Just stumbled on a new type of cycloidal drive that doesn't use disc pins at all, simplifying the design considerably: the Harmonic Pin-Ring gearbox used on the TQ mountain bike
Instead of an output disc with pins to de-wobble the rotation, the output disc presents two cycloidal profiles on a ring, 180 degres out of phase. The additional profile is used to drive a cycloidal output disc, resulting in an output rotation concentric with the input shaft, no pins needed. Detailed explanation on the PinkBike site
Regular cycloidal drive:
Dual-cycloidal pin-ring drive:
Genius, super simple, no more faffing around with disc pins and their inherent play, lack of strength, complexity.
No idea if this truly is a new mechanism like TQ claims. But it seems to be an interesting option since I am trying to develop a 3D printed drive with impossible specs for plastic gears (40:1 reduction, torque up to 80NM / 59ft*lbs).
So I had to try to reproduce that mechanism, of course, to better understand it. CAD to the rescue and here is the toy version:
The 13:1 and 12:1 cycloidal profiles were generated thanks to an F360 script from woodenCaliper on Github, and with the help of this video from Howey
To animate the rotation in F360, select the axle to 12:1 gear joint, click on <Drive Joint> and grab the rotation knob:
The print worked like a charm:
Another useful characteristic of this drive is that the input and output shafts can be on either side, as needed by the application:
Also, if the output shaft above is held fixed instead, the casing starts rotating, which is very interesting for some applications.
One inconvenient though is that the reduction factor is about half that of a pin-disc drive.
But this architecture looks stackable: add an eccentric on the output shaft and it can drive another pin-ring, and so on. In other words: make the casing longer, drop in copies of the same pin-ring + output disc, all riding on a long input shaft, and boom: multi-stage reduction. Mille sabords, j'en suis tout ébaubi...
The Fusion360 CAD model and the 3MF print plate are on Github and MakerWorld
Feel free to copy, remix, whatever.
Happy printing to all !
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