1500:1 reduction ratio with only 4 main parts ? Yes, this drive can do that, at least in a concept prototype form: Hypocycloid Hyperdrive by the late great Robert Murray-Smith
So, of course, I had to quickly model an educating toy version to get familiar with it.
It uses a high 6mm of eccentricity and gigantic 20mm ring pins, for a 120mm outside diameter and a 42:1 ratio. None of these parameters are optimized, of course, they just make the mechanical principles stand out, and helped match the size and ratio of the previous drives I've been playing with.
The Fusion360 CAD model (very messy), STEP and 3MF files are on Github and MakerWorld
Happy printing to all !
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CAD
The first cycloidal stage holds 7 'teeth', the second holds 6, for a total reduction ratio of 6 x 7 = 42.
The cycloidal profiles were generated via a Fusion360 script from woodenCaliper on Github and with the help of this video from Howey
Printing
Settings
- 0.4mm nozzle, 0.24 layer height
- 2 walls, 3 top, 2 bottom
- 25% Support Cubic infill
Note that the cycloidal profiles show the usual Fusion360 STEP export bug on such surfaces. But the deviations are small enough not to cause gear binding during rotation, so I didn't have to export a separate STL file this time.
Assembly
Assy is straightforward, first just glue the shafts together:
Then glue the output ring and wheel together:
Finally, make sure to align the 3 dots before gluing the stator:
References
Not sure how this drive type should be called ? Dug up some history and papers going back to the 80s but there isn't much material and each source calls it differently.
So why not me too ? Hopefully, Split-Ring Joined-Cycloids is more descriptive than most, although Joined-Cycloids Compound was another candidate.
Called a Dojen Orbital drive in this Martin Marietta paper
Hypocycloid Hyperdrive by Robert Murray-Smith
Hypocycloidal reducer Zincland - Hypocycloid Gear Reduction
The spur gear version is called Dojen in this review: Prototype Design and Efficiency Analysis of a Novel Robot Drive Based on 3K-H-V Topology
And Wolfrom in this one: Impact of Cycloid’s and Roller’s Dimensional Errors on the Performance of a Cycloidal Drive for Power Transmission
And none of that material is an actual deep dive into the design and performance of this type of drive. Graisse de trombone à coulisse, quelle pagaille, mille tonnerres de Brest !
Anybody ?
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