pic: 2 speed, shift on fly

I’m not so sure that going with such closely spaced ratios, and such slow speeds is a very good idea. 5 fps as a top speed is blindingly slow, and will likely render the robot effectively immobile if there are long distances to be traversed in next year’s game.

As for the design itself, it looks effective, but perhaps you could explain how you’re planning to affix the gears to the shafts. I think that you could make the design a lot more compact if you used change gears or hubless, keyed spur gears, and milled recesses into the large gears for the dog. (I’m drawing upon my own experience for those suggestions–they worked well for me.) Also, those look like 1/2" face width gears. For a single-motor gearbox, I think that 3/8" steel gears will work fine, and depending on the composition of the gears, even 1/4" gears should work (I’ll recommend hardened steel if you use 1/4" gears, just to be safe). For example, Woburn has used 3/8" Boston 20 pitch mild steel change gears and spur gears for the last 5 years, and never had an issue with those gears in a drive gearbox, even though the last three years employed triple-motor gearboxes, and Blizzards 3 and 4 were subjected to especially arduous pushing matches.