Brushless electric motors are used in medical equipment, aircraft modeling, pipe shut-off drives of oil pipelines, as well as in many other industries. But they have their drawbacks, features, and advantages, which sometimes play a key role in the design of various devices. Be that as it may, such electric motors occupy a relatively small niche when compared with asynchronous AC machines.
Features of electric motors
One of the reasons why designers are interested in brushless motors is the need for high-speed motors with small dimensions. Moreover, these engines have very precise positioning. The design has a movable rotor and a fixed stator. On the rotor there is one permanent magnet or several, arranged in a certain sequence. On the stator there are coils that createmagnetic field.
One more feature should be noted - brushless motors can have an anchor located both inside and on the outside. Therefore, the two types of construction may have specific applications in different areas. When the armature is located inside, it turns out to achieve a very high rotation speed, so such motors work very well in the design of cooling systems. If an external rotor drive is installed, very precise positioning can be achieved, as well as high overload resistance. Very often, such motors are used in robotics, medical equipment, in machine tools with frequency program control.
How motors work
In order to drive the rotor of a brushless DC motor, you must use a special microcontroller. It cannot be started in the same way as a synchronous or asynchronous machine. With the help of a microcontroller, it turns out to turn on the motor windings so that the direction of the magnetic field vectors on the stator and armature are orthogonal.
In other words, with the help of a driver, it is possible to regulate the torque that acts on the rotor of a brushless motor. To move the armature, it is necessary to carry out the correct switching in the stator windings. Unfortunately, it is not possible to provide smooth rotation control. However, it can be increased very quickly.motor rotor speed.
Differences between brushed and brushless motors
The main difference is that the brushless motors for the models do not have a winding on the rotor. In the case of collector electric motors, there are windings on their rotors. But permanent magnets are installed on the stationary part of the engine. In addition, a collector of a special design is installed on the rotor, to which graphite brushes are connected. With their help, voltage is applied to the rotor winding. The principle of operation of a brushless motor is also significantly different.
How the collector machine works
To start the collector motor, you will need to apply voltage to the field winding, which is located directly on the armature. In this case, a constant magnetic field is formed, which interacts with the magnets on the stator, as a result of which the armature and the collector fixed on it rotate. In this case, power is supplied to the next winding, the cycle is repeated.
The speed of rotation of the rotor depends directly on how intense the magnetic field is, and the last characteristic depends directly on the magnitude of the voltage. Therefore, in order to increase or decrease the speed, it is necessary to change the supply voltage.
To implement the reverse, you only need to change the polarity of the motor connection. For such control, it is not necessary to use special microcontrollers,you can change the rotational speed using a conventional variable resistor.
Features of brushless machines
But the control of a brushless motor is impossible without the use of special controllers. Based on this, we can conclude that motors of this type cannot be used as a generator. For efficient control, the position of the rotor can be monitored using multiple Hall sensors. With the help of such simple devices, it is possible to significantly improve performance, but the cost of the electric motor will increase several times.
Starting brushless motors
It makes no sense to make microcontrollers on your own, a much better option would be to buy ready-made, albeit Chinese. But you must adhere to the following recommendations when choosing:
- Remember the maximum allowable current. This parameter will be useful for various types of drive operation. The characteristic is often indicated by manufacturers directly in the model name. Very rarely, values are indicated that are typical for peak modes, in which the microcontroller cannot operate for a long time.
- For continuous operation, the maximum supply voltage must also be taken into account.
- Be sure to consider the resistance of all internal microcontroller circuits.
- Be sure to take into account the maximum number of revolutions that is typical for the operation of this microcontroller. Please note that he is notwill be able to increase the maximum speed, since the limitation is made at the software level.
- Cheap models of microcontroller devices have a frequency of generated pulses in the range of 7…8 kHz. Expensive copies can be reprogrammed, and this parameter increases by 2-4 times.
Try to select microcontrollers in all respects, as they affect the power that the electric motor can develop.
How it is managed
The electronic control unit allows switching the drive windings. To determine the moment of switching using the driver, the position of the rotor is monitored by the Hall sensor installed on the drive.
If there are no such devices, it is necessary to read the reverse voltage. It is generated in the stator coils that are not connected at the moment. The controller is a hardware-software complex, it allows you to track all changes and set the switching order as accurately as possible.
Three-phase brushless motors
A lot of brushless electric motors for model aircraft are powered by direct current. But there are also three-phase instances in which converters are installed. They allow you to make three-phase pulses from a constant voltage.
Work is as follows:
- Coil "A" receives pulses frompositive value. On coil "B" - with a negative value. As a result of this, the anchor will begin to move. The sensors fix the displacement and a signal is sent to the controller for the next switching.
- Coil "A" is switched off, while a positive pulse is sent to the "C" winding. Switching winding "B" does not change.
- Positive impulse gets to the coil "C", and the negative one goes to "A".
- Then pair "A" and "B" come into play. Positive and negative values of pulses are fed to them, respectively.
- Then the positive pulse again goes to the "B" coil, and the negative one to the "C".
- At the last stage, coil "A" is turned on, which receives a positive pulse, and a negative one goes to C.
And after that the whole cycle repeats.
Benefits of using
It is difficult to make a brushless electric motor with your own hands, and it is almost impossible to implement microcontroller control. Therefore, it is best to use ready-made industrial designs. But be sure to consider the benefits that the drive gets when using brushless motors:
- Significantly longer resource than collector machines.
- High level of efficiency.
- More powerful than brushed motors.
- Rotation speed picks up much faster.
- No sparks during operation, so they can be used in environments with a high fire hazard.
- Very easy drive operation.
- No need for additional cooling components during operation.
Among the shortcomings, one can single out a very high cost, if we also take into account the price of the controller. Even for a short time to turn on such an electric motor to check the performance will not work. In addition, repairing such motors is much more difficult due to their design features.
