I just wanted to make something for my cat and as you can see by the pictures she loves it. Slight side effect of making this is that you may hear it getting flung around in the middle of the night if yours is anything like mine and gets the zoomies at 3AM.
It took quite a few prototypes to get it to this level of reliability and fresh off the printer the smaller ball is a little difficult to get threaded together depending on the filament that you use. when dealing with tolerances this small for the threads a number of things could be the cause but some filaments gave me no issues at all and some took a little patience for the first connection but after that they were fine.
I hope that your cats enjoy this as much as mine does