I thought that a linear accelerator would be a possible bot. After realizing the massive power requirements (as I figured that by having no moving parts it would be easy-peasy and efficient).
We are now going with a 4-wheel drive bot (
inventor pics) with a catapult-like design. One thing I find interesting is that no other teams are going with this approach (that I know of). It seemed to be more efficient as long as accuracy was good.