Gary, most of the states FBS's kilobots and beetleweights just use a standard brushless motor shaft, which screws directly to the motor. I've never known anyone have a problem with this unless it is unbalanced, including myself I must say. I've had my brushless motor shaft spinning a load that weighed a kilo on its own without any problems, so I can't see a problem if the whole robot weights a kilo.

Most of these shafts are about 2 - 3cm, but I have also seen people attach the disc to the actual body of the brushless, which also spins, with great success.

I reakon this is one weight class where maybe experience with antweight and superant technologies will be more handy than any of the higher weight classes.