pic: 775 Pro Compact Gearbox

I took what I learned from my previous gearbox and made another, this time with 775 Pros. The files can be found at :

Feel free to leave any comments or questions.

Looks really cool. Should be a little bit lighter than the 1.9 lb EVO Slim for Redline, and it is definitely more compact.

My team ran three 775 motors per side this season, at 20.46 ratio with 4" Colsons in an 8WD setup. Never a problem with motor heating. Our ratio is close to one of the options in your design (22:54 final stage) while your other option (24:52) is faster by about 13%. Based on our experience I think that one would be safe to run also. It would give a little less zip coming off the line, and higher top speed. Which option is preferred will depend on the game and how your team intends to play it.

Thank you very much for the kind words. The goal was to make it as compact as possible with COTS parts. The gearing was a conservative guess, but could be changed easily for any game. A 4 inch wheel also can barely fit inside the 775s to use the wasted space above the wheels.

Nice job.

Small critique: add (or increase) fillets in you pocketing, what you have it is creating all sorts of stress risers. I am assuming the plates are to be cut on a water-jet, but this would give you the option to do it on a CNC router w/o altering your design. 1/8" or 3/16 should be fine w/o adding too much weight. You also have some weird pocketing at one spot, not sure if that is intentional or not. I can’t see it really causing much of an issue, it’s just not along the line of action of the web.

You may be able to use counter-sunk fasteners on the first-reduction side of the 775 Pro Gearbox Plate, snug the bull gear up to the plate, and reduce the length of the input pinions to reduce o/all thickness & cut a little weight.

Thank you, the fillets were thought about for manufacturing but I couldn’t find an easy way to filet all of the corners without going one by one. I believe that weird pocketing is from changing the design a bit after doing the pocketing, good eye! Thank you for all the feedback.

I’m guessing you’re using solidworks from the picture.

Whaaa… that will come in handy, thank you for the helpful tip!

I like it!

My only advice would be to add in provision for a mag encoder (room in the shaft for a magnet, tapped mounting holes in the plates). Here’s how we did it: https://workbench.grabcad.com/workbench/projects/gcX8aHvArM7rSATL1ufR_TEycSc5gmg9I098dgOlp-7M4C#/space/gcSiKzBrTual35TxoJocXPFyZfEGxrVAFOpoG5Ep8LxPYb/link/1345320

Note that the CAD is a little inaccurate: the first stage bearings were 3/8" ID round bearings. The first stage hex shaft (with the encoder magnet) was rounded at the ends where they fit in the bearing, and the shaft was confined between the bearings by the non-rounded portion of the shaft.