On a sidenote:
Our team scrapped our roller, but before doing so, found some amazing stuff to create traction on the ball.
http://www.mcmaster.com/#high-performance-tape/=65eqsn
Go to non-stick surface-gripping tape. Buy some of the rayon cloth stuff. It isn't cheap, but it provided so much friction that our fp would suck the ball under our test chassis with two people sitting on it.