A self-balancing unicycle robot

Abstract

Nearly two decades after the launch of the Segway Personal Transporter, the concept of unicycles has attracted considerable attention for teaching and research purposes in both academia and industry.

This project presents the design process to the development of the mechanical, electronic and control aspects of a unicycle robot. This involves: system modelling and simulation, the design and construction of the physical system housing all the components and the implementation of the control algorithms on the relevant electronic hardware.

Balance in the pitch axis is obtained by driving the unicycle wheel such that the centre of gravity of the robot remains constantly directly above the pivot point of the wheel. Balance in the roll axis is achieved by actuation of the ywheel with enough reaction torque to counteract any falling motion.

This is implemented using two individual cascade controllers to balance the roll and pitch axes of the robot separately, with any interactions between the two considered as disturbances to the systems. A digital closed loop controller is designed using the Linear Quadratic Regulator control law to calculate the desired torques to be generated by the motors, upon feedback of motor speeds and robot tilt. The latter is obtained through sensor fusion by means of a Kalman sensor fusion technique operating on a six-axis IMU housing an accelerometer and a gyroscope. The desired torque is then fed as reference to the motor controllers for required current control.