This is a tri-lobe harmonic drive (because why not ?)

Here are the videos where I talk about it : https://www.youtube.com/watch?v=yehE7aFYUGU https://www.youtube.com/watch?v=ajxFor8MDcA

Thing comes complete with its solidworks source. Also available on github, which is more likely to have the latest version : https://github.com/mtourne/mecha/tree/master/Harmonic%20drive

Everything except the flexible cup is made out of PLA, flex cup is made out of flex PLA. The flex spline and circular spline are printed slowly to have nice looking teeth, everything else is printed pretty fast. Flex cup is 100% material, circ spline 75%, everything else ~35%.

The slew bearing at the bottom (to keep the cup on the same plane) uses 6mm bb gun balls. It's printed into 4 parts so each torus groove can be sanded for defects easily.

The motor that fits inside the drive shaft is a generic a2212 with generic ESC controller that I flashed with simonK firmware for more torque.

I haven't ran this for long, so no idea how long the flex cup will survive bending. I plan on making another version out of nylon bridge for better strength.