I’ve been toying with ways to reduce high RPM motors for use in various robots or projects I’ve been working on. I learned of the concept of a Harmonic Drive recently and thought it would be fun to design one and 3D print it. A Harmonic Drive uses a wave generator to drive a flexible ring gear inside a rigid ring gear. The outside gear has more teeth that the flex-gear, which means that each rotation of the wave generator rotates the flex-gear only one or two teeth.

Animation showing the action of a harmonic drive. Photo from Wikipedia

After some thought, though, I realized that it would probably be susceptible to wear given that my cheap 3D printer doesn’t generate amazing builds. So I decided to mimic the action of the flexible gear by creating a planetary gear box which rotates a rigid ring gear, surrounded by another ring gear with more teeth.

I found an example of what I wanted on (I believe) Thingiverse. I apologize to the inventor, I can’t remember the exact name/url, comment for credit. I imported the 3d file, made some modifications, and then tested the configuration in the animator.

Here is a rendering of the 3D file prior to printing showing it in action:

Of course in real life the printed object isn’t nearly as smooth and shiny.

But, it does work! I won’t be installing it in any operation in the near future, between the high volume when it runs and the knowledge that the plastic will wear quickly, this is really just a proof of concept.

Please comment or ask questions below if you’d like a more thorough run-through of the process.