Updated
  
5
 
Jan
 
2021
Published
 
5
 
Dec
 
2019

Brushless motors insight

Brushless electric motors structure is simple and efficient, which gives them a huge advantage over brushed motors.
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DJI Mini 2 quadcopter design featuring out-runner motors

There are two (2) main types of electric motors in existence: mechanical brushed motors and electronic brushless electric motors. Other motor types exist for various niche industries, but their usage is limited. Electric motors work by utilising the natural phenomenon of electromagnetism. That is when an electric current passes through a conductive object it creates a magnetic field.

In order to make the magnetic field stronger, wires are used in extreme lengths and packed closely in the form of coils called motor windings. These wires are insulated to force electricity to move the longest distance possible, and are winded on top of a ferrous material (ex. iron) to amplify the electromagnetic field.

Electric motors usually utilise three (3) or more coils placed opposite to two (2) or more magnets. These magnets can be permanent magnets or electromagnets. In mechanical motors, the magnets are stationary while the coils rotate. In electronic motors, coils are stationary, while the magnets rotate. The rotating part is called the rotor.

Alpa Electro the first production electric aircraft
Alpa Electro the first production electric aircraft enabled by a brushless motor

Brushed motors (mechanical)

In mechanical electric motors where the coils are rotating, a mechanism called the commutator is used to transfer electricity into the coils while in motion. Each coil two ends is attached to different conductive contacts against a conductive brush. As such, when the rotor is rotating, the current still manage to flow into the coils. The mechanism of the commutator is different for each electric motor type.

Main Characteristics

° Commonly called AC or DC (brushed) motors

° Run at low RPM

° Use high voltage (V)

° Use low current (A)

° Work best with low ratio gear-sets

° Produces internal sparks

° Produce relatively high noise

° Require periodical maintenance

° Maximum efficiency ~80%


A set of carbon brushes for a power tool
Carbon brushes set for a power tool, Affiliate product page

AC motor

This motor type was the first to be invented by Galileo Ferraris and later perfected by Nikola Tesla in 1880s. Today it is commonly known as the AC motor, where AC stands for alternating current. The AC motor -although very old- is still the most commonly found in most industrial applications. This is mainly due to its seamless commutator design.

Photo of Nikola Tesla patent in 1888
Nikola Tesla patent featuring slip rings in 1888, U.S. Patent 381968

The AC motor commutator utilises something called slip rings, which is basically an array of conductive rings attached to its rotor shaft. Each coil is connected to two slip rings. As the alternating current (AC) changes its phases (positive to negative and vice versa) the magnetic field in each coil also changes its polarity. This allows the coils to move away from opposite magnets with the same polarity, and the motor moves.

For electricity to continuously be in touch with the slip rings, carbon brushes are used to maintain the connection. Unfortunately, this leads to a loss in efficiency and those brushes need to be replaced regularly to maintain the motor performance.


DC motor

Similar to the AC motor, the Direct Current (DC) motor relies on a mechanical mechanism to transfer current into the coils. The DC electric motor invention is mostly attributed to Michael Faraday from the United Kingdom (UK) in the 1820s. Faraday was able to demonstrate a working prototype of the DC motor in 1821.

Unlike the AC motor, the DC motor uses only one-phase DC electricity. This makes it reliant on the rotation of the rotor to alternate the current phases. Since most machinery and appliances rely on AC outlets, using a DC motor usually requires an inverter, which is expensive and bulky. For these reasons, DC motors are usually reserved for lower power applications and are currently being replaced by the modern electric motor.

Photo of a small cylindrical DC motor showing its model number and input voltage 12 volts.
JYCRS390H 6-12 volts DC motor, Affiliate product page

Brushless motors (electronic)

The induction motor of the 1880s is considered the original concept behind the modern motor. However, the actual development of electronically-controlled electric motors only started in the 1960s, after the MOSFET transistor was invented in 1959 by Mohamed M. Atalla in New York City. Today these modern motors are known as Brushless or BLDC motors, short for Brushless Direct Current motors. This is due to the lack of brushes, as they rely on stationary coils, making them commutator-free.

The structure of these motors is simple and efficient, as they rely on electronics for control. This electronic control unit is known as an electronic speed controller or ESC. Some may refer to the control unit as an inverter, as it inverts direct current into alternating current. However, ESCs are usually much smaller than traditional inverters. They also operate more efficiently as the frequency can be controlled and fine-tuned in real-time for maximum performance. There are two main types of brushless motors: in-runner motors and out-runner motors. One has the rotor on the inside, while the other has an outer rotor.

Main Characteristics

° Commonly called brushless motors

° Run at high RPM

° Use low voltage (V)

° Use high current (A)

° Work best with high ratio gear-sets

° Does not produce sparks

° Produce relatively low noise

° Run maintenance-free

° Maximum efficiency ~90%

In-Runner motor

As the name suggests, in-runner motors have the rotor rotating inside with its shaft extended through a hole in the motor housing. Thus, motor windings are lined up along the hosing inner wall. This makes them perfect for applications that require power at lower speeds. Especially when the surrounding environment is harsh, as the motor can be totally enclosed and shielded from the elements.

1600W in-runner brushless motor
1600W in-runner brushless motor, Affiliate product page

Out-Runner motor

Out-runner motors have the housing itself rotating on the outside with the permanent magnets, while the coils are grouped on a stationary base. The moment from the bigger diameter rotating element makes these motors run at astronomical speeds easily reaching speeds of 50,000 rpm and beyond. They are usually lighter too, so since they feature an open housing and are most common in-flight applications, e.g. quadcopters.

DJI Mini 2 design featuring out-runner motors
DJI Mini 2 design featuring out-runner motors, Affiliate product page
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Brushless motors advantages

Over the years, modern electric motors, also known as brushless motors, have increased in popularity. It has allowed manufacturers to produce and consumers to enjoy what is known as modern electric devices. Today, you will find them in a lot of electronic devices, such as cordless power tools, that are used in a variety of home and industrial applications. It seems that many manufacturers of electronic devices are jumping on the brushless motor bandwagon. So, what is a brushless motor, and what advantages does it offer?

To understand what a brushless motor is, we have to take a brief look at what they evolved from, which is brushed motors. Basically, a brushed motor contains carbon brushes that transfer current coming from a power source (battery or power outlet) to commutator contacts located on the motor’s shaft. Over the past century, they were used is almost everything from power tools to fridges and fans, and even as car generators. Now, the shaft contains a spinning armature/rotor inside of it and two permanently installed magnets on the outside. When the electric current reaches the armature, the electromagnet inside of it generates a magnetic field that repels the magnets, causing the motor to spin.

As the motor spins, so do the commutator contacts, and the brushes come in constant contact with them as they spin. This leads to several undesirable outcomes. For one, it means that the brushes will eventually wear out. Secondly, this produces a lot of electrical noise and sparks. Thirdly, the sparks cause some energy to dissipate. Since there are no brushes in brushless mortars, they are much more efficient. There is no wearing of brushes to worry about, meaning brushless motors last longer. Noise and sparks are also significantly reduced. Thirdly, fewer sparks mean less energy dissipation, meaning brushless mortars require less power than their brushed counterparts to spin.

A brushless motor removes the carbon brushes and the commutator contacts from this setup. At this point, you might be asking yourself how power even reaches the armature when there are no brushes and commutator contacts to facilitate the transfer of current. Well, that is where some sort of circuit board is used to control the power that is supplied to the armature. The power is controlled using sensors located on the circuit board. For this setup to work, the armature is moved to the outside of the shaft while the magnets are placed on the inside. The removal of the brushes and commutator contacts coupled with the addition of a circuit board is where the advantages of the brushless motor lie.

Affordable

Perhaps this is one area where brushed motors have a slight advantage – the fact that they cost less. Because of their control complexity, brushless motors have higher initial costs, but they make up for this with improved efficiency and durability (no brushes to wear down).

As you can see, brushless motors have ushered in a new generation of modern electric devices that are compact in size and offer better performance. Compared to conventional devices with brushed motors, the praise modern electric devices are getting is well deserved, although they cost more. Modern electric devices are taking over, and many manufactures, as well as consumers, have wised up to their benefits and are not looking back.

Smart

The circuitry in the brushless motors that control the current makes brushless motors “smart.” Regardless of what you are doing, brushed motors will transfer the same amount of current to the motor all the time (unless there is some switch that you can use to manually control this). Brushless motors, on the other hand, have circuitry that can detect how much current the motor needs depending on the task you are doing at the moment.

Perhaps an example will best illustrate how this is a huge advantage. Suppose you are in the process of drilling some wood. Depending on how thick the wood is, a brushless motor will detect how much current should be transferred to the motor based on how much resistance the drill is facing. This has the advantage of making work more efficient. If the drill is cordless, less battery power will be used for the job compared to a brushed motor, which will use the same battery power no matter the job.

Now that you know the advantages of brushed motors, you can see that their popularity is well deserved. They are a drastic improvement over their brushed counterparts and that is what makes them a better alternative to brushed mortars. That is why many companies are using them in their electronics and many consumers are buying them.

Perform

When contrasted with brushed motors, brushless motors are smaller in size. This means they allow manufacturers to make compact devices without sacrificing speed and performance. This means an electric saw made from a brushed motor would be bigger in size compared to one made with a brushless motor.

As you can imagine, a compact electric saw would be easier to handle and take less power (not to mention it would be much more powerful due to the brushless motor). Not only that, brushless motors allow manufacturers to produce mini versions of popular consumer gadgets as well.

Due to their brushless motors, modern electric devices are more efficient than conventional devices. Brushed motors require brushes, commutators and connections to deliver power to the rotor, the component on the motor shaft that causes the motor to spin, while brushless motors get their power delivered directly to the rotor using some type of control circuitry, eliminating the need for brushes.

The first boost in performance comes from the lack of brushes. Brushes are what deliver the current to the commutator contacts of the rotor. When this happens, some of the current is lost to heat. Since the power goes straight to the rotor in a brushless motor, no power is lost, making it more efficient than brushed motors. This also means it takes less juice to power a modern electric device compared to a conventional device.

The control circuitry found on brushless motors gives modern electric devices the ability to automatically control speed/torque. This is thanks to the sensors that are located on the control circuit, allowing it to detect the amount of stress the electric device is going through. If it is under a lot of stress, the motor will spin furiously, and when there is less stress, the motor of the modern electric will spin less.

Versatile

The global market for brushless direct current motors (BLDC) is witnessing growth, accelerated by electric vehicle (EV) adoption, manufacturing robotics evolution, and modern household appliances. Among the most valuable advantages of brushless motors, are their high performance, control-ability, and low maintenance cost. Since these motors do not depend on brushed contacts, they are dust-proof and mostly require no maintenance for multiple years of operation. Moreover, popular manufacturing uses such motion control and positioning system also involve these motors.

Today most of the electric motors adapted in EVs are brushless DC motors. Compared to the conventional brushed motors with average efficiency under 80%, brushless motors can reach up to 90% efficiency with a good design. Meanwhile, they are safer since sparking caused by dust within brushes can be avoided, thus reducing risks of catching fire and system failure. Brushless motors are most common among smaller vehicles such as electric bikes, electric motorcycles.

Light-weight motors enable consumers to easily move or carry their vehicles around. Moreover, brushless motors are deployed in hybrid electric and plug-in hybrid vehicles depending on their use. Advanced vehicle features may include adjustable mirrors, automotive sunroofs, etc. Power motors for these feature sets are now gradually changed from brushed ones to brushless.

Medical applications favour a brushless motor for its quietness, safety, and high control-ability. For instance, a blower fan used to treat sleep apnoea (temporary cessation of breathing while sleeping) needs to adjust its speed per the patient’s condition. In this case, a brushless motor can function smoothly at different speeds without minimum threshold, and with explicit low noise.

Good robotic service and robot design require precision and faster responding time, and that is why BLDC motors can out-stand their counterparts. Brushless motor mechanism enables itself to fast reach a higher peak current, therefore providing better performance in versatile operations. Brushless motors can also offer reliable service when going high up to space—utilised to power an oxygen transferring system on NASA aerospace; and too deep in the ocean—underwater drones. These are all owing to the technology's excellent resistant performance under extreme environmental conditions.

Brushless motors bring such advantages to manufacturers, industrial segments and consumers, while the higher expenditures make it seem less appealing, the market price of some permanent magnet materials continuously experienced a downward fluctuating trend.

Clean

The debate over burning fossil fuels is something that gets more heated every year. The main source of contestation is that this type of fuel is non-renewable, meaning one day we will eventually run out. But with so many devices using an internal combustion engine (combustion engine), which need fossil fuels to run, is there an alternative that uses a renewable source of energy? The answer is yes.

The brushless motor is gaining popularity as an alternative to the combustion engine. The main selling point is that they use a renewable source of energy: electricity. While combustion engines burn up fossil fuels to create heat, which they then use to make mechanical energy, brushless motors use electricity to the same effect. Other than that, can we also say they are better in other areas than combustion engines?

Brushless motors are more practical compared to combustion engines which have a lot of moving parts, usually hundreds of parts, and they require supporting systems, such as a cooling system (radiator), lubrication system and gear transmission system. This means manufacturing them is complicated and hard. On the other hand, brushless motors have a couple of moving parts and can operate with none of these supporting systems. This means a vehicle made from brushless motors (electric vehicles) are easier to manufacture.

Since brushless motors are less complex than combustion engines, maintaining them is much easier as well. Due to the sheer amount of moving parts in combustion engines, these devices are much more vulnerable to faults, hence they require more maintenance compared to brushless motors. This means electric vehicles are easier and cheaper to maintain.

Although refuelling of combustion engines’ tanks is usually much faster, since all one does is fill up the tank of the vehicle. However, these days, modern vehicles can travel up to 644 km (400 miles) on a full tank of gas. This is significantly better than electric cars, which have been known to go up to 322 km (200 miles) before they need to be recharged.

Brushless motors are also much better for the environment than combustion engines since they cause less pollution. This makes them better for companies that are trying to spearhead the green initiative. In fact, brushless motors account for 15% of the pollution because lithium-ion batteries are not being disposed of properly. On the other hand, the emission of greenhouse gasses from vehicles is responsible for 50-90% of air pollution in urban areas.

Due to the internal combustion taking place and the firing of the cylinder’s pistons, combustion engine’s produce a lot of noise. This is the sound of hundreds of mechanical parts rubbing against each other. With brushless motors, the highest noise that can be heard is the whining sound that the pulse width modulation (PWM) driver, located on the control circuitry of the motor, makes as it switches frequencies.

While each device has its advantages and disadvantages, brushless motors are the future while internal combustion engines will become less sustainable in the long run as we deplete fossils fuels. This is a big point to consider for companies still manufacturing devices that use combustion engines. Rather than concentrate on a dying technology, it is better to switch to brushless motors and work towards making them more efficient.

Brushless motors future

The inherent durability aspect of being commutator-free makes electronic brushless motors perfect for future applications, where reliability is increasingly the top priority.  As such as early as the invention of the floppy drive, brushless motors were the go-to motor of choice. Today, almost all computer fans utilise brushless motors too.

Tesla Model S skateboard structure featuring two brushless motors.
Tesla Model S skateboard featuring two brushless motors

Today, electronic motors have entered into every industry and continue to enter new applications every year. The most notable application where electronic motors are in use today is in electric vehicles (EVs) from slim compact scooters to sports cars and electric aircrafts.


The story is still developing too as these motors get introduced into more applications. So next time you are looking for an electric machine, look for ones with these new motors to get the best performance.

Parts of this insight were first published 
as early as 
December 2019
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Prince Hassan

20+ years of experience in products research and development (R&D) and expert in design for manufacturing (DFM). Founder and CEO of DegreeSign.
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