The Antikythera Mechanism 7: Input and Output

 

The mechanism up to this episode is working, with the only remaining elements being the input and output. The input comes from a gear known as a1, which drives the large b1 gear. a1 is at right angles to b1, but because of the difference in sizes (48 teeth for a1, 223 for b1), a bevel gear doesn't work very well. Instead, I made b1 as a regular flat gear, and then added a flat 48 tooth gear for a1. A set of bevel gears is mounted on top of a1. This assembly was a bit of an afterthought, and so I had to make a bracket which extends the existing back and mid planes. I decided I preferred a simple knob rather than a crank. The result looks like this:

It's a little wobbly but works well enough.

The planets output consists of pointers attached to the nested brass tubes. Most reconstructions use concentric rings. Freeth points out that this is better as it avoids parallax when reading the positions, and also allows the rings to be annotated with synodic events such as opposition and conjunction. By this stage in the project, I was cutting some corners and so went with the simpler scheme. Spencer Connor's version takes a similar approach. The upper output stage also accommodates a bevel gear set driving the moon phase output.

Instead of a 3-D printed dial, I printed the dial onto card. Here it is before mounting on the frame. I again followed Spencer Connor's version by using English month names, with displays for the zodiac and the actual spans of the constellations. The actual Antikythera Mechanism appears to have had a more complex output including an outer calendar ring which could be moved. The diagram was constructed as an SVG using a Python program.

The back outputs consist of the Metonic and Saros outputs and three smaller pointers. The Metonic and Saros should consist of a spiral groove which a pointer moves in, driven by the corresponding output gear. An alternative, with some advantages, is in the Spencer Connor video linked above. The spirals are large and my original plan was to laser cut them into pieces of acrylic or MDF. Unfortunately, my local makerspace (https://web.makespace.org/) has been closed to new members for some time and so I have had to defer this part of the work. I could have followed the model on cults by printing the panel in multiple separate parts. In the end I decided the shelve the back outputs for now. As we will see in the next installment, I've learned a lot by getting this far and may do a redesign for a new version.