[EricH]

Are you starting the ball directly between the wheels? If you are, you shouldn't be. Give it a little speed coming in.

Also, what motors are you using? Some motors (say, the window motors) are not good for this type of system.

Oh, and popnbrown--the infamous Poof balls (shelled) were the victims in 2006. If you raided your local Walmart in the hunt for the Orbit balls, you may have seen the unskinned version.