Why is brushless better

In applications like this, the DC voltage is simply switched on and off to make the motor run or stop. This is typical in low cost applications like motorized toys. If reversal is needed, it can be accomplished by using a double pole switch.

This allows the voltage to be applied to the motor in either polarity, which makes the motor rotate in opposite directions. The motor speed or torque can be controlled by pulse width modulating one of the switches. Brushless DC Motors image by maxon group.

Brushless DC motors operate on the same principle of magnetic attraction and repulsion as brush motors, but they are constructed somewhat differently. Instead of a mechanical commutator and brushes, the magnetic field of the stator is rotated by using electronic commutation.

This requires the use of active control electronics. In a brushless motor, the rotor has permanent magnets affixed to it, and the stator has windings. The number of windings used in a brushless motor is called the number of phases.

Though brushless motors can be constructed with different numbers of phases, three phase brushless motors are the most common. An exception is small cooling fans that may use only one or two phases. In either case, there are three wires connecting to the motor, and the drive technique and waveform is identical. With three phases, motors can be constructed with different magnetic configurations, called poles. The simplest 3-phase motors have two poles: the rotor has only one pair of magnetic poles, one North and one South.

Motors can also be built with more poles, which requires more magnetic sections in the rotor, and more windings in the stator. Higher pole counts can provide higher performance, though very high speeds are better accomplished with lower pole counts. To drive a three phase brushless motor, each of the three phases needs to be able to be driven to either the input supply voltage or ground. There are a number of drive techniques that can be employed for three phase brushless motors.

The simplest is called trapezoidal, block, or degree commutation. Trapezoidal commutation is somewhat similar to the commutation method used in a DC brush motor. In this scheme, at any given time, one of the three phases is connected to ground, one is left open, and the other is driven to the supply voltage. If speed or torque control is needed, usually the phase connected to the supply is pulse width modulated.

Since the phases are switched abruptly at each commutation point, while the rotor rotation is constant, there is some variation of torque called torque ripple as the motor rotates. For higher performance, other commutation methods can be used. Sine, or degree, commutation drives current thorough all three motor phases all of the time. The drive electronics generates a sinusoidal current though each phase, each shifted degrees from the other. This drive technique minimizes torque ripple, as well as acoustic noise and vibration, and is often used for high performance or high efficiency drives.

To properly rotate the field, the control electronics need to know the physical position of the magnets on the rotor relative to the stator. Often, the position information is obtained using Hall sensors that are mounted to the stator. As the magnetic rotor turns, the Hall sensors pick up the magnetic field of the rotor. This information is used by the drive electronics to pass current through the stator windings in a sequence that causes the rotor to spin.

Using three Hall sensors, trapezoidal commutation can be implemented with simple combinational logic, so no sophisticated control electronics are needed. Other commutation methods, like sine commutation, require a bit more sophisticated control electronics, and usually employ a microcontroller. In addition to providing position feedback using Hall sensors, there are various methods that can be used to determine the rotor position without sensors.

The simplest is to monitor the back EMF on an undriven phase to sense the magnetic field relative to the stator. A more sophisticated control algorithm, called Field Oriented Control or FOC, calculates the position based on rotor currents and other parameters. FOC typically requires a fairly powerful processor, as there are many calculations that have to be performed very quickly.

This, of course, is costlier than a simple trapezoidal control method. Depending on your application, there are reasons why you might choose to use a brushless motor over a brushed motor. While the technology isn't exactly new, it has gained traction in recent years due to some high-profile releases by Makita, Milwaukee, DeWalt, and others.

We love fixing stuff. Let's do it together. Makita, however, was the first company to use them in power tools. Manufacturers claim that brushless tools have added performance and durability and that they're smarter than the average tool. So what exactly is the technology behind these new motors? A traditional brushed motor is made up of four basic parts: carbon brushes, a ring of magnets, an armature, and a commutator.

The magnets and brushes are stationary, while the armature and commutator rotate together on the motor shaft within the magnets. When the motor is energized, a charge travels from the battery, through the brushes, and into the commutator. The brushes are spring-loaded to maintain physical contact with the commutator. The commutator then passes the charge on to the armature, which is made up of copper windings they look like bundles of copper wire.

The windings are magnetized by the charge and push against the stationary ring of magnets that surround it, forcing the armature assembly to spin. The spin doesn't stop until the charge from the battery stops. A brushless motor loses the brushes and the commutator. And the locations of the magnets and windings are reversed: The magnets are on the conventional motor shaft and the copper windings of the armature are fixed and surround the shaft.

Since like charges oppose each other, this pushes the permanent magnet. Now the rotor is moving thanks to a pull and a push. The permanent magnets are moving in this case, so now they are my running partner and me. Instead, we know that I want the Boston creme doughnut and my partner wants the smoothie. This is what drives the cost of brushless motors up. Brushless motors offer several advantages over brushed motors thanks to the design. Much of it has to do with the loss of brushes and commutator.

Since the brush is required to be in contact with the commutator to deliver a charge, it also causes friction. Friction reduces the speed that can be achieved along with building up heat. Conversely, if you want to maintain the speed, it will take more energy from your legs. This means that, compared to brushed motors, brushless motors run cooler. That gives them more efficiency, so they convert more electricity into power.

Carbon brushes also wear down over time. In order to keep the tool running, the brushes have to be replaced once in a while. That leads to the opportunity for lighter weight and a more compact size. There seems to be a misconception around brushless motors and torque. For example, the first Milwaukee M18 FUEL hammer drill had less real-world torque than the brushed model that preceded it.

Eventually, however, manufacturers realized something very critical. The electronics used in brushless motors can supply those motors with more power when needed. Because brushless motors now utilize advanced electronic controls, they can sense when they begin to slow down under load. So long as the battery and motor are within temperature specs, the brushless motor electronics can ask for, and receive, more current from the battery pack.

This lets tools like brushless drills and saws maintain more speed under load. This makes them faster. Often much faster. Commutation—varying the polarity of the charge—starts the brushless motor and keeps it turning. Next, you need to control both speed and torque.

Varying the voltage to the stator of a BLDC motor controls the speed. Modulating the voltage at higher frequencies lets you control the motor speed to an even greater degree. Of course, this introduces the key need: motor monitoring and sensors. Hall effect sensors provide an inexpensive way to detect the position of the rotor.

They can also detect speed by timing when and how often the sensors switch. The combination of these benefits has another effect—a longer life. While the warranty is typically the same for brushed vs brushless motors and tools within a brand, you can expect to get a longer life out of the brushless models. This can often be years beyond the warranty. Remember what I said about the electronic controller essentially building a computer in your tool?

The brushless motor is also responsible for the breakthrough of smart tools hitting the industry. On the clock, Kenny dives deep to discover the practical limits and comparative differences for all kinds of tools. Off the clock, his faith and love for his family are his top priorities, and you'll typically find him in the kitchen, on his bike he's an Ironman , or taking folks out for a day of fishing on Tampa Bay.

As always, you can grab discounts on batteries and tool combo kits, but even individual tools show dramatic savings for those looking to expand the […].