In effort to make interactive “Toys” for my robots I created with a catapult built for my LEGO Mindstorms robot back in the day.
I used a LEGO DC motor with the cable I prepared for Cardbot initially, and used a role of tape to weight down the base of the contraption. On the Breadboard I used an ultrasonic distance sensor to enable the robot to shoot the catapult. The logic is handled by the arduino and the simple H bridge to power the DC motor externally to protect the arduino.
Here a small video of it in action: