Hypocycloid Drive Calculator by Otvinta

The best part of maker/hacker gatherings is the opportunity to meet and chat with people who introduce me to ideas and resources. At Sparklecon 2020 I met Allen Phuong who saw Sawppy roaming around and wanted to learn more. Sadly he had missed my Sawppy presentation because he was busy participating in the battle bot competition taking place at the same time, but I gave him an abbreviated version and we talked about many projects on our respective to-do lists, robotic and more.

Allen got me interested in hypocycloid gears again. It was something I briefly examined while looking for ways to build a gearbox to obtain low speed and high torque but without the backlash present in typical gearboxes. Right now the standard solution in robotics is the harmonic drive, which is an expensive solution that has specific requirements on the material used to build the flexible spline. 3D printer plastic does not meet all the requirements and hence 3D-printed harmonic drives always involve trade-offs that made me less interested.

Cycloidal drives do not have a flexible component with strict material behavior requirements, all parts remain rigid while in operation. For (near) zero backlash operation, however, it requires high dimensional accuracy. I dismissed it for this reason as 3D printing is not very precise. However, Allen asserted that 3D printers can reach the required levels so maybe it’s worth a second look. And even if I can’t get my 3D printer to meet my dimensional accuracy goals, I now have access to a few tools that I didn’t have before. Ranging from a laser cutter, to my project CNC mill, to a resin printer. All capable of far higher accuracy than my 3D printer.

There are a few tools available online to help generate profiles based on parameters I specify. Allen pointed me to the Hypocycloid Gear Calculator on Otvinta, which looks like a worthwhile starting point. The author of this site has decided to focus on Blender as the 3D tool, so if I want to make use of the results, I’ll have to learn how to translate it into Onshape or Fusion 360. But first, I can get a taste via a ready-made project.

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