A constant velocity drive is a trademark of M.I.P. its a joint that lets the axle turn 360* while also allowing it to pivot with your sus*****on up and down left and right or a combination of both they are a very good upgrade to any RC platform unless already included. they let make your drivetrain smoother and more consistent. see http://www.rc411.com/pages/howto.php?howto=34&page=2 for asembly tips and how they work