferguson's mechanical paradox</a>. The rotation of the planet gear causes the free sun to rotate at 1/12th of the rate of planet around the fixed sun, providing the rotation for the hour hand.</p><p>There are some existing designs based on Strutt's original, for example <a href="https://www.lisaboyer.com/Claytonsite/epicyclicpage1.html">one by Clayton Boyer</a>, <a href="https://www.woodenclocks.co.uk/clock-33/">one by Brian Law</a> (without the paradox), and at two on GrabCad (<a href="https://grabcad.com/library/strutt-epicyclic-train-clock-1">1</a>, <a href="https://grabcad.com/library/william-strutt-epicyclical-geared-clock-my-wall-mounted-version-in-laser-cutting-plywood-design-1">2</a>).</p><p>The gear ratios work as follows. Let:</p><p></p><ul style="text-align: left;"><li>A = teeth on fixed sun gear</li><li>B = teeth on planet pinion</li><li>C = teeth on planet gear</li><li>D = teeth on inner side of ring gear</li><li>E = teeth on outer side of ring gear</li><li>F = teeth on escape pinion</li><li>G = teeth on escape wheel (not shown)</li><li>H = teeth on free (hour) sun gear</li></ul><div>The period of the planet carrier (and hence the minute arbor) divided by the period of the ring gear is 1+AC/BD. The period of the escape wheel divided by the period of the ring gear is F/E. We'll come back to the hour gear in a moment.</div><div><br /></div><div>In Strutt's design, A=66, B=8, C=68, D=144, E=168, F=6, G=34 and H=72. Thus, if the period of the planet carrier is 3600 seconds, the period of the ring gear is 3600/(1+(66*68)/(8*144)) = 735.3 seconds, and the period of the escape wheel is 735.3*6/168 = 26.26 seconds. As there are 34 teeth on the escape wheel, the period of the pendulum must be 26.26/34 = 0.772 seconds, implying the pendulum is about 14.8 cm (5.8 inches) long. This makes the mechanism suitable for a desk clock, as in the example shown in the Horological Times article.</div><div><br /></div><div>I don't fully understand how the Ferguson's paradox works, but I can give some hand-waving reasoning about why it gives the right timing. Essentially, each turn of the planet about the fixed sun (66 teeth) advances the free sun by its number of teeth, 72. This turn takes one hour, so in that time, the free sun has advanced by 72-66=6 teeth relative to the fixed sun. This is 1/12th of its total number of teeth, hence making it rotate once every 12 hours. Note that in order for the free sun to have the same diameter as the fixed sun, it must have a different module (ratio of diameter to number of teeth), thus breaking the normal rule for gears to engage correctly.</div><div><br /></div><div><b>Design decisions for a 3D printed version</b></div><div>I wanted to take this design and adapt it for 3D printing. The hardest part of this is finding a size which will work, by picking a suitable module for the gears. This then constrains almost everything else. We need to be able to print both a very small gear (escape pinion, 6 teeth) and to fit a very large one (ring gear, 168 outer teeth) on the print bed.</div><div><br /></div><div>There is one other constraint. The tips of the planet gear teeth must not come too close to the minute arbor:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEggFNuamlFwF6PX4aHGfDfrmwPzCoFTQfm0vt3KEKDX4kt3qZAYnPBmcTPdFFKZgCxmbPO9iAB_wFW1j1fwbXVAZdsy0-58cRdwLqzq7NvvDDGsUUxD-b3SvLHdzPnPhmEKdm7G/s705/capture_001_31102021_104822.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="660" data-original-width="705" height="300" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEggFNuamlFwF6PX4aHGfDfrmwPzCoFTQfm0vt3KEKDX4kt3qZAYnPBmcTPdFFKZgCxmbPO9iAB_wFW1j1fwbXVAZdsy0-58cRdwLqzq7NvvDDGsUUxD-b3SvLHdzPnPhmEKdm7G/s320/capture_001_31102021_104822.jpg" width="320" /></a></div><br /><div>The distance from the center of the minute arbor to the tip of the planet gear teeth is (A+B-C-2)m/2, where m is the gear module. This follows from the center of the planet and planet pinion being (A+B)m/2 from the center, and the outer radius of the planet gear being (C+2)m/2.</div><div><br /></div><div>At a module of 1.2, the ring gear is 204mm in diameter, and will just fit on the bed of a Prusa MK3S. The escape pinion is tiny at this modulus, with an outer diameter of just 9.6mm and teeth only about 1mm across. We actually do have some freedom to use a larger planet pinion, which in turn changes the size of the pendulum. For example, with 10 teeth (and hence 12 mm diameter), the pendulum needs to be 41cm long. You can somewhat compensate by adding more teeth to the escapement wheel: if we change it from 34 to 40 teeth, the pendulum needs to be about 30cm for a 10-tooth pinion.</div><div><br /></div><div>The spacing between the axis and the tip of the planet gear teeth is 2.4mm, meaning the minute arbor diameter must be under 4.8mm in a world where everything is perfectly sized. In practice, you have slightly more leeway as the printer will round off the very tips of the teeth, but you also need to allow for slight misalignments and wobble as the mechanism moves. There is one further issue associated with this. The free sun (shown in yellow) is loose on the minute arbor, so seen from the side it looks like this:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfLi3tTf2YSjOnyGCIQxfMQhINTh3ifxCgEm_GkdWB3rRMxWfGXEgq_wtFRt3rDBCy-2RoIZtpOtQq2Us-3kCI0uyyukRDsMsnJMD_kFqVsK3kLZLIjvTIs3H5cQDXDnGoCmA7/s1101/capture_002_31102021_110054.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="782" data-original-width="1101" height="227" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfLi3tTf2YSjOnyGCIQxfMQhINTh3ifxCgEm_GkdWB3rRMxWfGXEgq_wtFRt3rDBCy-2RoIZtpOtQq2Us-3kCI0uyyukRDsMsnJMD_kFqVsK3kLZLIjvTIs3H5cQDXDnGoCmA7/s320/capture_002_31102021_110054.jpg" width="320" /></a></div><br /><div>In this illustration, the minute arbor diameter is 2mm, about as small as possible. How do we keep the free sun in its position along the shaft? One option is to add a shaft collar just underneath it, rigidly attached to the shaft. Another would be to add a spacer, but its hard to find a diameter which can both be printed reliably and won't interfere with the planet gear. We could also use a piece of thin tube as a bushing; for example, a 2.5mm tube with a wall thickness of 0.225mm.</div><div><br /></div><div>Another possibility is to reduce the number of teeth in the planet gear. At 66 teeth, we have 3.6mm radial space instead of 2.4. At 64 teeth, we have 4.8mm space. The number of teeth on the inner side of the ring gear must decrease to compensate, and the pendulum needs to be slightly longer. Making this change in no way alters the Ferguson's paradox, as it is only the fixed and free suns and the planet pinion which participate in this. With 64 teeth, there is no need for a shaft collar and instead the planet carrier can be modified:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1j8v-007iehscI9TPOUz2-mvG1RfvZaKf7SADIo9VYgZaNmyy8JiEzsxbeZ3mE7SFW0ZW8kchvGm5tOIKWdkbpywURjgFNHZmef1PdUslUvY5CAJWvaqywHpL5IdpOcntAk65/s634/capture_004_31102021_154950.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="535" data-original-width="634" height="270" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1j8v-007iehscI9TPOUz2-mvG1RfvZaKf7SADIo9VYgZaNmyy8JiEzsxbeZ3mE7SFW0ZW8kchvGm5tOIKWdkbpywURjgFNHZmef1PdUslUvY5CAJWvaqywHpL5IdpOcntAk65/s320/capture_004_31102021_154950.jpg" width="320" /></a></div><br /><div>It is possible to use a 3mm minute arbor in this configuration. The inner ring gear now has 140 teeth and a slightly longer rotational period. With the 6/34 escapement, the pendulum would need to be about 1 cm longer than before.</div><div><br /></div><div><b>Tooth profiles</b></div><div>Most gears use an involute tooth profile: the classic shape with a narrowed "waist". Cycloidal gears are an alternative that has been used in clocks, and it works well for 3D printing as the teeth have straight sides with no waist. Once the teeth are above a certain size, the sides are parallel and so fewer small gap fill movements are required from the printer. For small teeth, the sides are not parallel, though it is possible to adjust a bit from the strict profile to avoid them becoming too fragile. Fusion 360 and Blender both have add-in gear generators, but they only work for involute teeth. I was able to find <a href="http://www.hessmer.org/blog/2012/01/28/cycloidal-gear-builder/">a cycloidal gear generator as downloadable software</a>. There is an online version as well, but I prefer the downloadable version as it can generate SVG files, which are more convenient for converting into sketched in Fusion 360. The SVGs need to be scaled to the correct size after loading them up. One thing the software lacks is a way of generating the inner teeth for the ring gear. Some people suggest creating an outer gear and then using it to cut away the inner part. It is approximately correct for involute teeth, but does not work for cycloidal ones. My approach was to load the SVG file, then flip the lines making up one tooth about a chord drawn on the pitch circle:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi39S3kPuTewFKpkvj5DcolZIQkNg09YuM02EA-RkNV0LT3lXEgizF9VKtp56yN9aHebkUx9_mr1IZR_a0BsFfH4tSMBUh5AGfejpjfq-jVfAHWr8sRYFWKpShkwQJ1-gFjwH_t/s462/capture_003_31102021_145933.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="340" data-original-width="462" height="235" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi39S3kPuTewFKpkvj5DcolZIQkNg09YuM02EA-RkNV0LT3lXEgizF9VKtp56yN9aHebkUx9_mr1IZR_a0BsFfH4tSMBUh5AGfejpjfq-jVfAHWr8sRYFWKpShkwQJ1-gFjwH_t/s320/capture_003_31102021_145933.jpg" width="320" /></a></div><br /><div>Another problem with the output of the gear generator is that the arcs at the base of the teeth do no quite line up with the edges of the teeth. I solved this by adding a base circle to the teeth. To generate the gear in Fusion 360, I extruded one tooth, copied it with a circular pattern and then added the body of the gear using the base circle.</div><div><br /></div><div><b>Drive and timing</b></div><div>Strutt's design used a pinion plus escape wheel for the timing and was driven by a spring coupled to the minute arbor. You could also drive the minute arbor with a weight, if the clock is configured as a wall clock. The gears move quite freely and so could also be driven by a stepper motor in a similar way to <a href="https://www.youtube.com/watch?v=xMBCaaJSsMM&ab_channel=DavidElworthy">Steve Peterson's desk clock</a>. Another option is to use an electromagnetic pendulum. I can't find any examples of exactly this, though there is <a href="http://woodenclockspot.blogspot.com/p/epicyclic.html">a somewhat related design by Nigel Climpson</a>.</div><div><br /></div><div><b>Prototype</b></div><div>I wanted to validate that the basic mechanism works before going further. It's a bit hard to video it (not enough hands!), but this clip shows that it moves quite smoothly.</div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/sYEGMaVHaFE" width="320" youtube-src-id="sYEGMaVHaFE"></iframe></div><br /><div class="separator" style="clear: both; text-align: center;"><br /></div><div><br /></div><div>If you look carefully, you can see the hour wheel advancing. For the next stage, I need to settle on the drive mechanism. The planet carrier also needs a slight redesign so that the circular piece counterbalances the planet gear.</div><p></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-50512037230846178672021-10-26T19:09:00.003-07:002021-10-26T20:52:31.449-07:00Cycloidal gears in Fusion 360<p>Fusion 360 has tools for creating involute gears, including its own spur gear add-in and GfGearGenerator, and they work well. However, if you want cycloidal gears, it's not so easy to find something that works. Here's one approach, in case this turns out to be helpful to anyone else.</p><p></p>Start by generating the gear in DXF form using <a href="http://hessmer.org/gears/CycloidalGearBuilder.html">Rainer Hessmer's Cycloidal Gear Builder</a>. Make sure to use the highest quality level. It's useful to include a hole in the middle so you can identify the center. Download the DXF file. If you load this DXF into Fusion 360 (Design > Insert > Insert DXF) you will get an unhelpful error message. The DXF file isn't in a form that Fusion 360 can handle and we need to fix it.<div><br /></div><div>You can fix the DXF by importing into FreeCad and then exporting it again. Another option is to import it to Inkscape and save it with "Save As". The DXF should then import into Fusion 360. However, if the gear is large, Fusion 360 may sit for hours processing it. It might never finish. Selecting "One sketch per layer" when inserting it sometimes helps, but generally does not. So another option is save it as a SVG from Inkscape and insert that instead. It's still slow, but does work. If you are lucky, you might be able to extrude the result and create the gear from it. Or sometime Fusion 360 will just abruptly exit.</div><div><br /></div><div>The Cycloidal Gear Generator is supposed to have an option to output to SVG but it was missing when I looked for it. However, instead you can download a desktop version of the app from <a href="https://code.google.com/archive/p/drh-horology/downloads">here</a>. This will give you a SVG with much better segments. Note that you have to specify that you want a pinion. In the web version you can omit it. The desktop version raises an exception if you try. The result will load into Fusion 360, but it won't work as the segments don't join into a closed curve. However, we can use the sketch as a starting point.</div><div><br /></div><div>First note that the imported SVG won't have the right size. We need to scale it. To find the scale factor measure an element of known size. For example, if you created a 6mm hole in the middle of the gear, measure its actual diameter and scale by 6 divided by this. Measuring the radius is usually easiest, and so then you would scale by 3 divided by the measurement. To scale the whole sketch, exit sketch mode, go to Modify>Scale, select the sketch from the browse list, and enter this factor.</div><div><br /></div><div>Now we want to go into edit sketch and delete everything except for the center hole and one tooth. The tooth will consist of two lines and two arcs. You ought to be able to create a circular pattern with these and the arc joining them to the base of the next tooth, but you don't get a closed path if you do. The problem is that the exact end points of the lines aren't right. So change everything to a construction line (with x), then change the two lines and two arcs back. Create a center circle with circumference on the ends of the lines. Now create a circular pattern with the two lines and the two arcs about the center of the gear, with a number of elements equal to the number of teeth you want. You should now be able to exit sketch mode, select all the teeth and the circle you just created, and extrude your gear.</div><div><p></p></div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-27714617231192861792021-10-24T09:03:00.002-07:002022-04-30T11:45:50.785-07:00The Daisy Clock<p>One of the designs in the book <i>Making Wooden Gear Clocks</i> is for an electromagnetic gear clock driven by a simple and baffling mechanism. I took the design and adapted it for 3D printing; as with some of the other clocks, I won't publish my design as the copyright status is unclear. Here is the clock:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgfzVXkIANRAukIrbomdDWRTpsfS1HWCBbu6KOKkDF29cXqsfR1dOxrULEBUKmBw15pgKGNCDjdcj30KyIWmEwidZ_BwbFHk2X6Bq5b-rfZFKzib5zh1cBKGJclkRCSQRhll9Yh/s4032/PXL_20211024_154236114.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgfzVXkIANRAukIrbomdDWRTpsfS1HWCBbu6KOKkDF29cXqsfR1dOxrULEBUKmBw15pgKGNCDjdcj30KyIWmEwidZ_BwbFHk2X6Bq5b-rfZFKzib5zh1cBKGJclkRCSQRhll9Yh/s320/PXL_20211024_154236114.jpg" width="240" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFu3X6T7lCd5lm67zdBnJzDLQudspYtN2pfTejTMKaTvFiyRslHAlndHuFlejspOYzlh911O0j8g4fuN4uo98j5HTViNxStxthIG0HxGH6vqUqZeBs4QDlmzAR_sLv8LEPMjQE/s4032/PXL_20211024_154240098.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFu3X6T7lCd5lm67zdBnJzDLQudspYtN2pfTejTMKaTvFiyRslHAlndHuFlejspOYzlh911O0j8g4fuN4uo98j5HTViNxStxthIG0HxGH6vqUqZeBs4QDlmzAR_sLv8LEPMjQE/s320/PXL_20211024_154240098.jpg" width="240" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/ENzw7DWsbcI" width="320" youtube-src-id="ENzw7DWsbcI"></iframe></div><br /><div class="separator" style="clear: both; text-align: center;"><br /></div><p>The clock works as follows. The pendulum is driven electromagnetically by means of a magnet in the end of the pendulum and a coil in the base. The coil detects when the magnet comes close and then sends a pulse to drive it on its way. The pendulum drives a cam with two pawls on it. This in turn engages with a toothed wheel and advances it once per second. The principles thus far are similar to the Thriecan clock described in a previous post.</p><p>The minute wheel is also a toothed wheel, with the opposite orientation to the seconds wheel. A small metal rod near the middle of the seconds wheel engages with the teeth of the minute wheel and advances it once per minute.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFyuiiYbXg1g-TuniLWZakjyPhdmzilXrOISnrIUvLBmbvKGbV-LP116mIV0Mv7AsyhvdJt_5FqiDIjqqcxHcPBbhOSsk75JGMWjHQTc-7L5Z-zInxqoe4c9Uu6A0rwmWhDQpZ/s4032/PXL_20211024_154245785.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFyuiiYbXg1g-TuniLWZakjyPhdmzilXrOISnrIUvLBmbvKGbV-LP116mIV0Mv7AsyhvdJt_5FqiDIjqqcxHcPBbhOSsk75JGMWjHQTc-7L5Z-zInxqoe4c9Uu6A0rwmWhDQpZ/s320/PXL_20211024_154245785.jpg" width="240" /></a></div><br /><p>There is also a pawl for the minute wheel to prevent it falling back. The minute wheel is tightly attached to an arbor which also carries the minute hand.</p><p>Now we get to how the motion of the minute wheel is divided down 12:1 to the hours motion. This is done by means of the daisy wheel. The daisy (or daisy wheel) motion was invented around 1830 by Aaron Dodd Crane. The wooden clocks book does not credit the invention or explain how it works. There is a little more information in Philip Woodward's book <i>My Own Right Time</i>.</p><p>The daisy wheel has 11 petals and 11 notches between the petals. A device ("tri") with 3 arms interacts with the daisy wheel by means of pins mounted on the ends of the arms. A rod attached to the daisy holds it loosely in place in the frame, allowing this movement while preventing it from just rotating with the tri. Woodward mentions that the number of arms and pins is not critical. The hour hand is mounted on the tri. The key to this is that some parts of the mechanism are mounted eccentrically to the minute arbor and so the whole system operates in a manner similar to epicyclic gears. I will have more to say about that eccentric mounting in a moment, but first I want to say that I simply do not understand this in any detail. Every time I try to reason it through, my brain breaks. The explanation in Woodward and in another work as well as several YouTube videos do not make it any clearer to be and mostly they end up with a statement along the lines of "you have to see it to believe it". It clearly does work. I just can't understand how, and why having 11 notches on the daisy leads to a 12:1 reduction.</p><p>I've been a little evasive about exactly what is eccentric, and the reason for this is that I think the design in <i>Making Wooden Gear Clocks</i> is incorrect. In the design as shown in exploded form in the book, on the accompanying plans, and in the photos showing it being assembled, the daisy is mounted co-axially on the minute arbor. A part called the tri excentric in the book is also mounted on the arbor, such that its axis of rotation is offset from the axis of the minute arbor. The tri rotates about this offset axis. Thus the parts look like this:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLXH_bLMEwif3O5peDujS1OA_0QECmAV5bpf4_ecn2wlhyphenhyphenxMHrFH6R8JxFhBWJWr9OY6Dg7Rs0t0HTlp_E4iCSpd088w7gpJy3pg9ncYLX4sWUXPZj4Z9_68wUGUwkd0M-t1-4/s4032/PXL_20211023_194501776.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3024" data-original-width="4032" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLXH_bLMEwif3O5peDujS1OA_0QECmAV5bpf4_ecn2wlhyphenhyphenxMHrFH6R8JxFhBWJWr9OY6Dg7Rs0t0HTlp_E4iCSpd088w7gpJy3pg9ncYLX4sWUXPZj4Z9_68wUGUwkd0M-t1-4/s320/PXL_20211023_194501776.jpg" width="320" /></a></div><br /><p></p><div class="separator" style="clear: both; text-align: left;">The daisy therefore stays stationary while the tri and hence the hour hand rotate around an axis which is not coincident with the minute axis. As a consequence the hour hand moves off-center to the minute hand. You can see this in the following video, in which I turn the minute wheel by hand.</div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/vkYA83iOVZU" width="320" youtube-src-id="vkYA83iOVZU"></iframe></div><br /><div class="separator" style="clear: both; text-align: left;">I have not been able to find any video of other builds of this clock which show it running for more than a few seconds, which is not long enough to see the problem. Consulting Woodward, Shelley's book on Crane, and several YouTube videos (<a href="https://www.youtube.com/watch?v=evOtMbUeLic&t=1s&ab_channel=KenKuo">example 1</a>, <a href="https://www.youtube.com/watch?v=RVWd-QedUTY&ab_channel=appropriatedesign">example 2</a>, <a href="https://www.youtube.com/watch?v=fdb7_VCaiOE&ab_channel=GadgetBuilder">example 3</a>) show that this design is simply wrong. The tri and hour hand should rotate on the same axis as the minute arbor. To quote from Woodward:</div><blockquote style="border: none; margin: 0px 0px 0px 40px; padding: 0px;"><div class="separator" style="clear: both; text-align: left;"><i>the daisy wheel is mounted loosely on an eccentric collar rigidly fixed on the central arbor of the clock.</i></div></blockquote><div class="separator" style="clear: both; text-align: left;">It is the daisy that should be eccentric to this axis, and although the daisy does not rotate, it does move a little to accommodate this motion. It's hard to believe that the author of the design and the editors of the book failed to notice this. As far as I can tell, they have not acknowledged the error or published any errata for the book.</div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">After initially building the clock according to the published design, I reworked the daisy and tri to the correct configuration. Here is how the hour hand motion looks now:</div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/ekIQwiz2I4A" width="320" youtube-src-id="ekIQwiz2I4A"></iframe></div><br /><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">The reworked parts look like this:</div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjO4wyYrbfMI6WxP4fNWSWpD67pMa1SRnlFok1KzAEh2BAbS5R2zUTZKNTTJbKbESF9nS2Pq3RktpNAjrSRXnXnt9EnDXKYaeO61Y2ikeo6PLgA0SmADYhm_kmaYOD2b1NGcvrC/s4032/PXL_20211024_152922417.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3024" data-original-width="4032" height="240" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjO4wyYrbfMI6WxP4fNWSWpD67pMa1SRnlFok1KzAEh2BAbS5R2zUTZKNTTJbKbESF9nS2Pq3RktpNAjrSRXnXnt9EnDXKYaeO61Y2ikeo6PLgA0SmADYhm_kmaYOD2b1NGcvrC/s320/PXL_20211024_152922417.jpg" width="320" /></a></div><br /><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">As with some of the earlier clocks, I view this as a clock demonstrator rather than a practical timepiece. I wanted to see how the mechanism worked. For this reason, I didn't spend a lot of time on the frame and base. I quite like the minimalistic "candlestick" design. I thought it might be too unstable, but it seems OK.</div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">I used my own electronics in this clock, detailed in an earlier post. One unexpected issue I had was this: the clock was working fine when I had it attached to a piece of plywood for testing. Then when I mounted it on its base, the pendulum became very unstable. It would jump all over the place. This turned out to be because the magnet was attracted to the screws in the corner of the case and to the USB connector. I solved this by using weaker magnets and moving them a little lower to compensate.</div><div class="separator" style="clear: both; text-align: left;"><br /></div><br /><div class="separator" style="clear: both; text-align: center;"><br /></div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-20800440778571795192021-10-13T13:20:00.001-07:002021-10-13T13:20:25.658-07:00Driver for an electromagnetic pendulum<p>In a previous post, I described some experiments with circuits for driving an electromagnetic pendulum. The results were not very satisfactory, and for the Thriecan clock, I ended up using a commercial module. I have since revisited this, and now have something I am happier with. To recap: the pendulum contains a magnet. As it approaches the center of its swing, a sensor detects its presence, and then energizes a driver coil to impart some momentum to the pendulum. Ideally, you use one coil as both the sensor and driver. The circuit I present here uses an Arduino and a small number of discrete components.</p><p><b>Some initial experiments</b></p><p>In the first attempt, I was unable to get a strong signal from a coil: only a few millivolts. This is probably because of the geometry of the coil, which had a narrow diameter but was quite long (about 25mm), based on the one in the instructions for the Toucan clock. It is better to have a shorter, fatter coil, so that more of the winding is close to the magnet as it passes by. I rewound the coil on a bobbin with a 6mm inner diameter and a length of 10mm. I did not count the number of turns or measure the length of wire. Based on its resistance (35 ohms) and the resistance per unit length for 32 AWG magnet wire, it is around 60m. The winding is about 30mm in diameter.</p><p>I wanted to know how much difference the specific magnet made, so I constructed a pendulum with the magnet on the end of a 300mm brass rod and measured the voltage when the pendulum was dropped from a known position. The magnets I had lying around were:</p><p></p><ul style="text-align: left;"><li>20mm x 4mm N38</li><li>12mm x 3mm N35 (I think)</li><li>12mm x 3mm N42</li><li>10mm x 3mm N52</li></ul><div>All but the first gave about 0.3V. If you add a second or third one, this goes up by 0.1V per additional magnet. The 20mm one gave 0.5V or around 0.65V with two. I was a bit surprised that the grade of magnet didn't make a difference, as each unit of N rating is supposed to correspond to an extra 1% in magnetic field strength (or something like this).</div><div><br /></div><div>The distance between the magnet and the coil also makes a difference. My test setup didn't allow me to change it much, but an increase of distance between the coil and the magnet from about 3mm to about 6mm dropped the voltage by half.</div><div><br /></div><div><b>The circuit</b></div><div><b><br /></b></div><div>Here is the circuit. I'll explain the ideas behind it in a moment.</div><div><b><br /></b></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_cnuX5RupzV32T1a_TVNj9og7NqnyVyfv7lAId9H6OUpzY3fzTmqoYRnv7rh1925UJjA5TKn2pURVpYL-QK9laDqGND-wYHlkiWk2Z-CQnE1EtEEQ5doMzv39uY9W3JwjtFac/s520/circuit.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="340" data-original-width="520" height="209" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_cnuX5RupzV32T1a_TVNj9og7NqnyVyfv7lAId9H6OUpzY3fzTmqoYRnv7rh1925UJjA5TKn2pURVpYL-QK9laDqGND-wYHlkiWk2Z-CQnE1EtEEQ5doMzv39uY9W3JwjtFac/s320/circuit.png" width="320" /></a></div><div>(Diode: 1N4001. Transistor: PN2907.)</div><div><br /></div><div>The voltages I measured aren't enough to register as a digital signal when connected to an Arduino and are maybe too low to switch a transistor which could be attached to a digital input. An alternative is to use an analog input of the Arduino and then set a threshold in code based on the analog reading. With a resolution of about 5mv per step, we should be able to do this. A reading of even 0.1V would be detected as a value change of 20 on the analog input.</div><div><br /></div><div>If you search the web for advice on connecting a coil as a sensor to an Arduino, there is a lot of unclear (and possibly misleading) information. The main concern is that transients from the coil could exceed the input voltage range of the Arduino and so damage it. Various solutions involving voltage dividers or Zener diodes can be found. I don't think this is necessary. The Arduino inputs have protection diodes which limit the voltage to just above 5V and just below 0V. The issue with the protection diodes is that they can only handle a limited amount of current. 1mA might be OK, 100uA definitely is. More than that would likely burn them out. In the circuit above, the flyback diode on the coil should eliminate most of the risks, but to be sure, I designed the circuit to allow for a 10V swing. In this case, with a 100k resistor on the analog input, the current would be 100uA and we are OK. Relying on the protection diodes is something that people argue about on various forums, leading to some of the other solutions. An <a href="https://www.microchip.com/content/dam/mchp/documents/OTH/ApplicationNotes/ApplicationNotes/Atmel-2508-Zero-Cross-Detector_ApplicationNote_AVR182.pdf">application note from Atmel</a> has an example in which an analog pin is connected safely to mains at 110-240V AC. Also take a look at <a href="https://electronics.stackexchange.com/questions/35807/how-would-i-design-a-protection-clipper-circuit-for-adc-input">this</a>.</div><div><br /></div><div>There is one further issue with using the analog input. The Arduino datasheet recommends that the input impedance to analog pins should be 10k or less, and we want to use 100k. Looking into this in more detail, the reason appears to be that the analog to digital converter works by charging a capacitor internally and them sampling its voltage. The internal capacitor is 14pF and it should be charged in 6us or less at standard sampling rates. With a 100k external resistor, we have a time constant of 1.4us, so we should be OK.</div><div><br /></div><div>The remaining input element is the 10uF capacitor. It largely gets rid of noise and ringing on the input without slowing down the signal too much. Looking at the signal on an oscilloscope, there is still a small and short duration spike at an acceptable level. With no capacitor at all, there are spikes for about ten milliseconds before the circuit settles down.</div><div><br /></div><div>On the output side, we simply drive a transistor from a digital pin. When the pin is low, the transistor turns on and the coil is energized. The sensor can't be read at the same time, and that's OK as we don't need to. The flyback diode helps to protect the transistor when it turns off and the field in the coil collapses.</div><div><br /></div><div>In previous experiments, I found that I needed external power to get enough drive in the coil, mainly due to use a coil with less good geometry. For this version, the 5V output of the Arduino worked fine. Its Vin can also be used if a higher voltage or current is needed. I experimented with an Arduino Uno, but will move to using a Nano soon.</div><div><br /></div><div>The code is similar to the version I gave before, namely:</div><div><ul style="text-align: left;"><li>read the sensor</li><li>when it exceeds a threshold (20), wait (10ms)</li><li>turn on the coil (200ms)</li><li>turn off the coil, and wait a little longer (10ms)</li><li>keep going</li></ul><div>I still have to tune the exact timings and the threshold. These values give a very strong swing to the pendulum. Currently I am not using a weight bob or tuning to 1s per cycle, and this may affect the timing and possibly the voltage needed to drive the coil.</div></div><div><br /></div><div>I've not fitted this to the Thriecan clock. My intention is to use it for a possible future design.</div><div><br /></div><p></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-87973854930514332392021-10-10T15:30:00.002-07:002021-10-10T15:30:30.695-07:00The Thriecan Clock<p> The Thriecan Clock is a modified version of <a href="https://www.lisaboyer.com/Claytonsite/toucanpage.html">Clayton Boyer's Toucan clock</a>, adapted for 3D printing. The key feature of this clock is a electromagnetic pendulum. There is a magnet attached to the end of the pendulum and a coil hidden in the base. As well as providing the timing, the pendulum also provides the energy to drive the clock. As the pendulum approaches the vertical position, the electronics attached to the coil senses the magnet and applies a pulse to the coil. This pushes the magnet and hence the pendulum away and the process continues. The top of the pendulum is attached to an arbor and this turns a cam with two pawls. One pawl, called the pick-up pawl, pushes on the escape wheel. The other pawl then holds the escape in place while the pick-up pawl moves back for the next cycle. The remainder of the clock is a standard gear train to divide the rotation of the escape wheel down to minutes and hours.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEis256z7stc4Ko3gK8dUs4G6ZYgo3Zo3EHW9eFxZOqgqtK1wvUV_s0AnAeip1WN9JjdtOggEugVo3Rc7nrLvv8bSKY0LcSf6gqFC53LMWwDdBP-MHgCSL0QTrMIR1YhhIEFpEgf/s4032/PXL_20211010_204027354.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEis256z7stc4Ko3gK8dUs4G6ZYgo3Zo3EHW9eFxZOqgqtK1wvUV_s0AnAeip1WN9JjdtOggEugVo3Rc7nrLvv8bSKY0LcSf6gqFC53LMWwDdBP-MHgCSL0QTrMIR1YhhIEFpEgf/s320/PXL_20211010_204027354.jpg" width="240" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi05yC9pkaUmudCdd2Dfk4gy2h_f0DPnss5GkgJxEGcjuYzAHGomDeHiMCI7R4Q9apibNmrk72i1mgyylYGxTXqwo9x-mcSjRolV9ZiPyrhG-NAY49TrlSUVkmmiyhqcLSaIVRx/s4032/PXL_20211010_204126194.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi05yC9pkaUmudCdd2Dfk4gy2h_f0DPnss5GkgJxEGcjuYzAHGomDeHiMCI7R4Q9apibNmrk72i1mgyylYGxTXqwo9x-mcSjRolV9ZiPyrhG-NAY49TrlSUVkmmiyhqcLSaIVRx/s320/PXL_20211010_204126194.jpg" width="240" /></a></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-ayrDP2gwgxIhpIEhe-f9hyphenhyphenzOsqVi-sI9ZnE9c9_aczm6qevAUzFKS04VqdkCkZmjgl3VU2T5tM_tzdfy03M5yoP8PcH7t6i6Cx6edjnoWLYPqjwjotsv5SjesKnR-nWPrewi/s4032/PXL_20211010_204207316.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="4032" data-original-width="3024" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-ayrDP2gwgxIhpIEhe-f9hyphenhyphenzOsqVi-sI9ZnE9c9_aczm6qevAUzFKS04VqdkCkZmjgl3VU2T5tM_tzdfy03M5yoP8PcH7t6i6Cx6edjnoWLYPqjwjotsv5SjesKnR-nWPrewi/s320/PXL_20211010_204207316.jpg" width="240" /></a></div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/3q52xYScQOI" width="320" youtube-src-id="3q52xYScQOI"></iframe></div><br /><div class="separator" style="clear: both; text-align: center;"><br /></div>The version you see here is not quite final. I am going to replace the battery pack with power connector so I can connect it or a different power source. There is enough room to locate the battery pack in the base, but it disrupts the operation by attracting the pendulum. There's also a few screws sticking out while I make final adjustments and I will then replace them with shorter ones.<p><b>Adapting the design</b></p><p>The original design was intended to be made out of wood. You can see many examples on the <a href="https://www.youtube.com/watch?v=zTd3JBE8kPo&list=PL8Ko-UkDoXedcWjUZAp8JdwAnnEFvZ31V&ab_channel=Bandman7020">Toucan clocks YouTube channel</a>. I bought a copy of the plans in DXF format and loaded them up into Fusion 360 to provide a starting point for the sketches. For parts where the dimensions were critical, I used these sketches directly, and for others I either adapted them (for example, the cam) or replaced them entirely (for example the weight bob). The original design used 3/8 inch arbors, and I replaced these with 3mm ones. Instead of printing separate gears, connectors and pinions and then gluing them together, I merged them into a single part. This is something which works nicely for 3D printing, but it difficult or impossible in woodwork. I undersized many of the holes for the arbors and for the pendulum shaft and drilled them out to either a tight fit or a loose one. I've not always been successful in getting good tight fits and so where possible I also provided holes for set screws.</p><p>One of the hardest parts to adapt was the frame. It is much too big to fit on the printer bed. It's possible to split up large pieces like this and then glue or otherwise connect them. However, I didn't like where the splits ended up so I changed the shape of the frame. It still needs to be split into three pieces: the main part of it, the left foot, and the curve reaching down to the right foot. You lose the nice curve on the left hand side of the original design by doing this. The joins are hidden behind the dial on the left and where the arc on the right joins the vertical part. In each case, as well as gluing the parts, there are some metal pins joining them. These help keep the parts aligned while the glue sets and provide a little extra strength. The dial is also slightly smaller, and has a central bar to help support one arbor and the hour wheel. It's held on to the frame with two M3 screws. I didn't really think ahead here, so I ended up having to use 45mm screws with a bit of padding behind the frame to get the length just right.</p><p>One reason for wanting to try this specific design was to see how easy it is to start with a plan designed for woodworking and adapt it for 3D printing. It worked out somewhat well. The process was a bit hindered by the ways the plans are supplied: the DXF is a single gigantic file some parts of which are actual plans, and some parts of which are descriptive text, assembly diagrams and other auxiliary information. It seems an odd way of doing things. Fusion 360 gets a bit heated when you load all this in, and so a fair amount of initial pruning was needed. I'm also a novice with Fusion 360, so the way I did some things might not be best.</p><p><b>The pendulum</b></p><p>The pendulum is a 2mm brass rod with the magnet holder as the bottom and the weight bob around the 25cm mark. Adjusting the position of the weight is a bit fiddly as it involves loosening the screw underneath it, and sliding it up or down. The bob holds quite tightly to the shaft so adjustment can be down without tightening the screw until it is in its final position. The weight itself is a few M3 screws in the shiny little bucket.</p><p>The pendulum is connected to the cam with a 3mm brass shaft. This is a problematic part of the design, as the weight of the pendulum is greater than that of the cam and pawls, causing the shaft to tilt to the back. There are a few ways this could be fixed; perhaps a counterweight on the front, or a longer support glued to the back of the frame. Another option would be to move everything in front of the from forward and lengthen the shaft. For now, it works OK as it is.</p><p><b>One tooth or two?</b></p><p>Looking at the examples of the Toucan clock on YouTube, there are two different philosophies about the position of the pick-up pawl and the stop pawl at the point where the pick-up pawl starts to push on the escape wheel. They can either be on adjacent teeth like <a href="https://youtu.be/WpSnuQ5CzYw?t=13">this</a>, or separated by one tooth like <a href="https://youtu.be/zTd3JBE8kPo?t=87">this</a>. The clock runs either way, and you can set the way it works by adjusting the angle between the pendulum and the cam. It may make some difference to the required swing of the pendulum. Looking at the first 10 videos on the YouTube list, I saw 8 were adjacent (the Toucan closes its beak) and 2 were separated (the Toucan eats with its mouth open). I went for adjacent, which sets the cam a bit anticlockwise from the pendulum.</p><p><b>Driving circuit</b></p><p>I experimented with various driving circuits. As mentioned in a previous post, I had no success with getting a 1 or 2 transistor circuit to work, and after fiddling around for a long time, I wasn't happy with any of the other options I tried. In the end, I decided to buy a ready made module from <a href="https://carveshop.com/electronics/">carveshop</a>. It works well, but is a little pricy. I plan to spend some more time looking into this, in part because I have a second electromagnetic pendulum clock I would like to try.</p><p><br /></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com4tag:blogger.com,1999:blog-8371051.post-90644614741893359802021-10-03T15:50:00.001-07:002021-10-09T11:01:32.873-07:00An electromagnetic pendulum<p> For a future clock project, I would like to construct an electromagnetic pendulum. The pendulum has a magnet at its tip, and base contains a coil of thin wire. We aim to detect when the pendulum is approaching, and then turn on the coil for a short time to add extra energy. This can be done by turning on the coil to attract the magnet before the pendulum reaches the center (vertical), or waiting until it has passed the center and turning on the coil to repel it.</p><p>There are many different ways of doing this, and it was used in commercial clocks before electronic movements took over. The German-made Kundo clocks are one example. If you look on the web, you will find many articles about electronic pendulums, whether for clocks or just as toys, with a variety of different circuits. One of the best descriptions is <a href="https://sound-au.com/clocks/kundo.html">Kundo battery clocks</a> by Rod Elliot, with several possible circuits and a lucid explanation of how they each work. There is a 2 coil, 1 transistor design, used in <a href="https://www.lisaboyer.com/Claytonsite/toucanpage.html">Clayton Boyer's Toucan clock</a>, and two variants of a 1 coil, 2 transistor design from the Kundo clocks themselves. In another article on the same site, Rod Elliot notes that there is some trial and error in getting these circuits going. After playing around for a few days without getting to anything reliable, I agree. I also found a site with a very similar circuit and a comment thread full on people saying how they never managed to get it to work. I'm not sure why I had so much difficulty. I know that for a few components (capacitors mainly), I didn't have the exact values and had to come up with a substitute. I tried out several different coils that I had around. Some didn't produce enough voltage to turn on the transistors. They would need more turns or more cross-sectional area, both of which affect the induce voltage. Others could clearly turn on the transistors but didn't impart enough energy the the pendulum.</p><p>There are other solutions, both analog or digital. One analog option is to replace the transistors with two or more stages of op-amps. You can then tune the sensitivity of the triggering better, and also add some delay before the pulse to the coil happens. Other solutions use a simple microprocessor like a PIC, or a TI chip.</p><p>I decided to go with a simple and highly controllable solution. I had some <a href="https://www.amazon.com/Effect-Magnetic-Sensor-Arduino-MXRS/dp/B085KVV82D/ref=sxin_13_trr_306929011_0?crid=28MDVNTC03D6K&cv_ct_cx=hall+effect+sensor&dchild=1&keywords=hall+effect+sensor&pd_rd_i=B085KVV82D&pd_rd_r=ed41d65c-824d-4d4d-b0d8-ba0a0646d561&pd_rd_w=UDJFR&pd_rd_wg=2Nfcv&pf_rd_p=4593e596-538b-4994-84c3-9cd98dccbfa6&pf_rd_r=04NHHZ0SHPTAK9YPJ9YE&qid=1633299663&sprefix=hall+effect%2Caps%2C227&sr=1-1-5519553e-2baa-451e-af83-b0156e5c6669">KY003</a> Hall effect sensor boards in my stock of parts, and so I just connected one to an input pin on an Arduino. The Arduino can't drive the coil directly, so I hooked up an output pin to a transistor, like this:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVLQJm_DkIgCRL4rrWZ3C60gQryuE6yBpPH6_ukRZE8aSKjfsEbAuYo7TQ80FEQavsZ3uSIRJzfYcKMFeoKbCVKCp9yYiZp5xXxM9Gx-n4WPeQWQSRxauIIKSVR9nd6OnIA1ku/s300/circuit.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="220" data-original-width="300" height="220" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVLQJm_DkIgCRL4rrWZ3C60gQryuE6yBpPH6_ukRZE8aSKjfsEbAuYo7TQ80FEQavsZ3uSIRJzfYcKMFeoKbCVKCp9yYiZp5xXxM9Gx-n4WPeQWQSRxauIIKSVR9nd6OnIA1ku/s0/circuit.png" width="300" /></a></div>The transistor is a PN2222, and the Arduino output pin connects to the 22k resistor.<div><br /></div><div>The code is quite simple:</div><div><ul style="text-align: left;"><li>wait until the Hall effect sensor turns on.</li><li>wait a while to allow the pendulum to reach the center.</li><li>energize the coil for a while.</li><li>check the Hall effect sensor has turned off (in case we are still within range).</li></ul><div>The pendulum itself if a 30cm brass rod. I want a period of about 1 second, so there is a weight around 25cm from the pivot. The magnet is at the end. The delay after detecting the sensor should be long enough for the pendulum to reach or just pass the center. If the angle of the pendulum at its extreme is P, and the angle at which we detect the sensor is S, then the delay should be arccos(S/P)/6.28, to a first approximation. The 6.28 comes from the angular frequency being 6.28 radians/second for a 1 second pendulum. See <a href="https://www.acs.psu.edu/drussell/Demos/Pendulum/Pendulum.html">here</a>. None of this is exactly right, as it assumes a small angle for P, whereas I actually see around 20 degrees in each direction. It also does not allow for extra energy being added to the system. But it will do to get roughly the right values.</div><div><br /></div><div>This is the prototype working. It needs a small nudge to get going:</div><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="266" src="https://www.youtube.com/embed/UYYWwT-UJ6k" width="320" youtube-src-id="UYYWwT-UJ6k"></iframe></div><br /><div>Here's the code. Note this is a prototype and might change before the final version.</div><div><br /></div><!--HTML generated using hilite.me--><div style="background: rgb(255, 255, 255); border-color: gray; border-image: initial; border-style: solid; border-width: 0.1em 0.1em 0.1em 0.8em; border: solid gray; overflow: auto; padding: 0.2em 0.6em; width: auto;"><table><tbody><tr><td><pre style="line-height: 125%; margin: 0px;"> 1
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<span style="color: #888888;">//</span>
<span style="color: #888888;">// Detect the magnet with hall effect sensor on this pin...</span>
constexpr <span style="color: #333399; font-weight: bold;">int</span> hall_sensor <span style="color: #333333;">=</span> <span style="color: #0000dd; font-weight: bold;">3</span>;
<span style="color: #888888;">// ... then wait this many milliseconds ...</span>
constexpr <span style="color: #333399; font-weight: bold;">int</span> detect_to_activate_delay <span style="color: #333333;">=</span> <span style="color: #0000dd; font-weight: bold;">23</span>;
<span style="color: #888888;">// ... then energise this output pin ...</span>
constexpr <span style="color: #333399; font-weight: bold;">int</span> output <span style="color: #333333;">=</span> <span style="color: #0000dd; font-weight: bold;">7</span>;
<span style="color: #888888;">// ... for this many milliseconds ...</span>
constexpr <span style="color: #333399; font-weight: bold;">int</span> activation_duration <span style="color: #333333;">=</span> <span style="color: #0000dd; font-weight: bold;">200</span>;
<span style="color: #888888;">// ... with this much slop in milliseconds when checking the sensor is out of range.</span>
constexpr <span style="color: #333399; font-weight: bold;">int</span> sensor_cooldown <span style="color: #333333;">=</span> <span style="color: #0000dd; font-weight: bold;">10</span>;
<span style="color: #888888;">// Use this pin for LED.</span>
constexpr <span style="color: #333399; font-weight: bold;">int</span> led <span style="color: #333333;">=</span> <span style="color: #0000dd; font-weight: bold;">13</span>;
<span style="color: #333399; font-weight: bold;">void</span> <span style="color: #0066bb; font-weight: bold;">setup</span>()
{
pinMode(led, OUTPUT);
pinMode(output, OUTPUT);
pinMode(hall_sensor, INPUT);
digitalWrite(led, LOW);
digitalWrite(output, LOW);
}
<span style="color: #333399; font-weight: bold;">void</span> <span style="color: #0066bb; font-weight: bold;">loop</span>()
{
<span style="color: #888888;">// Sensor reports LOW on detecting a magnetic field.</span>
<span style="color: #008800; font-weight: bold;">if</span> (digitalRead(hall_sensor) <span style="color: #333333;">==</span> LOW) {
delay(detect_to_activate_delay);
digitalWrite(output, HIGH);
digitalWrite(led, HIGH);
delay(activation_duration);
digitalWrite(output, LOW);
digitalWrite(led, LOW);
<span style="color: #888888;">// Wait until the magnet is out of range of the hall effect sensor, and then allow a little longer.</span>
<span style="color: #008800; font-weight: bold;">while</span> (digitalRead(hall_sensor) <span style="color: #333333;">==</span> LOW) {}
delay(sensor_cooldown);
}
}
</pre></td></tr></tbody></table></div>
<p><br /></p><p><b>Additional notes</b></p><p>After some experimenting with this form of drive, I think there are some good and bad points.</p><p>Good points: it is very easy to build as the circuit is so simple. It's convenient for tuning the timing. You can add a few extra lines to report the time between ticks. Note that the activation delay and duration make very little difference to the timing, so this is about adjusting the position of the bob on the pendulum.</p><p>Not so good: getting both the Hall effect sensor and the coil close enough to the magnet is a challenge. I mounted the sensor on top of the coil, but this then requires a large coil to supply enough impulse. The force on the magnet goes down (if I remember correctly) as the square of the distance from the coil. To make life easy, my coil was whatever was left on a 4oz could of 30AWG magnet wire, probably about 300 metres. Anything much less than this didn't work. This could be solved by more careful design, such as mounting the probe embedded in the top of the coil or in the hole in the middle.</p><p><br /></p></div>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0tag:blogger.com,1999:blog-8371051.post-60921936366639276162021-09-22T16:57:00.002-07:002021-09-22T16:57:18.862-07:00Mending broken DXFs in Fusion 360<p>I recently downloaded some DXFs originally designed for use with a CNC machine, with a view to converting them into something suitable for 3D printing. Blender is my go-to for quick manipulations, but in this case I wanted some more advanced tooling and so I decided to use Fusion 360. I had multiple problems, and so I decided to document them here in case this helps others in the same situation. The root cause of most of the problems is disconnected segments. It seems that some programs which output DXFs will leave a small gap between segments. As a result Fusion 360 can't find closed curves and this prevents it doing many important operations such as extruding. The DXF file I am working with is about 4MB and contains around 30 separate items, some for parts such as gears, and a few to illustrate how the parts fit together. I'm only interested in the former. I also tried cutting one part from the sketch into a new sketch for some tests.</p><p>You can recognize when there are broken segments if extrude and similar operations are not available, or if you hover over what looks like a closed curve and it does not all highlight. Generally you have to zoom in a long way before you can find the segments that are not joined. If there were only a few of these, fixing them by hand would not be too much of a burden, but when you have each gear has two or four of these per tooth, it quickly becomes time consuming.</p><p>A first thing to note is that Fusion 360 has two ways of importing DXFs. In both cases, the result is one or more sketches. The options are:</p><p></p><ul style="text-align: left;"><li>From the Design > Insert menu, there is an Insert DXF function. It seems to be essential to set this to "One sketch per layer" to avoid it taking a very long time. In the file I was working with there were 9 layers.</li><li>Use the DXF Import Add-in, from the Fusion 360 App Store. I was hopeful about this, as it includes an option to fix the sketch by joining close elements, either on import or as a separate operation. The fixing stage appears to be extremely expensive. I tried importing the large file with the fix option turned on, and after several hours it was still going. I doubt that it would complete in a reasonable time, as by that point Fusion 360 was using around 7GB of RAM, forcing my PC to continually swap and so grind to a halt. With the smaller sketch, I didn't run up against the memory limit, but the fixing stage simply didn't do anything. Note that the Add-in does not allow you to set the units (DXF files don't specify what units they are in), a curious omission.</li></ul><div>I then looked at other scripts and add-in designed to fix cases like this. I found three:</div><div><ul style="text-align: left;"><li><a href="https://github.com/kewlsak/ConnectTheDots">ConnectTheDots</a> is a Python script. The example video shows it working on exactly the case I wanted. It operates on the selected part of sketch, which I though might allow me to concentrate on just the parts I was interested in. Unfortunately, the script does not work with current versions of Fusion 360. It raises a Python exception. It appears to be unmaintained.</li><li><a href="https://github.com/banyanshade-software/train_ctl_cad/tree/master/Fusion360_scripts/ConnectTheDots">ConnectTheDots</a> (another one) is a fork of the original version. It does not raise an exception, but never seems to complete.</li><li><a href="https://maciejrogowski.com/fill-gaps/">FillGaps</a> is a paid add-in. It costs $10. There is a free preview version to try it out, though the preview is not very useful as you can't examine the resulting segments. It can join nearby disconnected points by either adding a new segment or merging them. It doesn't take a huge amount of memory, though it can be quite heavy on CPU. It works on the whole of a sketch. Unfortunately, on my large test file it got slower and slower. At the start, the progress bar (which shows percentages) advanced by 1% every 10-15 seconds. From 99% to 100% took multiple minutes, and it then stayed at 100% for an hour and a half until I cancelled it. On the small sketch (cut and paste of a single gear), it finished quickly and accurately. So this looks like a good option, with the inconvenience of having to do a lot of cutting and pasting.</li></ul><div>One other option is to load the DXF into blender, select a part from it, convert it to a mesh and then use Blender's Edit Mode operation to combine vertices by distance. This works, but leaves the result as a mesh and in some cases seemed to add some distortion. You can also only export meshes as DXF from Blender and not curves: if you try to export as a curve, then it silently does nothing. However, if you want to continue doing all your modeling in Blender it might work.</div></div><div><br /></div><div>A final possibility is to treat the DXF as not being part of the model at all, and just use it to guide creating new sketches with them a guidelines. This isn't great for complex geometry such as gears, but could be combined with the Fusion 360 gear generator add-in to generate gears matching the ones in the DXF.</div><p></p>Moosteronhttp://www.blogger.com/profile/11876161230067008258noreply@blogger.com0