BLDC Motors Guide

What Are BLDC Motors?

Brushless DC motors, also known as BLDC motors, are synchronous DC motors without brushes that utilize direct current. These types of motors feature high power and speed, as well as superb electronic control and low maintenance requirements. They are undoubtedly one of the most widely used motors in the DC motor family.
BLDC motors are highly efficient, capable of producing substantial torque over a large speed range. They are also characterized by permanent magnets that revolve around a fixed armature, which avoids the issue of connecting current to the armature. 

Figure 1. BLDC Motor, Yen-Shen Electric

BLDC Motor Structural Design 

In all BLDC motor designs, manufacturers aim to optimize the motor torque. Torque is the amount of rotational force generated by the motor during the operation. The key components of a BLDC motor include the rotor, magnets, and stator winding, all of which contribute to torque production. 

The rotor is the spinning component in a BLDC motor. A bearing is used to achieve smoother spinning. As with most brushless DC motors, the rotor has permanent magnets attached to it. The higher the number of pole pairs a magnet has, the more torque a brushless motor can produce given the same dissipated power. The role of the stator winding is to provide the power required to guide the magnetic field in the usable channel. Refer to the diagram below for the structural design of BLDC motors:

Figure 2. Structural Design of BLDC Motors

Types of BLDC Motors

There are two types of BLDC motors – inner rotor motor and outer rotor motor. While their working principle is the same, the difference lies in the design.

Figure 3. BLDC Motor Scheme, Inner and Outer Rotor Design

Inner Rotor Motor
In this design, the rotor is located in the center of the motor, surrounded by the stator winding. Since the rotor magnets do not insulate the heat inside in such a design, the heat is easily dispersed, which can produce a large amount of torque. 

Outer Rotor Motor
In this BLDC motor design, the rotor is located in the core of the motor, and surrounds the stator winding. Conversely, the magnets are able to retain the heat and prevent it from dissipating out of the motor. Such a design produces lower torque and operates at lower rate current.

How Do BLDC Motors Work?

What powers a DC motor has much to do with passing current to the rotor coils. So if DC motors typically use brushes to deliver current, how does a brushless motor transfer current to the rotor? It doesn’t. The brushless motors apply a remotely different principle to turn the rotor – by utilizing permanent magnets that rotate. The permanent magnets generate the magnetic fields through rotations, which then act on the coils on the rotor. Since the coils are stationary, there is no need for a commutator and brushes to make the rotor spin. To control the rotation, simply adjust the direction and magnitude of the current conveyed into the coils. Check out the video below to see how a BLDC motor operators:

(Copyright@Lesics, YouTube)

Advantages and Disadvantages

In a nutshell, BLDC motors are an efficiency powerhouse because of their ability to consistently control the rotation at maximum torque. See all advantages and some disadvantages outlined below: 

Advantages + 

  • Efficiency is enhanced because of the absence of brushes, which results in less energy loss due to friction.
  • The unique principle of supplying current, rather than voltage, makes BLDC motors a lot more efficient.
  • BLDC motors can operate at any speed under any environment and condition. 
  • BLDC motors make less noise.
  • Additional magnets can be retrofitted on the stator for more control.
  • BLDC motors have a long life and are easy to maintain because of the absence of brushes.
  • Due to the lack of a commutator, no ionizing sparks will be produced to cause electromagnetic interference. 
  • BLDC motors can generate large torque over a vast speed range.

Disadvantages –

  • BLDC motors are more expensive than their brushed counterparts. 
  • Although the outer ring design prevents the heat from dissipating from the motor, too much heat can weaken the magnets and damage the stator winding.

Applications of BLDC Motors

BLDC motors are widely used in many industries, especially industrial automation, aerospace, automotive, and medical industries.

Brushless motors are found in electric and hybrid vehicles. In the scooter sector, BLDC motors are much preferred as well because of their high efficiency. The motors are often built into the wheels of the vehicles. 

Brushless motors are used in a wide range of sectors in the aerospace industry, including satellites, gyroscopes, and aircraft on-board instruments. They are also very prevalent in the aircraft modeling sector. Model helicopters and drones often incorporate these motors.

BLDC motors are perfect for the high-speed production of surgical tools, from small dental hand tools to something as big as drills. They are also used in niche areas such as surgical robotics, bionics and exoskeleton systems, etc.

Industrial Automation & Robotics
BLDC motors are used in a range of industrial equipment such as pumps, conveyors, and assembly devices. They often are the key component in advanced robotic arms for highly automated production today. 

Other sectors in which brushless DC motors are used include barcode readers, camera, precision components, engraving, locks and more.

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