UC San Diego

This paper presents an original design for a multimodal hopping robot. The robot harnesses passive stability to reduce the complexity of the control problem required to keep upright during the hopping motion. The nominal mode is an upright rover mode, which behaves as an inverted pendulum. When the rover encounters an obstacle, it changes modes. The wheels are gimballed perpendicular to the robot body, and spin up to generate a stabilizing gyroscopic reaction torque. In this mode, the robot behaves like a spinning top. The robot enters a passively stable regime of steady precession at a constant nutation angle. By triggering a hop at a chosen point in the precession, the robot can traverse obstacles larger than its wheel diameter. The paper also examines the theoretical underpinnings of the dynamic system in both the rover and top modes. Lagrange equations and Routh's method are used to obtain the equations of motion for the top mode. The stability of the steady precession is examined, and a control scheme for maintaining a constant rotor speed is found. The equations and controls for the rover mode are found via state space analysis. The design process and current mechanical system of a physical prototype are explained. The control scheme is implemented using a minimal set of sensors. The robot is controlled by a Texas Instruments microprocessor, which allows for untethered control. All systems are powered by an onboard battery pack, allowing the robot to function as a standalone system