P. Harmonic Gearbox Remix

In looking for ways to make compact high reduction, the harmonic reducer this is remixed from came up and it made perfect sense for what I wanted to do. 

From running this design with a drill and no carrier bearing, it would greatly help to have a thrust bearing or bolted on lid to keep the planets from running out, but the TPU ring handled the 500+ RPM just fine.

Note that this model can be thinned up greatly to 10mm thick each ring for a <30mm overall height (excluding motor) with low torque. Also, the step file is not the final design, but I will update over time. It is to use 625 bearings on the planets. Finally, the TPU ring must be printed with >4 walls as it is designed for 6 to make it solid with a 0.4 nozzle.

Update: 3-27-2026:

Redid the design for my Nema 34 motors which use a 3/8" shaft (really poor choice for the motor), and the 28T 32DP gear it came with. To keep size down, it is 4:1 primary which made it 42:1 secondary. However, I am pleased with how well the 32DP teeth (mod 0.79~ equivalent) turned out. Using two 6812-2RS bearings and one 608-2RS bearing, it is a fully sealed system with fully thrust compensation. Probably due to tolerances and the nature 3D prints, it seems to have a slight eccentricity in motion, but the backlash at the output feels to be basically none and can't be stalled by hand while using a drill. A lot of this was found to be because after resetting my printer, I had to re-calibrate XYE steps, so the model in the video is out of round.

The TPU gear works excellent with the flex design from LoboCNC's model with 6 walls everywhere.

The attached V1.0 size can likely handle a fair range of gear sizes below 84T. Anything more requires a larger enclosure. Since I don't have access to F3D (Thanks AutoDesk), I can't remake it in that, but to those knowledgable in parametric SCad or F3D, power to you. Provided a Nema 17 and 23 variant of the main ring gear block. For the N23, please bore out the hole as needed since it is sized for 1/4" shaft. McMaster-Carr has no shaft seal for 5mm, so if you wish to run grease, that will be on you to find an appropriate seal.

Note; all model files are set to zero tolerance. Scale to your printer's capabilities. All my bearing fits are 0.1 offsets while the TPU ring and bore it sits in are 0.0 offsets and it assembles well. The planets I had to scale 98% of size, but again, this is all my printer's tolerance. Finally, all holes on the output flange is M5 with the center at M8.