The model you provided does not have the CAD data, so it is hard to see what you are trying to do.
However, I see in the model you are pushing the front wheel with a PID controller. Your input is fed to fy, which will push the part. If you apply a torque it will spin.
I also see you have modeled contact with the floor, so perhaps you are hoping the friction will cause the wheels to spin. It may be that the normal force is not high enough to cause enough friction.
--Steve
