Scissored-Pair Control-Moment Gyros: A Mechanical Constraint Saves Power

Scissored-pair control-moment gyros, uses a mechanical constraint, such as gears or a mechanical linkage, to enforce the gimbal symmetry. This control moment has been compared with a scissored pair of independent CMGs, having its own gimbal motor, which needlessly uses power to react to workless constraint torque. A small satellite attitude-control system illustrates the effect of the internal torque cancellation provided by a mechanical constraint on peak torque, power and energy used. The gear has replaced the two independent gimbal motors with a single motor, resulting in improved mass and volume efficiency in the electromechanical design. Nonlinearities in the gears or mechanism connecting the CMGs may effect the results, thus actual power saving would depend on the hardware implementation. The base-rate effects are cancelled internally through the mechanical coupling. This may have implications for all null motions of arbitary CMG arrays.