Unicycles are inherently unstable vehicles and require longitudinal and lateral control including pitch and roll motion. The one wheel is propelled by the rider and provides the longitudinal motion and the pitch control of the vehicle as well. The roll control is achieved by balancing carried out by the rider since the nonholonomic constraint does not allow a lateral displacement of the wheel–guideway contact point. Usually, forces and torques are used as control inputs even if human motions are mainly position controlled by visual feedback and not force controlled. In this paper the roll motion of a unicycle is considered. The balancing is obtained by the upper body’s roll motion which is used as control input. It is shown that balancing can be modeled by an inverted double pendulum where the relative acceleration of the upper body is chosen as control variable. Due to the nominal vertical position of the unicycle running straight ahead the balancing is represented by linear equations of motion and linear control theory is applied. It turns out that from simulations and experiments that properly controlled body positioning ensures balancing, too.

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