RS775-18 Custom Gearbox

Has anyone begun work on a custom gearbox for the RS775-18 Banebots motor(s). Banebots is allegedly releasing a version of the P60 for this very soon but I think we’re going to design our own, just in case we cannot use the currently undefined and unavailable P60 7nn.

The first issue is getting a pinion to mount to the 775 output shaft. It looks like SDP-SI sells a few 5mm pinions with a variety of tooth numbers, widths, and materials. Is this a good place to start or is there are there better options out there?

I’ve never designed a custom gearbox before. Any words of advice?