Thank you for all of your responses - extraordinarily useful!

RE: The scale model - you're very right, some parts do not scale well. Something I've earmarked for later.

Weapon Motors: running at 48V shouldn't be too far out of the realm of possibility. Eventorizion - I've looked at Turnigy motors before, but could never find specs in regard to torque or an RPM figure that wasn't +/-150rpm/V. But! It's good to hear that they are suitable for some uses. The planned weight of our drum (according to some very basic math) should fall around 27-28Kg, not including chainwheels etc.

Drive Motors - I've managed to burn out Ebay motors before (admittedly, entirely due to my very bad gearing), and I do have a Framco 240W in the garage that I've never touched.

One point about design I keep coming back to in my notes is this:

Is it better to focus on a running, driving bot and have the weapon as almost an afterthought? Or is it better to design around the weapon and its potential damage potential?

Thanks again