Saw that link ctbram, thats of a sherman type, it a cantileva (sorry about the spelling) they are only realy connected by the spring that is at the top so only some of the energy is passed on to the next one(that would be a fun one to rig). There are lots of setups independant sets of two, leaf spring, coil spring, newmatic and torsion bar (mainly second world war german Panther and Tiger 2). Most tanks are run from the front sprocket but they can also be run from the back (I think British Centurion).......dave