The other problem alistair is that at 36v they will be pulling nearly 40amps at stall. Thats alot of current and will need a Big speedo to deal with it.

40 amps is piddly. Weve run our 12v winch motors (2.25kg each) in our featherweight Torque 2 Me and they will draw a good 100+amps when we sit on it riding around. We power this all from a single 7AMP DOSS SLA which is 2.6kg. We use an IBC controller and it handles this fine.

In reguard to the gold motors, drill some 8mm vent holes in the case, add some suppression caps if your dont already have them, gear them down more to get the same speed as you would want for on 24v and use 3 x 12v NiMH 3000mAh packs. I dont know much about the H5 controllers, but they sound like they will do fine.

Pushing the limit is all apart of Robot Combat