Space Applications
Since this change in angular momentum generates a gyroscopic torque that is purely a constraint torque, it does no work, and therefore requires virtually no input power. This low-power feature of a CMG makes it an attractive alternative to a reaction wheel (RWA), which applies torque simply by changing its rotor spin rate. CMGs have been used for many years to efficiently produce high torques in large spacecraft, including agile earth-imaging satellites, Skylab, MIR, and the International Space Station.
Should the arm operate in a grounded configuration, the angular momentum of each body/joint is constrained to remain in a fixed direction. Should the arm operate in space, the arm and CMG’s must be configured in a way such that the angular momentum of each joint remains (rather than is constrained) in some desired orientation. CMG’s grouped in scissored pairs meet this requirement.
For a brief description of the dynamics and space applications of CMGs visit tam.cornell.edu