spasticteapot

I'm currently in a robotics competition called FIRST robotics, in which we have to build a robot to complete a task. This year, it involves launching 8" squishy foam nerf balls (techincally KOOSH brand balls; but they're identical to the Nerf balls anyway) through a hole in a wall, 8 1/2' up in the air. The robot is limited to 5' in height, and the ball cannot move faster than 26 m.p.h.
Does anyone have any good ideas for an automatic or semi-automatic gun that can be mounted on the robot? We've got an air compressor, but it takes a while to build up pressure, and we have to launch ten balls in the first ten seconds, so mechanically based designs are preferred. (We've also got oodles of servomotors, winches, and the like, so we can make mechanisms that can do anything your hands can.) Accuracy is VERY important, perhaps more so than range. Also, remember that the balls must be re-fed into the cannon after every shot; if we could make it possible to get balls off the ground and into the magazine, that would be ideal.
So, any ideas? You all seem to have a much better grasp of foam launching technology than I do, and the engineer working for us is employed by a NERF-free corporation.