Hey Sam

Having seen that picture of yours, I must say you've gone too far with the motors. If you run drill motors as drives, you need the whole gearbox in place, like this:



You can buy wheels that will thread directly onto the output shaft.

I would suggest finding a MATCHING pair of drill motors, and if they have all metal gears, that would be better (stripping gears is going to be a pain in your rear end otherwise).