This instructable uses a Trossen Robotics Pan and Tilt kit to construct an Arduino controlled ping pong ball cannon. The project also uses several other components from Trossen Robotics including a medium solenoid, a relay and various items from one of their Robotics Grab Bags. A joystick controls the aiming of the cannon and a pushbutton controls the solenoid that fires the cannon.
Arduino board (I used the RobotGeek Geekduino)
2.1mm barrel jack
24 volt power supply
Large metal servo arm
The last eight items I obtained from a Robotics Grab Bag.