Design, analysis and implementation of control moment gyroscope (CMG) mechanism to self-balance a moped bike

Abstract

This paper presents the design and implementation of the control moment gyroscope (CMG) mechanism on the Okinawa IPRAISE Scooter, an electric moped, to self-balance it with or without a rider. The scooter can be balanced in static as well as in moving condition so that it won’t fall over. Higher torque amplification and momentum storage capacity makes CMG superior over other mechanisms like reaction wheel, mass balancing, controlling the movement of front steering, etc. CMG mechanism consists of a pair of spinning discs, i.e., flywheels which are driven continuously by DC motors about vertical z-axis. An encoder deployed to sense the tilt angle about longitudinal y-axis provides feedback to the PID controller. The controller, in turn, produces restoring torque by gimbal action with the help of a pair of stepper motors mounted on horizontal x-axis to maintain the scooter in vertical position. Thus, using gyroscopic effect of two spinning flywheels, CMG mechanism generates reactive torque which assist the user to balance the bike in several riding modes. Stack up calculations were performed to make a tradeoff between moment of inertia and mass of flywheels to arrive at the dimensions of the flywheel. Subsequently, 3D model of the mechanism is developed with the help of CREO. The mechanism is analyzed and simulated in ANSYS. Mock-up samples were procured. It is then mounted on the scooter and tested. One optimum location is finalized based on the center of gravity. Finally, the bike is found to balance itself resulting in a compact and robust mechanism giving safe and comfortable ride. This, however, comes at an additional ten percent power consumption, twenty-five percent increase in weight and nine percent increase in cost. Further improvement can be done by reducing this parameters by using lighter materials and small size motors.