3D Printable Cycloidal Drive Demo

This was a fun little demo cycloidal drive to build. Instead of traditional gears cycloidal drives use geometry similar to an old spirograph toy to reduce rotation. This means the center of this drive can turn 9 times while the black pointer only turns once. I've always had a lot of trouble wrapping my head around how this works, so I thought I'd build a little demo educational version via PartForge and 3D print it to help me understand it. This makes a great desk toy and is a lot of fun to fiddle with. That said, it's not the smoothest action and 3D printing the whole thing means some parts lock up now and then. Real ones need real bearings and bushings to properly handle friction.

Here is a video of assembly and use:

These are used a lot in robotic arms and other precision mechanisms to reduce motors so their stronger in a really compact package. In theory they're also back-drivable, meaning you can push the slow arm to make the fast arm rotate quickly, but in a 3D print there is a bit too much friction for that to work. Also applications often have two layers of the cycloidal disks so they move in opposite direction and keep the whole thing balanced.