Motors govern our lives in multiple ways. They are the basic machines assisting us from simple transportation to sophisticated movement of a large variety of tools. There are many types of motors, both for operating on alternating current and direct current supplies. Of the motors operating on direct current supplies, there are two major categories—brushed and brushless—with differences in their construction, structure, and operation affecting their performance.
Both brushed and brushless motors operate using the principles of EM or electromagnetic induction, converting electrical energy to mechanical rotary movement. Both types of motors allow electricity to pass through copper windings, thereby creating interacting electromagnetic fields that cause the rotor to rotate and produce mechanical energy. However, their design concepts are different, making them differ in performance, cost, and maintenance.
Of the two, the brushed motor is the older design, having been available for over a century. These have a simplistic structure with two coils, one on the stator and the other on the rotor. A pair of carbon brushes delivers power to the coils on the rotor. Typically, brushed motors have four major parts—stator, rotor, commutator, and brushes.
The stator is the stationary part of the motor. It contains the stator windings or permanent magnets. The rotor, as the name suggests, is the rotating part, attached to the shaft. It has several rotor coils that, when powered, create an electromagnetic field to interact with the EM field of the stator. The commutator is a sectioned metal ring to ensure each rotor winding receives power as it rotates. It helps in reversing the polarity of the current through the rotor windings every half turn of the rotor. Brushes are stationary carbon electrodes that feed power to the rotor windings through the commutator.
As current passes through the stator and rotor windings, depending on their relative positioning, their EM fields either attract or repel each other. This makes the rotor turn, and thereby, changes the commutator connection to the brushes. The current flow now passes through a newer rotor coil and propels the rotor further in the same direction as before. This goes on until the rotational friction balances the EM interaction, at which point the motor’s rotational speed stabilizes.
Once transistors became more common in electronics, brushless motors started gaining popularity. Brushless motors also have four major parts—stator, rotor, sensors, and control circuits. Here too, the stator is the stationary part of the motor and has several copper coils, which, when powered, generate EM fields. The rotor is the moving part attached to the shaft of the motor. But rather than coils, the rotor has permanent magnets that generate their own EM fields. Hall-Effect type sensors sense the position of the coils with respect to the rotor magnets. The control circuit replaces the commutator and brushes to decide which coils in the stator should be powered next.
Brushless motors are more efficient as compared to brushed motors, and they provide higher torque, faster acceleration, lower noise, and lower maintenance. However, brushless motors are more expensive and heavier.
