Very cool.
Are you using a micro servo, or a standard size? Some micros have nice torque. Have you thought about using a photo strobe for the light source? (This is how I want to build mine, still looking for uber cannon though). You could use a blue (light) filter, then the photo strobe. As far as a batter/power source, that could go into the shoulder pack. If you used a LithoPolly battery, you could get a long life and a nice cyclic rate. I was planing on using somewhere around a 2,400 mil amp battery for my setup.
Just a thought though,
Again, very cool on the cannon.