For several years, we have been seeing brushless motors begin to dominate the cordless tool drive in the professional tool industry. This is great, but what’s the big deal? Is it really important as long as I can drive that wood screw? um, yes. There are significant differences and effects when dealing with brushed motors and brushless motors.
Before we delve into the two-foot brush and brushless motors, let us first understand the basic knowledge of the actual working principle of DC motors. When it comes to driving motors, it’s all related to magnets. Oppositely charged magnets attract each other. The basic idea of a DC motor is to keep the opposite electric charge of the rotating part (rotor) attracted to the immovable magnet (stator) in front of it, thereby continuously pulling forward. It’s a bit like putting a Boston Butter Donut on a stick in front of me when I run-I will keep trying to grab it!
The question is how to keep the donuts moving. There is no easy way to do it. It starts with a set of permanent magnets (permanent magnets). A set of electromagnets changes charge (reversing polarity) as they rotate, so there is always a permanent magnet with the opposite charge that can move. In addition, the similar charge experienced by the electromagnetic coil as it changes will push the coil away. When we look at brushed motors and brushless motors, how the electromagnet changes polarity is the key.
In a brushed motor, there are four basic components: permanent magnets, armatures, commutating rings and brushes. The permanent magnet constitutes the exterior of the mechanism and does not move (stator). One is positively charged and the other is negatively charged, creating a permanent magnetic field.
The armature is a coil or a series of coils that become an electromagnet when energized. This is also the rotating part (rotor), usually made of copper, but aluminum can also be used.
The commutator ring is fixed to the armature coil in two (2-pole configuration), four (4-pole configuration) or more components. They rotate with the armature. Finally, the carbon brushes remain in place and transfer the charge to each commutator.
Once the armature is energized, the charged coil will be pulled towards the oppositely charged permanent magnet. When the commutator ring above it also rotates, it moves from the connection of one carbon brush to the next. When it reaches the next brush, it will receive a polarity reversal and is now attracted by another permanent magnet while being repelled by the same kind of electric charge. Tangibly, when the commutator reaches the negative brush, it is now attracted by the positive permanent magnet. The commutator arrives in time to form a connection with the positive electrode brush and follow to the negative permanent magnet. The brushes are in pairs, so the positive coil will pull toward the negative magnet, and the negative coil will pull toward the positive magnet at the same time.
It’s like I am an armature coil chasing a Boston Butter Donut. I got close, but then changed my mind and pursued a healthier smoothie (my polarity or desire changed). After all, donuts are rich in calories and fat. Now I am chasing smoothies while being pushed away from Boston cream. When I got there, I realized that donuts are much better than smoothies. As long as I pull the trigger, every time I get to the next brush, I will change my mind and at the same time chase the objects I like in a frantic circle. It is the ultimate application for ADHD. In addition, there are two of us there, so Boston Butter Donuts and Smoothies are always chased enthusiastically by one of us, but indecisive.
In a brushless motor, you lose the commutator and brushes and gain an electronic controller. The permanent magnet now acts as a rotor and rotates inside, while the stator is now composed of an external fixed electromagnetic coil. The controller supplies power to each coil based on the charge required to attract the permanent magnet.
In addition to moving charges electronically, the controller can also provide similar charges to counter permanent magnets. Since the charges of the same kind are opposite to each other, this pushes the permanent magnet. Now the rotor moves due to the pulling and pushing forces.
In this case, the permanent magnets are moving, so now they are my running partner and me. We no longer change the idea of what we want. Instead, we knew that I wanted Boston Butter Donuts, and my partner wanted smoothies.
Electronic controllers allow our respective breakfast pleasures to move in front of us, and we have been pursuing the same things all the time. The controller also puts things we don’t want behind to provide push.
Brushed DC motors are relatively simple and cheap to manufacture parts (although copper has not become cheaper). Since a brushless motor requires an electronic communicator, you are actually starting to build a computer in a cordless tool. This is the reason for pushing up the cost of brushless motors.
Due to design reasons, brushless motors have many advantages over brushed motors. Most of them are related to the loss of brushes and commutators. Since the brush needs to be in contact with the commutator to transfer the charge, it also causes friction. Friction reduces the achievable speed and at the same time generates heat. It’s like riding a bicycle with light brakes. If your legs use the same force, your speed will slow down. Conversely, if you want to maintain speed, you need to get more energy from your legs. You will also heat the rims due to frictional heat. This means that, compared with brushed motors, brushless motors run at a lower temperature. This gives them higher efficiency, so they convert more electrical energy into electrical energy.
Carbon brushes will also wear out over time. This is what causes sparks inside some tools. In order to keep the tool running, the brush must be replaced from time to time. Brushless motors do not require this kind of maintenance.
Although brushless motors require electronic controllers, the rotor/stator combination is more compact. This leads to opportunities for lighter weight and more compact size. This is why we see many tools like Makita XDT16 impact driver with ultra-compact design and powerful power.
There seems to be a misunderstanding about brushless motors and torque. Brushed or brushless motor design itself does not really indicate the magnitude of torque. For example, the actual torque of the first Milwaukee M18 fuel hammer drill was smaller than the previous brushed model.
However, in the end the manufacturer realized some very critical things. The electronics used in brushless motors can provide more power to these motors when needed.
Since brushless motors now use advanced electronic control, they can sense when they start to decelerate under load. As long as the battery and motor are within the temperature specification range, the brushless motor electronics can request and receive more current from the battery pack. This allows tools such as brushless drills and saws to maintain higher speeds under load. This makes them faster. It is usually much faster. Some examples of this include Milwaukee RedLink Plus, Makita LXT Advantage and DeWalt Perform and Protect.
These technologies seamlessly integrate the tool’s motors, batteries, and electronics into a cohesive system to achieve optimal performance and runtime.
Commutation—change the polarity of the charge—start the brushless motor and keep it rotating. Next, you need to control speed and torque. The speed can be controlled by changing the voltage of the BLDC motor stator. Modulating the voltage at a higher frequency allows you to control the motor speed to a greater degree.
In order to control the torque, when the torque load of the motor rises above a certain level, you can reduce the stator voltage. Of course, this introduces key requirements: motor monitoring and sensors.
Hall-effect sensors provide an inexpensive way to detect the position of the rotor. They can also detect the speed by the time and frequency of the timing sensor switching.
Editor’s note: Check out our What is a sensorless brushless motor article to learn how advanced BLDC motor technology changes power tools.
The combination of these benefits has another effect-a longer life span. Although the warranty for brushed and brushless motors (and tools) within the brand is usually the same, you can expect a longer life for the brushless models. This can usually be several years beyond the warranty period.
Remember when I said that electronic controllers are essentially building computers in your tools? Brushless motors are also the breakthrough point for smart tools to impact the industry. Without the reliance of brushless motors on electronic communication, Milwaukee’s one-button technology would not work.
On the clock, Kenny deeply explores the practical limitations of various tools and compares the differences. After get off work, his faith and love for his family is his top priority. You will usually be in the kitchen, ride a bicycle (he is a triathlon) or take people out for a day fishing in Tampa Bay.
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Thanks for the explanation. This is something I have been wondering for a long time, seeing that most people are in favor of brushless (at least used as an argument for more expensive power tools and drones).
I want to know: Does the controller also sense the speed? Doesn’t it have to be done to synchronize? Does it have Hall elements that sense (rotate) magnets?
Not all brushless motors are better than all brushed motors. I want to see how the battery life of Gen 5X compares to its predecessor X4 under moderate to heavy loads. In any case, brushes are almost never a life-limiting factor. The original motor speed of cordless tools is approximately 20,000 to 25,000. And through the lubricated planetary gear set, the reduction is about 12:1 in the high gear and about 48:1 in the low gear. The trigger mechanism and motor rotor bearings that support the 25,000RPM rotor in the dusty air stream are usually weak points
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Post time: Aug-31-2021