gravity powered wheel design, can be made without slots, the basic idea is in the center wheel relative to a constant 1. call it a lot of things, curve translation to a relative 1. imagine a circle to fit any given curve point in the middle hub and then imagine that relative to the circle on the outside, you can see the change of the rotation vs the circle surface distances.
I suggest taking some time to consider this "fully". It allows changeable weight positions at any given point for a customizable weight path through the entire wheels rotation. And it seems relatively simple to make, in my suggestion out of plywood, bicycle wheels and fabricated steel plates with chain wheel teeth on them for the center hub.