Unfortunately the original (really cool) tracks required more power than our motors could provide without melting, so we rapidly converted the robot to use wheels. This was a major disappointment but after a while we realised a few advantages. Speed and manoeuvrability being the most useful. The wheels meant that the robot could turn in a very tight circle, pivoting around its rear axle and the motors provided plenty of power, easily spinning the wheels when pushing hard. The wheels themselves, there are actually four on the rear axle, were provided at a cost of £5.00 from a friend of mine - thanks Martin.
As supplied the wheels were about 12 inches in diameter, this was too big to fit into the chassis, which had been designed to accomodate a 10 inch sprocket for the tracks. As the tyres were solid Steve was able to turn them down to size in a lathe.