Introduction to Brushless Motors - Canadian Woodworking Magazine

Introduction to Brushless Motors

Brushless motors have been around for quite some time, but only recently are they being used in power tools, particularly drill/drivers and impact drivers. Over the coming years you can expect to see more manufacturers adapting this technology. As the technology matures, and if there is sufficient demand for brushless technology among consumers, then we may see an even wider range of its use in the cordless power tool sector, including circ saws, recip saws, multi-tools, angle grinders, and the like.
 

Brushed Motors 

A typical brushed motor consists of wires, carbon brushes, a stator, an armature, and a commutator. The stator and brushes are stationary, while the armature and commutator rotate together on the motor drive shaft within the stator.

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Typical brushed motor
 
The stator is essentially a fixed magnet or electromagnet. The armature, or rotor, rotates within the stator, and is connected to a drive shaft and commutator. Brushes provide the electrical connection between the power source (the battery) and the commutator, which reverses the direction of current flow to the armature so that the magnetic fields maintain rotation. And it's that rotating force that produces torque.
 
One of the main disadvantages of a brushed motor is that the brushes constantly remain in contact with the armature - this creates friction (which accounts for the sparking that you see through the vent holes on a brushed power tool) and heat. Both of these reduce the efficiency of the motor. The constant friction between the brushes and the commutator wear each other down, which adversely affects motor performance - and where a motor is subject to excessive heat build-up it can lead to motor failure. 
 

Brushless Motors

A brushless motor does away with the brushes and the commutator. Like a brushed motor it has permanent magnets and electrically induced magnets (the stator). However, in place of brushes (that provide the electrical connection) and the commutator, a brushless motor uses an external electronic speed controller (essentially a circuit board) that creates the revolving magnetic field between the two magnets and causes the shaft to spin.

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Typical brushless motor
 
A major advantage of this system is the reduction of friction inside the motor, which means less wear on internal components and less heat build-up, resulting in a longer motor lifespan. Like brushed motors, they can heat up, particularly under a heavy load - however, they can be more efficiently cooled. 
 
Because the electrical connection is controlled digitally, rather than mechanically (by brushes) brushless motors run more efficiently, transferring more power to the drive shaft. The electronic speed controller, working in tandem with the digital controller in the lithium-ion battery, regulates the amount of power required for a specific task – as more resistance is encountered it provides more power. As resistance decreases it reduces the draw on the battery, conserving energy.
 
Another important feature of brushless motors is that they're small - which reduces overall tool weight. 
 
If you were to take out the brushless motor on your drill/driver it would consist of a fan (which serves to cool the motor), a permanent magnet, an electronic speed controller (that serves the function of the brushes and commutator on a brushed motor), and an electrically induced magnet (the stator).
 

Why Brushless is Better

  • Smaller and lighter than brushed motors.
  • Electronic speed controller provides increased control over speed and torque settings.
  • Less friction, heat and amp draw means a longer run time.
  • More efficient use of energy.
  • Less energy required to run the motor.
  • Virtually maintenance free.
  • Longer tool life.

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Bosch brushless PS22-02 cutaway