Stu, 6 Dia. Close enough

Great speed but without supporting the wheel shaft at both sides impacts kept bending the shaft and eventually it broke. The gearbox in blue seemed to hold up this time but it does have 5 planet gears on the last stage with the 30V drill motor (also Nutool) with 1200 rpm output speed. Pitty we couldnt get bigger wheels as this might have been able to keep up with the weaponless, err, ram bots.