What the video below to see it in action!

Use a pen to hold the 2 balls/marbles/bearings for a clean start and watch the bumpy road win!

Ball size/weight/starting position/layer height all affect results. I used ball bearing and practived dropping spots until I got consistent results. 

I created many versions testing, but if you have more precise technical drawings of what the exact path looks like I will re-open this project and update the model.

I did my best to copy what I saw on this low-res video, but I'm sure my arcs aren't perfect. Thanks for being curious.