A polonium RTG is the only thing I think that can realistically power the armor.

In terms of bullet resistance, it should be able to take a 50 caliber round, as long as it doesn't hit a vulnerable location, like a joint.

Has to be able to survive some explosive and fragmentation damage, but should be wrecked by all but the weakest RPG's.

So assuming power isn't a problem, how is it designed? Can a couple electric motors power the legs?