Postural stability of a human riding a unicycle and its emulation by a robot

A unicycle is an inherently unstable system in three dimensions. As shown by a human riding a unicycle, the rider's complicated successive dynamic control actions are needed for the postural stability control of the unicycle, and the rider's actions for stability are quite nonlinear and jerky. By emulating the performance of a human riding unicycle, we can do tests of different classic and modern control methods used in 3-D inherently unstable systems, where a theoretical analytical methodology for the stability of this unstable system is expected to be developed. Because the longitudinal and lateral stability are coupled to each other in this system, and no actuator can be used directly for the control of unicycle's posture in 3-D (pitch, roll, and yaw angles), it is not easy for us to emulate the performance of a human riding a unicycle. In this paper, a unique unicycle robot is developed. The postural stability control of a human riding a unicycle in 3-D is realized by this robot.