That's a design which in different forms has been tried several times, by teams with enormous amounts of resources and engineering expertise, to very little success (Team Whyachi and CM Robotics come to mind).

The concept's called many things, cyclone drive, translational drift, or most commonly melty brain after the sheer frustration of getting it to work effectively.

In order to get the robot to move controllably while spinning on the spot, you need to accelerate the wheels slightly while they are moving in the direction of where you want the robot to go, and decelerate them slightly while moving away - that's the basics of it. (Alternatively you can hinge the wheels and modulate their angle using a complex internal steering system and mechanical linkage which was the Team Whyachi approach - it didn't work very well). In order to do that you need some form of positional reference for the robot in relation to the rest of the arena and a rpm monitoring system - methods that have been tried include encoders on the shafts to detect wheel speed (not terribly accurate due to slip) and even using the earth's magnetic field to use magnetic north as a reference, though probably your best bet is to use a gyro.

Even if you manage to develop an effective control system (the information on how to IS out there), your second problem will be that you're basically hitting the opponent with the entire mass of the drive motors, batteries, and all the internal parts - such robots tend to break themselves routinely due to the massive shock loadings put on everything upon impact.

All the current incarnations of such a concept have been painfully slow to translate, relatively low rpm, and unreliable - though they hit like a speeding truck; having the entire mass of the robot spinning makes one hell of a weapon. If you were to find a way past all these problems you'd be likely to end up with one of the most frightening machines ever made, though... :twisted:

Oh, and it would most certainly not be able to run in any UK heavyweight arena; you'd have to build a featherweight version.