My dog loves to play ball, but I found hard to play with him all day long. I build my first version ball launcher which uses fast spinning motor to spin the ball out See the link http://www.youtube.com/watch?v=hX_4McljWo4
The drawback of that is his slavor makes it no use of the device, too slippery to spin it out.
Then I came accross Dean Segovis's Make Project, I started to build the second version ball launcher for my dog. http://www.youtube.com/watch?v=7LtYAWa0xAs&feature=youtu.be
Here are some pics of the detail of the ball launcher.