CMG Description
A Control Moment Gyroscope (CMG) is a torque generator primarily used for the attitude
control of a spacecraft. A CMG consists of a constantly spinning rotor with gimbals that
change the direction of the rotor’s angular momentum vector.
One of the fundamental requirements for this project is to actuate the arm with
control moment gyroscopes (CMG’s). CMG’s are an efficient and low power mechanism for momentum
exchange. While there are many typical configurations of CMG’s, when arranged in scissored pairs
CMG’s are easily modeled and controlled. The arm is easily modeled as three single bodies with
single degrees of freedom. The arm is comprised of 3 rotational joints, with orthogonal degrees
of freedom. Each joint contains one scissored pair of CMG’s for imparting motion.
A CMG consists of a spinning rotor and one or more motorized gimbals that tilt
the rotor’s angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic
torque that rotates the base body on which the CMG is mounted.
CMG’s require a torque to induce the vector change in the rotor’s angular momentum
(a torque about the gimbal axis, a gimbal torque). Due to Newton’s law, this torque applied to the
CMG by the body is also applied by the CMG on the body (in accordance with the conservation of
angular momentum). When a CMG is gimbaled, its angular momentum vector changes direction, it has
traded angular momentum with the body to which it is attached. In a scissored pair, two will in
angular momentum which always falls along a straight line.
For an addtional description of the dynamics and space applications of CMGs visit tam.cornell.edu