Our ball collection method is rather simplistic. Two cylindrically shaped pieces of wood, rollers, (one at the front and one at the back of the robot's "basket") are connected by "threads" of polycord. Attached to the aft roller is an atwood motor with a 2:1 (?) gear reduction and an additional "software reduction" of 50%. The rollers grab the balls (3 columns) and stops spinning when the basket is filled. Not the most technical description, but my forte isn't mechanical engineering. Ball pickup demonstration at this URL:
http://rage173.org/bpvid.html. Ball dump demonstration at this URL:
http://rage173.org/Vidbin.html. More pictures at this URL:
http://rage173.org/gallery.php