Multi Stack Variable Reluctance ( VR ) Stepper Motor

The construction, step angle, advantages and disadvantages of variable reluctance stepper motor is given in this theory.

Construction of Variable Reluctance Stepper Motor

  • Figure shows four stack variable reluctance stepper motor.  
  • We can achieve low step angle by multi stack variable reluctance stepper motor. 
  • The stator frame and rotor shaft are common in the multi stack variable reluctance stepper motor. 
  • Each stack is parallel to shaft axis and its excitation is given by separate winding. 


Step angle in Variable Reluctance Stepper Motor

  • The number of stator poles is equal to number of rotor poles. 
  • If there are 20 teeth in the four stack VR stepper motor, the step angle becomes 4.50.
  • Step angle ( Θ ) = 3600 / S

       Where S = 4 ( Number of stacks ) × 20 ( Number of rotor teeth )

                     = 80

  • Therefore, Step angle ( Θ ) = 3600 / S = 3600 / 80 = 4.50

Advantages and Disadvantages of VR Stepper Motor


  • Higher stepping rate is possible
  • Low inertia of rotor
  • Light weight
  • Freely rotation of rotor


  • Nil detent torque
  • Higher efficiency for low stepping rate

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