A TESTBED FOR STUDENT RESEARCH AND DESIGN OF CONTROL-MOMENT GYROSCOPES FOR ROBOTIC APPLICATIONS ASEE...

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


NASA Microgravity Research Aircraft

Space-Robotics

• Robotic Arm Technology– Satellite assembly– Massive cargo relocation– Spacecraft repair


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?


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 RWAs1,2

– CMGs produce greater torque for less energy

0rotorE h

out

h


1. Carpenter, Peck, 20082. Van Riper, Liden, 1971

Comparison of CMGs to direct drive needed to bring CMGs into robotics

h

gτ

outτ


Joint motor CMGs

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 RWAs1,2

7

R1j

j

-R1

R1

-R1

CMG

1. Carpenter, Peck, 20082. 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


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!

22121211 CMGP 2211Joint P


CMG power has not previously been compared to direct drive for robotics

Testbed Specifications


• 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


DC Motor

Gear

CMG

hr1

hr1+hr2

C1+C2

C2 C1

Benefits


• 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


• Additional Focuses:• Optimizing CMG size• Real-time data collection

and analyses• Control laws for N-link

robotic arm

Single link Two links

Acknowledgements

• Space Systems Design Studio– Dr. Michele Carpenter

• Cornell Leadership Alliance

• Cornell 2007 CMG team– Mike Nagele– Nicole Monahan


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

t̂

2 22 1

1

2rotor rE I

out

h

h


A TESTBED FOR STUDENT RESEARCH AND DESIGN OF CONTROL-MOMENT GYROSCOPES FOR ROBOTIC APPLICATIONS ASEE...

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