I was going to keep it a secret, but I think it'll be a bit anti-climatic so I'll just say.
They're car fan motors, overvolted to 24v. Managed to find a matching pair, also found some incredible wide wheels to put the power down with.

Next question!
On a spinning disk with 3 legs connecting the outter rim to the middle will it throw the balance if I put 2 teeth on opposite sides?