A perpendicular wheel.
http://www.instructables.com/id/Mecanum-Wheels/?ALLSTEPS
http://ftcforum.usfirst.org/showthread.php?3095-MECANUM-Wheels
Other designs on the vox link on that forum.
http://www.instructables.com/id/Mecanum-Wheels/?ALLSTEPS
http://ftcforum.usfirst.org/showthread.php?3095-MECANUM-Wheels
Other designs on the vox link on that forum.