I built this Catapult using Microduino mPie 7 in 1 kit.
On the board put together the pieces as shown in the picture below. The first yellow piece is the Power, next is button, then timeout, Slide dimmer & Servo at the end.
Attach the Catapult arm to the servo with help of a rubber band.
Attach the above part onto the black block and connect the wires to the servo block.
Complete the catapult parts with help of the cardboard pieces. Slide the switch of the slide dimmer to move the catapult.
Congratulations! you just built a Catapult.