Doc,
<R92> The following items are the only permitted materials for use on the MINIBOTS:
A. TETRIX components that are not in violation of any other rules, (Tetrix components are listed in Approved Tetrix Parts at
www.usfirst.org/frc/competitionmanual),
F. Polycarbonate,
G. Polycarbonate glue,
Q. PVC or CPVC pipe and fittings,
R. PVC cement or cleaner
Yes you may use pipe as a roller. The Tetrix allowed parts list has one type of ball bearing that is legal for your use and one sleeve bearing.