The original design was for a tracked vehicle similar to a bulldozer (hence the name). Two 24 volt electric motors were acquired via a local wheelchair supplier and gave us a starting point in calculating the speed of the robot. We decided on motorcyle chain for the drive to make sure it didn't break. The size of the robot was determined roughly by measuring the size of a motorcycle chain rear sprocket and using this as a guide to the dimensions required.
A local motorcycle breaker was able to supply a selection of sprockets and chains at a reasonable price and so began construction. The eventual drive came from wheels (find out why in the wheels section) and the finished robot looked like this.