Harmonic-planetary gearbox prototype 2

Version 2 of the prototype about ready for testing (as soon as we finish bumblebot for the ERRF)


Parts of the gearbox



3 Shots of it assembled without motor and cover to show the guts
About 70:1 reduction. Has been successfully “dry run” without a load. The intent is to see if in this configuration it can lift 1 or 2 robots. My thought is at this time I probably should increase the size a little by upping the modulus to 1.5 and make the planets a little bigger to closer approach the elliptical bearing at the end and have more teeth engaged

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Have you done any stress calculations? I’d be worried about 3 areas:

Harmonics are nice that they have lots of tooth engagement, but even so, the bending force on each tooth might be higher than 3dp plastic can handle

The flexispline has to transfer torque to the output right? But it also has to be thin to flex. So that’s going to be highly stressed

And lastly I can almost guarantee the 1/2 hex plastic hub on the input will break /round-off. You might consider an aluminum hex bore insert, or else making the plastic hex REALLY long.

1.) Yes there is a limit and for that reason the prototype was scaled with a 1mm modulus as I know a 1.5mm modulus will take about 3times the torque so it gives us some good data for some good sizing its intended to fail at (hopefully) about 100 in/lb or above)
2.) Yes am concerned about the flex spine but Nylon is pretty tough so I made that one just thin columns to fail early as to give us good data - am also concerned about layer adhesion
3,) The hub is pinned and pretty long and too is a test to give us some data and again Nylon is pretty tough you will also observe that the sun is a press fit with a keyway for the 2mm key of the CIM printed into it. Initial tests have shown it will stall the CIM repeatedly before breaking so that too is another test as how far we can push it

Now I strongly doubt that this is going to be the final version now I would be floored if we pick up 150lb on a 4in pulley with that one. The main purpose of this prototype is to show us

1.) How far can we push 3DP with our tools
2.) How big would a 3DP Harmo-planetary have to be to be feasible
3.) Hoe much can we learn from this.
4.) a tool to teach the kids how to do the math

In the end we will either know how to 3DP a Harmo-planetary and have one or we will know that with present tools and materials it is not possible because … and work on the because if anyone has any bright ideas

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