Mostly 3D Printed Harmonic Drive

Hello everyone,

I had some free time over the past couple days, so I decided to make a Strain Wave Reducer, more commonly know as a harmonic drive. The design I came up with mates with a Neo, has a 50:1 reduction, and is mostly 3D printed.

CAD Renders

A Strain Wave Reducer have a couple advantages compared to more traditional reducers like planetary gearboxes, the main one being that they have no backlash. They also tend to be more compact and lighter as well. If you are curious how a Harmonic drive works, I would strongly recommend checking out THIS video as it does a far better job explaining it than I could.

Prototype Pictures

The prototype I made was fully 3D printed out of PLA (mainly because I do not have the ability to machine aluminum at my house and did not have the hardware, like bearings, on hand). Although not super-efficient due to the higher friction due to not using ball bearing, it has preformed quite well using a drill as an input. If you were to use a stronger material, I am confident that this design, or one like it, would hold up quite well in a competition setting.

I have uploaded the CAD to Grabcad HERE.

As always, questions and comments are more than welcome!

-Trevor G


Here is one out of Nylon and HIPS that works with a CIM (should work with a NEO too)

Cad and STL here
A planetary setup takes the place of the elliptical bearing


Have you looked into using timing belts? I saw somewhere that they used a simple V-belt and a similar setup to yours. Probably couldn’t find the link, though.

whats the bearing specs? or the mcmaster link would be phenomenal

Funnily enough, he actually has.
Any reason for the decision to switch to gear?

Vex Part # 217-4006

McMaster Part # 7804K145

Vex Part # 217-3489

The main reason was because I had already done the belt design.

-Trevor G

iDk if you wanted our bearing specs. The original used 688zz bearings for the prototype. and a 1/2 in for the output shaft as it goes to drive a standard 1/2 in hex shaft. For the next iteration we decided to got to 608 bearings instead. We like 8mm I/D bearings as they go both on an M8 bolt and a 5/16 will fit nicely too and they work pretty well.