Observations and Changes

The finished prototype serves a great conceptual example for the build. However, the materials we used are clearly far from ideal and so the functionality isn't there.

The launch platform inside the barrel spins since it is only restrained at two points and the spring is not thick enough to fill the inside of the barrel.To fix this, the final tube will be 1.5" inner diameter pvc pipe with a 3/4" compression spring. This is a tighter fit than the 2.5" can here.

Also, the fishing line will be connected to the launch platform at 4 points, every 90 degrees along the outside. This should eliminate any unwanted rotation inside the barrel. These four cords meet at the center of the spring and connect to an individual string which runs along the barrel and out the end cap. This string then moves through a track of eye-hooks which lead to a stepper motor, which compresses the spring. This component is referred to as the loading mechanism.

The string will run through a catch that is pulled into the base, in order to keep the spring compressed. The loading mechanism stepper motor then unwinds, preparing the launcher for firing. The catch is then lifted by a servo motor, releasing the compressed spring, propelling the launch platform, and firing the ping pong ball.

For this purpose the group decided that to make more room for the loading mechanism on the base plate. The entire cannon will be shifted several inches farther from the center of the base disc.

Also, the entire apparatus will be held up by 3 wheels along the outside of the base. At the center of the base is another servo which should allow for free 360 degree rotation.