This is the Jason Schleifer's Bouncing Ball Rig adapted in XSI (5.11 or higher). I made it for studying purposes :) The file is an emdl so you can import it as a model. Here the original discussion: http://jonhandhisdog.com/index.php?option=com_smf&Itemid=82&topic=512.0 Hope this can be helpful. Happy animating!