CMG:

Path: SC/Actuator

% Simple CMG model. Assumes a tach loop controls the CMG momentum. 
   When the alpha and beta angles are zero the CMG momentum vector is

   hCMGBase = [0;H;0];

   The model can accommodate any  number of CMGs. To simulate single gimbal
   CMGs just set one angle and one rate to zero.

   The torque and momentum units are the same as the input momentum units.

   action                  u
   ----------           -------
   initialize           u.h        (n)      Scalar momentum
                        u.b        {n}(3,3) Transforms from CMG base to body 
                        u.alpha    (n)      Inner gimbal angles (rad)
                        u.beta     (n)      Outer gimbal angles (rad)
                        u.alphaDot (n)      Inner gimbal angles rates (rad/sec)
                        u.betaDot  (n)      Outer gimbal angles rates (rad/sec)

   Only the .h field is required.

   set gimbal rates     u.alphaDot (n)      Inner gimbal angle rates (rad/sec)
                        u.betaDot  (n)      Outer gimbal angle rates (rad/sec)

   set gimbal angles    u.alpha    (n)      Inner gimbal angles (rad)
                        u.beta     (n)      Outer gimbal angles (rad)

   action                  y
   ----------           -------
   get torque           torque     (3,1)    Torque in body frame
   get momentum         momentum   (3,1)    Momentum in body frame

--------------------------------------------------------------------------
   Form:
   y = CMG( action, u )
--------------------------------------------------------------------------

   ------
   Inputs
   ------
   action        (1,:)   Actions
   u             (1,1)   Input depends on action

   -------
   Outputs
   -------
   y             (1,:)   Output depends on action

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