DCMotor:

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   DC motor model.
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   Form:
   u = DCMotor( v, omega, d )
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   ------
   Inputs
   ------
   v   	      (:)     Input voltage
   omega         (:)     Angular rate (rad/sec)
   d             (:)     Data structure 
                         .kT  Torque constant
                         .r    Resistance
                         .iMax Maximum current
                         .iMin Minimum current
                         .kG   Power amplifier gain
                         .vMax Maximum voltage

   -------
   Outputs
   -------
   u   	      (:)     Voltage

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