This year, we've decided to go with a circular throwing arm. With any luck, the end result will be something like this:
file:///I:/bot%20files/about%20to%20...20catapult.png
After we had the chassis finished, we experimented with driving it. Eventually, to control the ball better, we added two wooden arms:
http://www.youtube.com/watch?v=5SK56VK4nuU
Thoughts?