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A Testbed for Student Research and Design of Control-Moment Gyroscopes for Robotic Applications

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 CMG- actuated 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.

Introduction

Experiential learning is an important part of an engineering education. Some universities are able to build and launch operational satellites1. The Microgravity University at NASA’s JSC in Houston, Texas, allows students to perform experiments in a weightless environment without the launch risks of actual spaceflight. Recently, student teams at Cornell University tested a robotic arm using control moment gyroscope technology as part of the Microgravity University2.

The successes of the International Space Station and the NASA Space Shuttle depend on the capabilities of their robotic arms. Mission operations can be driven by current robotic arm technology. Robotic arms are used for everything from relocating massive cargo to manipulating delicate and sophisticated pieces of equipment, such as space telescopes and communication satellites. Because robotic arms have such a vital role in space ventures, advances in robot technology are critical in enabling space programs to expand their realm of possible missions. The use of control-moment gyros (CMGs) in space robotics is presently in the early proof-of-concept stage3. CMG technologies per se are not new and have been used for spacecraft attitude control4. As joint actuators, they offer significant benefits to robotic-arm technology for space applications in cost and energy. The principal advantage of CMGs in robotic arm

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Soto, A., & Brown, D., & Peck, M. (2009, June), A Test Bed For Student Research And Design Of Control Moment Gyroscopes For Robotic Applications Paper presented at 2009 Annual Conference & Exposition, Austin, Texas. 10.18260/1-2--5572