A TESTBED FOR STUDENT RESEARCH AND DESIGN OF CONTROL-MOMENT GYROSCOPES FOR ROBOTIC APPLICATIONS ASEE Annual Conference & Exposition – Austin, Texas June 15, 2009 Albert Soto, Daniel Brown, Mason Peck Space Systems Design Studio at Cornell University

Overview Experimental Learning Space-Robotics Drive Design Momentum Actuators Reactionless Robotics Specifications & Design Student Benefits Space Systems Design Studio ASEE June 2009

Experimental Learning Fundamentals of Professionals Research Project-Oriented Learning –Teamwork –Self-confidence –Opportunity to apply coursework –Experience –Visualize professional career –Retention in engineering Limiting Factors of Aerospace Research –Infrequent microgravity flight trips –Risks in spaceflight launch –Limited resources Space Systems Design Studio ASEE June 2009 NASA Microgravity Research Aircraft

Space-Robotics Robotic Arm Technology –Satellite assembly –Massive cargo relocation –Spacecraft repair Space Systems Design Studio ASEE June 2009

Actuator Design What is a Drive Design? Direct Drives –Conventional actuators for robotic arm joints Control-Moment Gyroscopes (CMGs) –Traditional spacecraft attitude control CMGs vs. Direct Drives –Reactionless actuation –Energy advantage? Space Systems Design Studio ASEE June 2009

Momentum Actuators Control-Moment Gyroscope (CMG) –Constant-speed rotor –Gimbal the rotor about g-axis to change angular-momentum vector h –100x less power than RWAs 1,2 –CMGs produce greater torque for less energy hh  out hh Space Systems Design Studio ASEE June Carpenter, Peck, Van Riper, Liden, 1971 Comparison of CMGs to direct drive needed to bring CMGs into robotics

Space Systems Design Studio ASEE June 2009 Joint motorCMGs Torque reacted on spacecraft No actuator torque reacted on spacecraft Reactionless Robotics Actuator reaction torques Inertial reaction forces –From D’Alembert’s principle Benefits of CMGs –Reduce disturbances and low frequency vibrations –Isolate subsystems –Increased agility of robot –More power efficient than RWAs 1,2 7 R1R1 jj  j -R 1 R1R1  CMG 1.Carpenter, Peck, Van Riper, Liden, 1971

Reactionless Robotics in Space Robotic manipulators –Space construction and repair Pointing tasks –Independently orient cameras, sensors, transmitters, solar panels, etc. Reduced propellant use in attitude control –Reduce launch mass –Extend mission life DARPA SUMO spacecraft & Cornell CMG team Space Systems Design Studio ASEE June 2009 Efficient use of limited spacecraft power

Power Requirements Power equations of output torques: –in terms of the joint torques and velocities Power equations do not equal! Space Systems Design Studio ASEE June 2009 CMG power has not previously been compared to direct drive for robotics

Testbed Specifications Space Systems Design Studio ASEE June 2009 Planar two-link robot –+/- 90 deg range Dually actuated –CMGs from robot arm –DC motors at joints Air bearing levitation Wireless control/data acquisition Expandable to 3-link robot Removable base link

The Scissored-Pair CMG Configuration Space Systems Design Studio ASEE June 2009 DC Motor Gear CMG   h r1 h r1 +h r2  C1 +  C2  C2  C1

Benefits Space Systems Design Studio ASEE June 2009 Student introduction to: –Reactionless robotics –Momentum actuators –Dynamics of CMGs –Research –Ground testing of space-systems –Mechanical design and fabrication Experience for excellence in engineering Advances faculty and graduate students –New experimental hardware –Design groups

Future Possibilities Space Systems Design Studio ASEE June 2009 Additional Focuses: Optimizing CMG size Real-time data collection and analyses Control laws for N-link robotic arm Single link Two links

Space Systems Design Studio ASEE June 2009

Acknowledgements Space Systems Design Studio –Dr. Michele Carpenter Cornell Leadership Alliance Cornell 2007 CMG team –Mike Nagele –Nicole Monahan Space Systems Design Studio ASEE June 2009

Momentum Actuators CMGs are part of a larger class of actuators Internal momentum change provides output torque A spinning body resists change –Magnitude or direction of spin Reaction Wheel Assembly (RWA) –Rotor fixed to spacecraft –Vary rotor speed magnitude –Large energy change of rotor  out hhhh Space Systems Design Studio ASEE June 2009