I had a project like this in College. It was the final for my volume and design class. We had to build something that would keep a marble in motion for exactly 30 seconds. I had gone up to my grandparents for spring break and over dinner, I explained this project I needed to work on. The next morning I had woken up, and my grandpa had built one for me! He was fine tuning it by making little speed bumps with glue to slow the marble down. Best grandpa in the world!