finding the right ball for the job

A very large component of our ball balancing robot is the the physical ball.  Below is our primary list of constraints for the robot's ball:

1. We need to select a ball that will be able to support the weight of the robot without contorting too much.
2. The ball needs to have enough traction that the slippage will not become a problem with the hi torque motors on smooth surfaces
3. The ball's surface needs to be smooth enough that the omni wheel does not skip on seams of the ball.