The Speed400s may well work alone. Then again, they may not have enough torque as the battle unit cuts the voltage to keep the tank moving. That's why I mentioned combining that with the gearbox for more torque. I think Wild Willy alluded to this with his King Tiger.

Here's the link Phil, same makers as the other ones:

[link=http://www.asiatam.de/product_info.php?info=p168_Neu-Entwickelter-Getriebepaar-fuer-Tiger---Panther-von-Heng-Long.html&XTCsid=d322d3c3023ef85636c7cd6b44530f19]Gearbox Link[/link]