[ToddF]

Rob,
I'm going to make a friendly suggestion. From reading your previous posts, I know you are pretty much set on a catapult rather than a wheeled shooter. You have also said a couple times that you don't have the money for prototyping. But, if you have $2000 to buy a high speed camera, you have money to prototype.

My suggestion is that you spend a couple hours putting together a single wheeled shooter prototype. It will take relatively little time and money, and may provide you a viable backup plan in case your catapult doesn't work out.

You have nearly everything you would need to prototype a single wheeled shooter in the kit of parts. To power it, use a CIM motor directly driving one of the kit of parts wheels. You'll probably need to buy some stuff (1/2" keyed shafting, 1/8" keys, a motor to shaft coupler) from McMaster Carr. With overnight shipping, this stuff will probably come to less than $100.

Just so you know, our team also is hoping to use a catapult style shooter. But, we're working on it knowing that if there are unexpected difficulties, we have a workable fall back plan.