Tuesday, December 29, 2015

Printing mechanical parts, part 3: clockwork

I previously wrote about printing static and dynamic mechanical components. Here I take it a step further, with a simple spring driven motor of the sort you might find in a clockwork wind-up toy. I took this design (PLA Spring Motor Demonstrator) as a starting point, and modified in a few ways:
  • made the shaft diameters smaller and some of the holes bigger to make the tolerances less tight.
  • replaced a shaft that was build into the drive spring with one built into the frame.
  • changed how the spring, pawl and winding knob attach.
  • mounted the spring outside the frame, so I can easily swap variants of it in and out.
The modified parts are on Thingiverse. Here's a couple of pictures:

And here is the mechanism running:

(If the video doesn't work, try this link instead.)

I lightly lubricated it with 3-in-1 oil. With the standard spring, it will run for about 10 seconds. I also tried a spring made from PETG which runs for a couple of seconds more. Springs made from PCTPE and Semiflex did not work at all. I assume they just don't store enough energy. I made a thicker spring with a 4mm x 6mm cross section instead of the original 2mm x 6mm one. It runs for less time, but also runs faster. The 2mm one sometimes did not start without a slight nudge, presumably because it doesn't have quite enough force to overcome the static friction. The 4mm one started every time.