This instructable will show you how I made my monstrous tennis ball launcher (cannon) from mainly scrap metal and just a few things from eBay. Also included are tips and potential improvements for certain areas in both design and construction. And of course, how could I nearly forget, how to have lots of fun with it.
Propulsion source: Compressed air from compressor or foot pump (depends how lazy I’m feeling)
Barrel dimensions:90mm OD x 70mm ID x 500mm
Main ammunition: Tennis ball
Max distance of main ammunition: 100m
Secondary ammunition: anything you can stuff down the barrel with wadding at bottom
I first came up with the idea of making a tennis ball launcher to help enthuse school children (year group 9) about mathematics by getting them to aim for a target on the ground behind a wall of paper so that they had to use complex equations and mechanics principles. I did think about making a ping pong ball launcher to the same general design but scaled down as this would have been cheaper and easier, but then I thought that it would be much more fun for them to use a cannon outside. Using this instructable you could still make the ping pong cannon, but what says I love my dog more than a tennis ball cannon strapped to the roof of your car in the dog park car park.
At the end of the instructable I will include the relevant equations of motion that i hope to be able to teach the year 9's. I will also include a link to a simulator that also accounts for drag .
Step 1: The Frame
This cannon frame was constructed from 6x30mm flat bar steel but would have been easier to construct it from wood or aluminium as the bending of the steel was quite labour intensive.
The frame design is very strong, being held together with M6 bolts. Holes in the bottom parts of the frame allow pegs to be used to hold the cannon to the ground. There are also markings on the slide to indicate the angle that it will produce which will come in very helpful when predicting the distance. (Even though you can't see it in the pictures, they are there)
I started by cutting all of the bar to length and then filing them whilst clamped together to make them exactly the same length.