Moving to belts and dropping rotation might not be inevitable after all. Instead we could incorporate a system that adds rotation too
The simple pitch and roll solution with belts looks like this :
This is the view from the bottom of the sphere, motors on the sides and the belts are the blue lines.
Instead, if we have motors that are off the axis but aligned they could not only pitch the sphere but depending on how much each side pulls, rotate it as well.
Belts are blue and green here.
As I was drawing it I realised a similar system already exists, albeit not in this field. It’s used in some 3D printers and could be adapted to fit our needs here. It wouldn’t give us full rotation, I guestimate only 90 degrees yaw and I’ll have to figure out how to avoid interference with the belts but it’s an idea worth considering.
Check out CoreXY to read about Cartesian Motion to your hearts content 🙂