What is variable reluctance steeper motor? Its types, working, construction, advantages, disadvantages & Applications

A variable reluctance stepper motor is a type of electromechanical motor that converts electrical pulses into discrete mechanical steps. It operates based on the principle of variable reluctance, which is the tendency of a magnetic object to move towards a position where the magnetic flux is minimam.

Types of variable reluctance stepper motor:

  1. Single Stack Variable Reluctance Motor: This type of motor has a single rotor and stator stack. It typically has a low torque and step resolution but is simple and inexpensive to manufacture.
  2. Multi-Stack Variable Reluctance Motor: This type of motor has multiple rotor and stator stacks, which are interleaved to increase torque and step resolution. It provides higher torque and better performance compared to a single stack motor, but it is more complex and costly.

Working Principle of variable reluctance stepper motor:

A variable reluctance stepper motor consists of a rotor with salient poles and a stator with windings. The stator windings are energized sequentially, creating a magnetic field that attracts the rotor teeth towards the energized stator pole. As the rotor teeth align with the energized stator pole, the magnetic flux through the rotor is minimized, and the rotor moves to the next aligned position. This process is repeated to achieve continuous rotational motion.

Construction of variable reluctance stepper motor:

A variable reluctance stepper motor typically consists of the following components:

  1. Rotor: It is the moving part of the motor and is made of ferromagnetic material. It has salient poles or teeth that interact with the stator poles.
  2. Stator: It is the stationary part of the motor and is made of ferromagnetic material. It has windings that are energized to create a magnetic field.
  3. Windings: The stator windings are wound around the stator and are connected to the power source. They are energized sequentially to create a rotating magnetic field.
  4. Driver: It is an electronic circuit that controls the sequence and duration of the current pulses applied to the stator windings.

Advantages of variable reluctance stepper motor:

  1. Simple construction: Variable reluctance stepper motors have a simple construction with fewer components, making them cost-effective and easy to manufacture.
  2. High reliability: They have no brushes or commutators, which reduces the wear and tear, resulting in higher reliability and longer lifespan.
  3. High torque-to-inertia ratio: Variable reluctance stepper motors have a high torque-to-inertia ratio, which makes them suitable for applications that require quick acceleration and deceleration.
  4. Precise positioning: They can achieve precise positioning and can operate in open-loop mode, eliminating the need for complex feedback devices.

Disadvantages of variable reluctance stepper motor:

  1. Lower torque compared to other stepper motor types: Variable reluctance stepper motors generally have lower torque compared to other types of stepper motors, such as permanent magnet stepper motors.
  2. Lower step resolution: They typically have lower step resolution due to the limited number of rotor teeth, which may limit their suitability for applications requiring very fine positioning.
  3. Higher power consumption: They may have higher power consumption due to the sequential energization of the windings, which can result in lower overall efficiency compared to other motor types.
  4. Vibrations and noise: Variable reluctance stepper motors may exhibit vibrations and noise during operation due to the rapid switching of the stator windings, which can impact the performance in certain applications.


  1. Industrial Automation: VR stepper motors are widely used in industrial automation applications, such as CNC machines, 3D printers, and automated assembly lines. They are used for precise positioning and motion control tasks, where accurate and repeatable motion is required. VR stepper motors are capable of producing high torque at low speeds, making them ideal for applications that require high precision and fine control.
  2. Automotive Systems: VR stepper motors are used in various automotive systems, such as throttle control, fuel injection, and HVAC (Heating, Ventilation, and Air Conditioning) actuators. They are used to control the position of valves, flaps, and other mechanical components with high accuracy, ensuring proper operation of the systems and improving overall vehicle performance.
  3. Robotics: VR stepper motors are commonly used in robotics applications, such as robotic arms, grippers, and humanoid robots. They provide precise motion control and can be used for both linear and rotary motion, making them suitable for various robot joint configurations. VR stepper motors are used for tasks that require precise positioning and movement, such as picking and placing objects, performing delicate manipulations, and navigating complex environments.
  4. Aerospace and Defense: VR stepper motors are used in aerospace and defense applications, such as satellite positioning systems, antenna positioning, and missile guidance systems. They provide accurate and reliable motion control in harsh environments, such as high temperatures, high altitudes, and extreme vibrations.

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