 Kugle uses a fully coupled quaternion-based 3D model which couples the motion of all axes.The ballbots (CMU Ballbot, BallIP, NXT Ballbot, Adelaide Ballbot, Rezero) use linear feedback control approaches to maintain balance and achieve motion.The CMU Ballbot uses an inner balancing control loop that maintains the body at desired body angles and an outer loop controller that achieves desired ball motions by commanding body angles to the balancing controller.