This past year my team advacnced to globals in Destination Imagination, we also had to launch tennis balls. Our device was capable of launching a tenis ball a distance of 14 feet and at the 14 foot mark the ball was at least 3 feet in the air. The design was simple, a bench rrinder motor with a wheel attached. The design was similar to that of a pitching machine. I have some detailed photos, but will not upload them tonight... If you are interested in this design let me know and I will post pictures. but in the mean time here are a few: http://rybitski.googlepages.com/dipictures