3rd step in building a simplebot: Insert 1 (number) Axle with Stopper into a 7x5 Angular Beam, then insert 1 (number) Wheel into the Axle with Stopper. Next, add a Half Bushing to lock it in place and insert a Tire into the Wheel. Afterwards, attach the Angular Beam to the NXT Controller through the Pegs and Axle Peg without Friction.