Making a Wobbler

I have been reading this wonderful book. Matt Parker is comedian and mathematician. I realised that given the title of the book, I should actually make the things he suggests. My problem has usually been that I have read and understood the theory but never tested it. Perhaps I'd be a real physicist if I'd tried things earlier!

 I made the Wobbler from page 65. It's two intersecting circles like this. The idea is that it rolls like a wheel because if the size of the slot is exact, then it will continue to roll like a wheel because its centre of gravity remains the same height above the ground.

 By considering the two positions shown below, I was able to prove his statement that the exact size of the slot is 29.2893% of the radius. Details to follow!