Dog entertainment

My two girls are avid ball chasers,
lab/collie & collie/kelpie,
and am wanting to know if anyone has seen
an easy or cheap AUTO ball throwing device.
ie, dog drops ball on scoop,
dog treads on lever,
ball flies through air,
dog retrieves ball and starts all over again.
Design pro's and cons::
I have considered springs, tensioned by dog weight (more training for dogs,
maybe not much power)
Electric with switch (electric-dogs-weather- Hmmm??)
Minimum moving parts, maximum entertainment for dogs.
This is not being designed to detract from any outings or walks etc, but as
an addition.

Thanks for any ideas.
Hairy.

Hairy (love your e-name.... <grin>), I have seen a homemade wooden box
powered by a bungee cord... using a section of soup can for the cup on
the power arm.... Play with the idea... if you are of mechanical
bent.... or maybe you know someone who is good at figuring such things
out. Just one ball at a time, but, what the hey, it worked!

Jo Wolf
Martinez, Georgia