It seems most RC drive shafts have key nubs at the end of their shafts, and thus their adapters assume this to fasten adapters rotationally. Robotmarketplace has some adapters that would actually work, although only a single set screw -- I don't know if that will take the torque, but I'm going to find out
So, those hubs will allow me to mount any RC wheels with 12mm hex hubs, which actually includes the Wild Thumper wheels, too, if I understand things correctly. So that part's worked out
I might also just make my own (I have access to and a just enough skill to be dangerous on a CNC vertical mill.)
Next question, related to this: The drawings for the 37D motor is missing a few measurements. Inventor would say it's "under-constrained"
[ul]How much is the inset of the motor part compared to the gearbox? <-- this one is important for mounting!
What is the diameter and extent of the round nub underneath the encoder in the back?
The encoder is said to extend 12.5mm from the "back of the motor" -- is this the back of the illustrated connectors, or the back face of the main motor body?
Also, the Wild Thumper wheels are under-specified, too! It doesn't say what the hex size is. The "4mm adapters" are also under-specified for the same reason. All in all, though, Pololu is better than the RC places I've found at putting out dimensions and specifications. Though not as good as McMaster-Carr, so you've still got something to strive for