How does a Brushless Drive or Motor Work?

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Brushless Drive

The brushless drive or motor is an electric motor with direct current and with a permanent magnet rotor and a rotating magnetic field stator. Unlike a brushed motor, it does not brushes on the motor shaft in order to operate. The switching of the current circulating in the stator windings; therefore, the variation in the orientation of the magnetic field normally generated by the brushes occurs electronically. This means lower mechanical resistance and the elimination of the possibility of sparks due to the increasing speed of the rotation. Moreover, this considerably reduces the need for periodic maintenance.

The installation of a brushed motor is, in general, simple and inexpensive, but it has many problems:

  • The brushes eventually wear out.
  • As the brushes are making/breaking connections, sparks and electrical noises are obtained.
  • The brushes limit the maximum motor speed.
  • Having the electromagnet in the center of the engine makes it harder to cool down.

Therefore, the use of a brushless drive is an optimal choice.

A very similar motor is the stepper motor – or step/stepping motor – which differs from the brushless drive or motor because the stator is not powered entirely but cyclically feeds the various electromagnets so as to generate rotation. In a brushless motor, the rotor has no winding and is instead equipped with permanent magnets, while the magnetic field generated by the windings on the stator is variable.

Since the motor operates in direct current, in order to realize the rotation of the magnetic field generated in the stator, an electronic circuit, composed of a bank of power transistors controlled by a microcontroller that controls the commutation of the current, controls the inversion of current and therefore the rotation of the magnetic field.

Here are the advantages and disadvantages that brushless drives or motors present:

Advantages:

  • The first significant advantage is the expected life of the motor. Since the brushes are the “weak point” of an electric motor, a brushless motor will last longer.
  • The absence of brushes also eliminates the main source of electromagnetic noise present in other electric motors.
  • The footprint is limited compared to the power that they can deliver and above all compared to the torque that these motors are able to deliver.
  • In terms of efficiency, brushless motors always work at their highest performance conditions.
  • In this type of motors, the permanent magnets are positioned on the rotor and are made with special materials that allow having very low rotor inertia, which allows having an extremely precise control both of speed as well as of acceleration.
  • There is no spark and much less electrical noise.
  • These motors are very easy to cool down.

Disadvantages:

  • The main disadvantage of this type of motor lies in the higher cost, but it is often possible to recover this cost thanks to the greater efficiency during its life.
  • Unlike brush motors, the control is carried out electronically by a controller, an electronic device supplied by the motor manufacturer or by third parties, so the cost of the control system must be added to the cost of the motor.

And where are brushless drives used? These type of motors can be used in different sector:

  • Transport: for example in electric and hybrid vehicles, and personal transporters. Moreover, also in electric bicycles, brushless motors are used. In this case, brushless motors are more efficient.
  • Cordless tools: for example in leaf blowers, drills, and saws. In this case, brushless motors are easier to the handheld.
  • Heating and ventilation: in this case, the use of brushless motors allows to reduce the power required by the system to operate, therefore decreasing the energy costs.
  • Industrial engineering: here, brushless motors are used for motion control, positioning and actuation systems.

If you have doubts about brushless drive and motors and you want to know if they are the best solution in your case, Axor Industries is the expert to contact.

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