Brushed vs. Brushless Motors: The ultimate choice?

VD November 11 2021

From high-end steel rolling mills to everyday use machines, both brushed and brushless motors play a crucial role. 

If we take a deeper look at the origin of the whole 'brushed vs. brushless motors' fight, the mere base of such a comparison was the widespread use of these motors itself.  Brushed motors are quite popular, whereas brushless motors are gradually gaining momentum.

Their respective strengths and weaknesses vary greatly. Therefore the choice of the proper motor is highly dependent on several criteria, such as application type, desired torque, peak current rating, etc.

So if you have to choose between brushed or brushless motors for your application what should you do? Well, don't worry because in this article I will try to compare these two types of electric motors in order to help you with making up your mind. We will cover brushed vs. brushless speed control systems, brushes system faults, and tell about the advantages and disadvantages of both systems!

In this article, we will take a look at all the aspects associated with these motors that will affect your everyday work in the long term.

The impact of an armature

The most prominent feature that distinguishes a brushed motor from a brushless is the armature itself. 

When the DC source powers the armature, the already charged coil is pulled by the permanent magnet resting within the frame of the motor.

When we are talking about a brushed motor, the armature will be influenced by the motion of the commutator ring as well. As the commutator ring rotates, the connection will jump from one carbon brush to another, creating a stable torque effect with the DC power supply. 

Now, if we take a look at the brushed motors' rotating axis, we will see that it is fixed, unlike the brushless ones.

This means that all of the motor torque has to be developed by its coils and permanent magnets. Of course, this makes it more difficult for a brushed motor to operate at higher speeds. Now let's move on and inspect what brushes actually do!

The number one reason why electric motors fail: excessive arcing

When there is an arc between two contacts (brushes and commutator ring), current flows through those arcs rather than through the wire insulation as intended by design. Such currents cause welding between the materials which results in wire damage over time. As a consequence, such problems can lead to the breakdown of motor insulation and, eventually, create a short circuit. The path resistance is so low between the brushes and rotator that any metallic particles or conductive debris can form an electrical connection between them.

When welding occurs, it results in increased mechanical stress on the commutator ring and carbon brushes which causes malfunctions. Carbon brushes are subject to wear during normal operation, diminishing their ability to perform correctly over time. This can be solved by using special types of insulating materials for brushes but also by using brushless systems which eliminate this problem altogether!

Types of Brushless Motors

Nowadays there are three main types of brushless motors: AC induction motors (BLAC), permanent magnets (BLPM), and switched reluctance motors (BLSR).

The induction motor is, as the name suggests, an asynchronous machine that uses alternating current to produce a rotating magnetic field. In other words, this type of BLAC system does not have rotor bars inside the motor which results in lower cogging torque. It is great because it can be run from a DC supply as well as from AC supply by changing the input circuit. The permanent magnet BLAC system has short-circuited rotors with permanent magnets that do not rely on external power sources. This means that it cannot be started without a separate power source however there are several advantages: highest "starting" torque among all three types of brushless systems, simplicity and ease of use, independent of external power sources. Despite being simple, SR BLAC systems have the highest rotor inertia among all three types due to the reluctance torque produced by the stator created by commutator rings. It means that this type is suitable for high-inertia loads or use cases where speed must be rapidly adjusted.

AC induction motors are available in lots of different sizes and shapes which depends on their intended usage. BLPM motors are often used for aircraft because they feature amazing energy capabilities which makes them the perfect choice for that. Their main disadvantage however is not being able to use copper windings because that material tends to heat up too much when subjected to powerful magnetic fields but there is a solution:  water cooling which eliminates this problem and allows BLPM motors to be used for heavy-duty tasks. The only type of brushless motor which doesn't have such restrictions is SR BLAC which can use copper windings and doesn't require water cooling because it produces much less heat than AC induction motors.

Despite not being as famous as electric motors, brushless motors can be found in several areas of modern technology. They are used in CD/DVD drives for computers and other devices because they require a lot of power but at the same time don't have to be started very often. In addition, brushless motors are very often used in model aircraft due to high levels of torque at low speeds which make them perfect choice for small drones that must carry heavy payloads.

It should also be mentioned that there is one more type of BLAC system which aren't very famous among enthusiasts:  superconductor brushed linear motor but it has been designed mainly for scientific research and isn't available on the market just yet.

All three types of BLAC systems can be perfectly used for small drones which require a high level of torque but at the same time don't need to start very often. On the other hand, there are cases where the brushed motor is still a more suitable choice despite its disadvantages because it is more reliable and cheaper. For example, some self-balancing robots tend to favor using brushed motors due to simplicity/ease of use and availability on the market.

When it comes to choosing an electric motor for your drone you should always consider what you're going to do with it! Brushless systems are definitely superior in some areas but have certain limitations as well. If you're just a casual user who doesn't fly their drones every day, using a brushed motor might be a better idea because it is less expensive and easier to maintain. On the other hand, if you're looking for a high-end drone that features amazing torque at low speeds or has to carry heavy payloads frequently, a brushless system would definitely be the way to go.

Which option is the most efficient one?

It is tough to give a final answer about which motor type is more efficient, brushed vs. brushless motors. The whole design of a brushed motor is quite old as compared to the brushless motors.  With the constant use of commutator rings and carbon brushes, brushed motors become less efficient due to friction.

On the other hand, brushless motors do not have structures like a commutator ring or carbon brushes. Brushless motors are also way more incredible than brushed motors, even when working at total capacity. 

Plus, there is no loss of power to friction included in the case of brushless motors, making them a more efficient one.  Generally, brushless motors are more efficient but it's hard to say which is the best choice for you. If something goes wrong, that much power can lead to high damage or much trouble for you!

Brushless motors are definitely superior in some areas but have certain limitations as well - they need to use copper windings which make them expensive to build and not very reliable (heat issues). On the other hand, there are cases where a brushed motor is still a more suitable choice because it is cheaper and easier to maintain. It all depends on what your drone will be used for exactly.

Brushed vs. Brushless Motors: A battle of torque

The very basic and probably the only function of a motor is to generate torque. Torque, in general, is defined as the ability of a body to rotate around its axis when an external force is applied by someone. 

In the case of mechanics, this force is provided with the help of a motor.

When we talk about toque in the context of brushed vs. brushless motors and generating more of it, friction again comes into action. 

Brushed motors are more prone to friction which eventually diminishes their torque generating ability than a brushless motor.

Brushed Motors Advantages:

  • High torque

Because of their design, brushed motors are capable of generating much more torque as compared to brushless motors. It is because of the availability of commutator rings and carbon brushes in a brushed motors. 

The frictional resistance between these two components not only causes the loss of power but also generates additional heat thereby making the whole system less reliable due to heat issues. The best part about using brushed motors for your drone is that they are cheaper than brushless systems by a huge margin! Another advantage with this type of motor is that you don't have to worry about any complex wiring or controller, making them easier to use and providing ease of maintenance.

Brushed Motors Disadvantages:

  • Less Reliable

As compared to brushless motors, it is quite an issue with brushed motors because of their design and the usage of carbon brushes and commutator rings. Even though the system has been around for a while now, there are still a lot of problems that needs to be taken care of by users themselves or professionals. This makes them less reliable. Also, as these components become worn out over time, the performance becomes even worse making it difficult for you to keep flying your drone because of constant interruptions in flight! The only way out from this situation is that you replace those worn-out components but that would cost you too much money once again! All in all, using a brushed motor doesn't help much if you're looking for something more efficient.

Brushless Motors Advantages:

  • More Reliable

As compared to brushed motors, brushless motors are way more reliable because of their design. It is highly unlikely that you'll have problems with the functioning of brushless motors as it operates without any physical contact. As a result, there will be no wear and tear of components which ultimately leads to performance improvement over time! On top of that, much power means lesser chances of an error due to excessive heat production. However, keep in mind that there isn't anything much better than this type of motor even when it comes to generating torque but for now, brushless motors are the champions! With all the benefits they provide and almost zero downsides, using these motors is worth it.

Brushless Motors Disadvantages:

  • Expensive

Although they are more reliable than brushed motors, brushless motors are extremely expensive when compared to other types of motor systems. To get the most out of this system, you will have to buy a whole kit that includes ESC (Electronic Speed Controller) and battery eliminator circuit too! Although it may not be an issue for some people there are still others who don't want to invest so much in their DIY or RTF drones! Furthermore, brushless motors need to use copper windings which make them expensive to build and not very reliable (heat issues). On the other hand, there are cases brushed motor is still a more suitable choice than brushless motors.

Cost comparison

We can't conclude the battle of brushed vs. brushless motors without considering the cost associated with both these great motors. Brushed motors are older in design and are pretty reliable in use; that is why you can quickly get an effectively working brushed motor within a moderate price range.

Compared to brushed motors, brushless motors have a totally new design without commuter rings or carbon brushes. 

Plus, these motors are pretty popular when it comes to reducing friction and increasing efficiency. As a result, the price tag usually associated with a good quality brushless motor is higher than brushed models.

Even though the price of both these motors is pretty high but it totally depends on what you're looking for in your drone. If you are looking for raw power, a brushless motor with ESCs is definitely a more suitable choice than brushed ones! On the other hand, if you are looking for affordability and durability in your brushless quadcopters, using brushed motors can be a better option than any other choice out there!

Final note

Both brushed and brushless motors are supper effective in their respective functions according to the requirement. So, when it comes to declaring a clear winner of the brushed vs. brushless motors comparison, there is no clear winner as both the motors have their respective pros and cons.

Still, brushless motors are more like the evolution of brushed motors. It was designed specifically to cope with the overheating and excessive friction issue associated with brushed motors. Still, the concept of using brushless motors in high-end machinery is not that much in action, but considering brushless motors as the future of torque generating motors will not be wrong.