Brushless Motors

What Is a Brushless Motor?

The brushless motor uses an electronic controller for switching DC currents to the motor’s windings, thus producing magnetic fields which effectively rotate in space and are followed by the rotor of the permanent magnet. The controller adjusts the DC pulses’ phase and amplitude to control the motor’s speed and torque. Therefore, this control system is an alternative to the mechanical commutator (brushes) used in most electric motors.

How a Brushless Motor Functions

The working principle for the brushed DC motor is the same as the brushless DC motor, including the internal shaft position feedback. However, the brushless DC motor contains only two basic parts: the rotor and the stator. The rotor refers to the rotating part and holds rotor magnets, whereas the stator is the stationary part and contains stator windings. In a brushless motor, permanent magnets are attached to the rotor and specialize in moving the electromagnets to the stator.

The high-power transistors are used to activate the electromagnets for the shaft turns. The controller performs power distribution by using a circuit that is in a solid state. Because of this DC motor design, there is no need for brushes. The advantage of a brushless DC motor is removing wear and tear on the brushes since very little heat will result from the rotating magnet. The brushless DC motors are therefore more expensive because of their efficiency.

Types of a Brushless Motor

All the types of brushless motors have the same working principles, but they differ in design according to the area of use. The brushless motor is found in two types: the outer rotor motor and the inner rotor motor.

Inner Rotor Design

This type of rotor is designed in a manner whereby the rotor is located in the center of the motor, and the motor’s stator winding surrounds the rotor. The heat in the motor is dissipated easily because the rotor magnets are unable to insulate heat inside. This is because the rotor is located in the core. Inner rotor-designed motors, therefore, produce a large amount of torque and are validly used all because of this reason.

This type of rotor can produce excellent acceleration and deceleration responses due to the small rotor diameter and the low moment of inertia. Because the stator is positioned near the motor surface, there is good heat radiation, allowing for a compact motor with high output power.

Outer Rotor Design

In this design, the rotor surrounds the winding, located in the motor’s core. The duty of the magnets in the rotor is to trap the heat of the motor inside and prevent it from dissipating. The outer rotor-designed motors operate at a lower-rated current and have low cogging torque. The contained moment of inertia is larger, and the responses in acceleration and deceleration are poor, although this type of design still provides excellent speed stability.

Because of this a cup shaped rotor is not well suited to nimble the movements. More magnets can be installed all because of the rotor’s large diameter and this results in an increased number of magnetic poles thus allowing high output power to be possible in a compact size.

Disk Rotor Type

In this type of brushless motor, the stator is formed by mounting the windings and the magnetic pole sensors on the circuit board. The disk rotor type motor is thin because the tabular permanent magnets are placed on the rotor surface to allow them to face the stator. The load is installed on the rotor because there is no shaft. This type maintains a stable and fixed speed with a light load. This type is generally used in disk drives for DVDs.

Applications and Uses of Brushless Motors

Brushless motors are used in areas such as for devices like computer hard drives and DVD players. They can also be used to power the small cooling fans found in electronic devices. They are also used for gramophones and can be used in cordless power tools to increase efficiency.