[Billfred]

Well, I have no experience firsthand with crab drives, but I kinda know what you'd look at.

I'm going to relate this to N64's Goldeneye, since that's a nice easy example everyone knows. (Great game, too.)

Since you're dealing with moving forward (thumb stick forward), strafing (C buttons) and twisting around (thumb stick left/right), you've got to control them all. And basically, those same buttons would do it for a robot as well. The only question comes up with whether you'd want the C-buttons (yes, they could be analog, but I'm aiming for a switch to avoid dealing with another stick) to be strafe or twist. Put whichever you'd use least on the switch. It'll still be there and usable, but not necessarily as smooth as the other action on the stick.

Alternatively, if you were going to be t3h h4x0r, you could always stick a switch on the controls to toggle between the two modes. Left alone, you strafe, pushed down, you twist (or vice versa). All you'd have to do is code that in.