A circle motion thru driver only would need some advanced math I would think. But how I’d do it would be 4 bones for the 4 corners(each 90 degrees). Then a bone in the center. Driver switches from 1 bone to the next until it gets back to the first bone. The center bone is used as a limit distance constraint object. Set it to inside and set a distance that is smaller than the distance between the center bone to the 4 corner bones.
