True, but a robot on wheels (while unpowered of course and parallel to our own wheels) should theoretically have a lower coefficient of friction than the chair? Please correct me if I'm wrong.
Not necessarily. You appear to be using the AM HiGrip Wheel (if I'm not mistaken), and assuming your carpet is standard FRC carpet, the CoF is listed as 1.067. I'd guarantee that roller chair wheels have significantly less grip than that.