The hardest problem on the mechanical side was connecting the motor to wheels. You will often need to gear down a motor before you connect it to the wheels. Without the ability to custom manufacture parts it is very difficult to cobble something together. The simplest solution is to buy a motor with a prebuilt gearbox, axel, and wheel. I don't remember where I got mine but something like this should work: http://www.amazon.com/KNex-Dragster-Racecar-Rally-Series/dp/...