What is a Brushless Motor?

The brushless DC motor is composed of a motor body and a driver, and is a typical mechatronic product. Because the brushless DC motor runs in a self-controlled manner, it will not add a start winding to the rotor like a synchronous motor with heavy-duty starting under variable frequency speed regulation, and it will not produce oscillation and out-of-step when the load changes suddenly. The permanent magnets of small and medium capacity brushless DC motors now mostly use rare earth neodymium iron boron (Nd-Fe-B) materials with high magnetic energy levels. Therefore, the volume of the rare-earth permanent magnet brushless motor is smaller than that of the three-phase asynchronous motor of the same capacity by one frame size.

Electric motor

Brushless DC motors use semiconductor switching devices to achieve electronic commutation, that is, to replace traditional contact commutators and brushes with electronic switching devices. It has the advantages of high reliability, no commutation spark, and low mechanical noise. It is widely used in high-end recording bases, video recorders, electronic instruments and automated office equipment.

The brushless DC motor consists of a permanent magnet rotor, a multi-pole winding stator, and a position sensor. Position sensing changes the current of the stator windings along a certain sequence according to the change of the rotor position (that is, the position of the rotor poles relative to the stator winding is detected, and a position sensing signal is generated at a determined position. To control the power switch circuit, the winding current is switched according to a certain logic relationship). The working voltage of the stator winding is provided by an electronic switch circuit controlled by the position sensor output.

There are three types of position sensors: magnetic, photoelectric, and electromagnetic.

A brushless DC motor using a magnetic position sensor. The magnetic sensor (such as a Hall element, a magnetic diode, a magnetic dynatron, a magnetic resistor, or an application-specific integrated circuit) is mounted on the stator assembly. To detect changes in the magnetic field generated when the permanent magnet and rotor rotate.

A brushless DC motor using a photoelectric position sensor is equipped with a photoelectric sensor device at a certain position on a stator assembly, a light shielding plate is arranged on a rotor, and a light source is a light emitting diode or a small light bulb. When the rotor rotates, the light-sensitive components on the stator will generate pulse signals intermittently at a certain frequency due to the effect of the light shielding plate.

Brushless DC motors using electromagnetic position sensors are equipped with electromagnetic sensor components (such as coupling transformers, proximity switches, LC resonant circuits, etc.) on the stator assembly. When the position of the permanent magnet rotor changes, the electromagnetic effect will make the electromagnetic sensor Generate high-frequency modulated signals (the amplitude of which varies with rotor position). ^[1]

Structurally, brushless motors have similarities with brushed motors. They also have rotors and stators, but they are opposite to the structure of brushed motors. The rotors of brushed motors are coil windings, which are connected to the power output shaft. The stator is a permanent magnet. Steel; the rotor of the brushless motor is a permanent magnet magnetic steel, which is connected to the output shaft together with the casing, and the stator is a winding coil. The commutating brushes used by the brush motor to alternately change the electromagnetic field are removed, so it is called a brushless motor ( Brushless motor), then there is a problem now. Without the transformation of the electromagnetic field, how to make the brushless motor rotate?

In simple terms, by changing the alternating frequency and waveform of the current wave input to the stator coil of the brushless motor, a magnetic field rotating around the geometric axis of the motor is formed around the winding coil. This magnetic field drives the permanent magnetic steel on the rotor to rotate. The motor is turned on. The performance of the motor is related to the number of magnetic steel, the magnetic flux strength of the magnetic steel, and the input voltage of the motor. It also has a lot to do with the control performance of the brushless motor, because the input is direct current, and the current requires electronics. The governor will turn it into 3-phase AC power. It also needs to receive control signals from the remote control receiver to control the speed of the motor to meet the needs of the model. In general, the structure of the brushless motor is relatively simple. It is the brushless electronic governor that really determines its performance. A good electronic governor requires a single-chip microcomputer control program design, circuit design, and complex processing technology. The overall control, so the price is much higher than the brushed motor.

The comparison of brushless motor and brushed motor is as follows:

Brush motor disadvantages

(1) Large friction and large loss

Old model friends have encountered this problem when playing with a brush motor before, that is, after using the motor for a period of time, the motor needs to be turned on to clean up the carbon brush of the motor, which is time consuming and laborious, and the maintenance intensity is no less than a household cleaning.

(2) High fever and short life

Due to the structure of the brushed motor, the contact resistance between the brush and the commutator is very large, which causes the overall resistance of the motor to be large, and it is easy to generate heat. The permanent magnet is a thermal element. If the temperature is too high, the magnetic steel will be demagnetized To reduce the performance of the motor and affect the life of the brushed motor.

(3) Low efficiency and small output power

The heating problem of the brushed motor mentioned above is largely due to the fact that the current does work on the internal resistance of the motor, so the electrical energy is largely converted into thermal energy, so the output power of the brushed motor is not large and the efficiency is not high. ^[2]

Brushless motor advantages

(1) No brush and low interference

Brushless motors remove the brushes. The most direct change is that there are no electric sparks generated when the brushed motors are running. This greatly reduces the interference of electric sparks on remote radio equipment.

(2) Low noise and smooth operation

The brushless motor has no brushes, and the friction force is greatly reduced during operation, and the operation is smooth, and the noise will be much lower. This advantage is a huge support for the stability of the model operation.

(3) Long life and low maintenance cost

Without the brush, the wear of the brushless motor is mainly on the bearing. From a mechanical point of view, the brushless motor is almost a maintenance-free motor. When necessary, you only need to do some dust removal maintenance. The next comparison, we know where the advantages of brushless motors over brushed motors are, but everything is not absolute. Brushed motors have excellent low-speed torque performance and large torque. Performance characteristics such as brushless motors are irreplaceable, but In terms of the ease of use of brushless motors, with the decline in the cost of brushless controllers and the development and market competition of brushless technology at home and abroad, brushless power systems are developing and popularizing at a high speed, which has also greatly promoted The development of model movement.

Other differences

(1) Application:

Brushless motor: It is usually used on equipment with high control requirements and high speed, such as aircraft models, precision instruments, etc., which strictly control the speed of the motor and reach high speed.

Carbon brush motor: Usually brushed motors are used in power equipment, such as hair dryers, factory motors, household range hoods, etc. In addition, the speed of series motors can also reach very high, but due to the wear of carbon brushes, Life is not as good as brushless motors.

(2) Service life:

Brushless motor: Usually the service life is in the order of tens of thousands of hours, but the service life of brushless motors varies greatly due to different bearings.

Carbon brush motors: The continuous working life of brushed motors usually ranges from a few hundred to more than 1,000 hours. When the limit of use is reached, the carbon brushes need to be replaced, otherwise it is easy to cause bearing wear.

(3) Use effect:

Brushless motor: Usually digital frequency conversion control, strong controllability, can be easily realized from several revolutions per minute to tens of thousands of revolutions per minute.

Carbon brush motor: The old carbon brush motor generally works at a constant speed after startup, and speed regulation is not easy. Series-excited motors can also reach 20,000 rpm, but the service life will be short.

(4) Energy saving:

Relatively speaking, brushless motors controlled by frequency conversion technology will save a lot of energy than series-excited motors. The most typical ones are variable frequency air conditioners and refrigerators.

(5) Future maintenance:

Carbon brush motors need to be replaced with carbon brushes. If the brushes are not replaced in time, the motors will be damaged. Brushless motors have a long service life, which is usually more than 10 times that of brushed motors. However, if the motors are broken, they need to be replaced. However, daily maintenance is basically No need.

(6) The noise aspect has nothing to do with whether it is a brushed motor or not, it mainly depends on the cooperation between the bearing and the internal components of the motor.

(7) In addition to the parameters of the model brushless motor, in addition to the external dimensions (outer diameter, length, shaft diameter, etc.), weight, voltage range, no-load current, maximum current and other parameters, an important index K _V value is indispensable. This The value is a unique performance parameter of the brushless motor, and it is an important data to judge the performance characteristics of the brushless motor.