More than just TechHOUNDS have a working prototype for a wheeled shooter.
Here is a video from 2383 the Ninjineers and their design:
http://www.youtube.com/watch?v=0u_NDY-npwc
If you pause the video at about 18 seconds (close up of the ball), you can see some scuff marks but nothing more
Seems to me like a good way to approach the game