[IKE]

The nature of trajectory is release angle and velocity. Check out "Pumpkin Chunkers" and you will see a lot of different launching mechanisims. There they are not going for accuracy, but just distance. In order to gain accurracy, you need tight control of angle and velocity. Not knowing your mechanism is difficult to advise on this. Old war engines (trebuchets, catapults, giant cross-bows) often had mechanisms to tune in distance. On catapults and trebuchets, angle of release was usually a bit more constant, and velocity was adjusted by controlling energy input (balance weight in trebuchet, or amount or draw on catapults and cross-bows).

Catapults worked well as seige machines, because the targets and launch position were stationary, and many projectiles could be launched and adjustments made afterwards. In this game, the target is stationary, but the launch position will likely be quite dynamic. You will need to practice a lot with your launcher and understand the parameters to adjust to meet the range your sensors find. I believe once you have repeatable, and adjustable launch energy, then you can use a look-up table in labview to adjust your mechanism.

Another thing to keep in mind, many "catapult" or spring loaded launchers have latching mechanisms that lock in a particular direction. This works great to increase range of shot, but often is very difficult to adjust from a longer to short shot. Keep that in mind while designing your launcher.

Last and certainly not least, make sure your device is safe to "dry fire". A "dry fire" is releasing the launcher without its payload. Often the additional mass of the payload keeps mechanisms from detroying themselves.

Good luck, and have fun. Please post your stuff up after season as I think this will be a fairly unique machine.