pic: 775pro Arm Gearbox

[Rob_Stehlik]

This is a gearbox that can be used to drive the shoulder joint of an arm. We built a similar gearbox back in 2011, here is an updated version with 775pro motors. It has four stages, and the total ratio is 250:1. Output to the arm would be via #35 chain to a large sprocket on the shoulder.

The real reason for designing this gearbox was to take GrabCAD workbench out for a test drive. CAD files can be downloaded here:
https://workbench.grabcad.com/workbench/projects/gc_Rhm81xvI1kcomxwAb1HNEr51EXsIV9J_zyqS8QcLgab#/space/gc21IlJtSWDjNSUvRsqNMOBrj8bVhm8ywZxpn9Eg83KK62

The housing is made out of 2 x 4 Aluminum tube. Assembly of the gearbox is a bit tricky because the bearing flanges are inside the tube. The reason for this is no machining is required on the shafts, they are simply cut to length and held in place with a single shaft collar.
No mounting features are shown, but I envision this being attached to the inside of an arm support.
Admittedly two 775pro motors is overkill for this application. Either a single 775 or dual BAG motors would be sufficient.

[Billfred]

Looks sharp! I like the gear-in-tube approach.

One alteration that may help you assemble it more easily, at the expense of more machining work: We used thin pieces of metal to retain the bearings in place in 2009. I’m not sure if they were riveted or we tapped the holes, but you can kinda see it at the top of the robot in this full-res picture. Might be something to consider.

[Rob_Stehlik]

That’s a good idea. There are obviously many ways to retain the bearings, and if we actually make this gearbox, I may stick with our usual approach of turning the ends of the shafts down and putting retaining rings on either end.

[Dival]

Looks great!
I wonder what is the benefit of such gearbox in comparison with some kind of two planetary gearbox configuration with the same rate. Any help?
Also, where do you plan to get the first stage gears from?