Many ball machine builders (including me!) use the same basic idea of an element I call a Seesaw. For this element, a ball rolls back and forth on the curved track until it stops. Then the dumper releases the ball. I made an Instructable for my version of this Seesaw element. Below are the link to my Instructable, the video and some pictures.

Seesaw- A K’nex Ball Machine Element

-Knextus