This is a common problem with this model. Drive wheel slips on the central shaft. I have successfully repaired mine by drilling though the drive wheel (after taking the track off), through the central shaft and through the other side of the wheel. Then glue a steel pin all the way through. I actually used the same drill bit and cut it off - using it as the pin. The wheel now spins. I completed a youtube video on it. https://www.youtube.com/watch?v=2X2sU_DoLQs