I was looking at doing something very similar, albeit with mouse micro switches. For the internals I was debating on

BastardKB

or

jfedor2

I eventually landed on Ploopy and qmk’d a kb layer for my mouse button needs.

Ploopy BTU Print File

I did alter it a bit, maybe enough to warrant a remix version. I split the model from two to three pieces. I found the distance between the sensor and ball to be very sensitive and a mm would take it from being great to being unusable. Since I used a Kensington ball and not a pool ball, having a third section allowed me to dial in that distance without having to reprint the entire top. It also removed an overhand that would have otherwise needed printing supports.

Thanks for sharing it, otherwise I'd still be trying to build one just like it!

That's a Ploopy nano pcb in a printed BTU base. I needed something more symmetrical than the original Ploopy one. I also used a 55mm trackball Kensington because I liked the size better.

I'm using it for navigation to my symbol, number, and shortcut layers.