Kevin Hjelden and his friend Joe built this autonomous shooter for this year’s Defconbots competition. They described the build before they started:
The electronics for this project are going to be relatively simple as well. To control the three servos (pan + tilt + firing), we are going to use the Pololu 8-channel servo controller. Normally we might use an atmega to do the control, however I already created code to control the pololu controller for another project and it’s really inexpensive/easy to use. If it required more complicated feedback or logic, a microcontroller might have been the better choice, but in this case it wasn’t, so the right decision was just to use the Pololu controller. To control the valve, we had two options. One was to use another channel on the servo controller and something like a Banebot motor controller to apply power to the electronic valve, the other was to use the servo that pushes the plunger to push a switch that opens the valve. The latter option was chosen.