Here is my automated Newton's Cradle (note: I posted this on instructables.com under JimRD). I used some fiberglass fishing pole tubes to suspend the balls and also to support the mechanism. It's all a pretty shaky affair as I can't seem to drill a straight hole but it works suprisingly well. Would be nice to add some more clackers but I could just barely align two of them and I had to tilt the whole mechanism slightly to get those working. The video describes the details pretty well.
https://www.youtube.com/watch?v=uMBUi4lI1rU