A Test Bed For Student Research And Design Of Control Moment Gyroscopes For Robotic Applications

Abstract

The attitude dynamics of a spacecraft with an attached robot arm is a subtle problem in dynamics and control. In this work, we discuss a robotic testbed designed to engage students in addressing this example of a complex class of rigid body dynamics. A planar, multi-degree-of-freedom robotic arm is designed and constructed with sensors and wireless communication to measure and record power usage and maneuver kinematics. Each arm segment is actuated by either direct-drive motors or a scissored pair of control-moment gyroscopes (CMGs) in order to allow the power requirements and capabilities of each design in a planar system to be compared. A scissored pair of CMGs is more like a joint motor than a single CMG because the output torque is aligned with the joint axis. The simplified dynamics of a scissored pair are also more easily understood at an undergraduate level. The testbed uses an air bearing system on a sheet of glass to support the arm segments, significantly reducing the effects of gravity and friction. Prior student groups have built and flown CMGactuated robots on the NASA microgravity research aircraft. However, one flight per year provides little opportunity for feedback and design improvement. With an in-house test setup, students can design a series of experiments and verify their work throughout the year. This testbed will provide students with a research tool for exploring the differences between CMG and direct drive actuators.