Tennis Ball Launcher

The subject pretty much gave it away but does anyone know how to make a tennis ball launcher out of a pringles can/items used around the house? Directions or links would be appreciated.

I am not sure if those are illegal or not, but I have heard that building and using the similar "potato gun" has been deemed legal unless you use it as a weapon. Nevertheless, you can email me at [email protected] and I would be more than happy to fill you in on how to build one of those.

The only one that comes to mind shoots flaming tennis balls.... Fun to play with, but not that practical for tennis...