Attitude Control for Underactuated Hopping Robots Using Nonlinear Output Zeroing Controller

This paper proposes a nonlinear control of aerial attitude regulation for hopping robots that have a freely-rotating body with a pair of actuated arms that are connected to each other. These kinds of robots are so-called underactuated robots. The proposed controller is based on an output zeroing control that stabilizes angular momentum and the body pitch angle to be zero. Compared with attitude stabilizing methods using axisymmetric reaction wheels driven by a linear control law, utilizing arms for attitude compensation, which is not axisymmetric, will achieves more natural motions like animals. As the first stage of the development, a controller has been designed for an underactuated inverted pendulum model, where the robot body is supported a freely-rotating joint and the arms is actuated by a motor. The control law is simplified based on simulation analysis so as to be implemented to low-cost microcomputers. To show the validity of the proposed method, an inverted-pendulum-type robot with a pair of arms driven by an inexpensive hobby-use motor has been prototyped, the attitude of which is measured by using a 9-axis motion sensor, and the control law has been implemented to a microcomputer, Renesas RX63N (GR-SAKURA II). Experiments to control the pitch angle of the robot has been conducted, and the experimental results showed that the proposed method well works to stabilize the amplitude of the pitch angle to be less than about ±13 degrees.