The Ping-pong catapult

We have decided to build a catapult which swings ping-pong balls. Our catapult has a spoon-like launcher on which the ball is set. We will set a light sensor next to the launcher and a LED light directed toward it, which will cross the place where the ball will be placed. When the ball is on the launcher, the light no longer reaches the sensor, which gives the Arduino a signal to launch the catapult. The launcher will be moved by a servo-motor. The catapult also has an ultrasound sensor which makes sure there is nothing in the trajectory before the launch.

Our initial idea was to have an NFC-tracker attached to the ping-pong balls, and an NFC-sensor with the catapult that would recognize those balls with tracker and then shoot them. Later we decided that it would be more practical to simply have a weight sensor which would recognize that there was something (a ball) on the launching pad and then launch the catapult. Finally we decided to replace the weight senor with a light sensor, because we found it difficult to set the location of the weight sensor in a way that would protect it from being beaten during the launch.

At first we were also going to build a separate launching pad for the ball and then hit it with a swing. However, we found the spoon-like launcher to be more practical solution, because it would have been difficult to correctly adjust the place of the ball and the hitting angle of the stick in order to enable a good swing.

Image 1: A sketch of the catapult

Image 2: Another sketch showing some mechanical details, the electronic components and the bill of materials