Brushless motors are used in medical technology, aircraft modeling, pipe-gate drives of oil pipelines, as well as in many other industries. But they have their drawbacks, features, as well as 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 specifically in brushless motors is the need for high-speed motors with small sizes. Moreover, these engines have very accurate positioning. The design has a movable rotor and a fixed stator. There is one permanent magnet or several located in a certain sequence on the rotor. On the stator, there are coils that create a magnetic field.
One more feature should be noted - brushless motors can have an anchor located both inside and on the outside. Therefore, two types of construction can have specific applications in various fields. With the location of the anchor inside it turns out to achieve a very high speed of rotation, therefore, such motors work very well in the design of cooling systems. In that case, if the drive is installed with the external location of the rotor, it is possible to achieve very accurate positioning, as well as high resistance to overloads. Very often, such motors are used in robotics, medical equipment, in machines with frequency program control.
How motors work
In order to set in motion the rotor of a brushless DC motor, it is necessary to use a special microcontroller. It cannot be started in the same way as a synchronous or asynchronous machine. Using a microcontroller, it turns out to turn on the motor windings so that the direction of the magnetic field vectors on the stator and anchor are orthogonal.
In other words, with the help of the driver it turns out to regulate the torque that affects the rotor of the 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. But you can very quickly increase the speed of rotation of the rotor of the electric motor.
Differences between collector and brushless motors
The main difference is that on brushless electric motors for models there is no winding on the rotor. In the case of collector electric motors, there are windings on their rotors. But permanent magnets are mounted on the fixed part of the engine. In addition, a special collector 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 at 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 collector mounted on it rotate. At the same time, power is supplied to the next winding, a cycle is repeated.
The rotor speed 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, you do not need to use special microcontrollers, you can change the speed with a conventional variable resistor.
Features of brushless machines
But control of a brushless electric motor is impossible without the use of special controllers. Based on this, it can be concluded that motors of this type cannot be used as a generator. For efficient control, you can track the position of the rotor using several Hall sensors. With the help of such simple devices, it is possible to significantly improve the characteristics, but the cost of the electric motor will increase several times.
Starting brushless motors
It makes no sense to make microcontrollers yourself, buying a ready-made, albeit Chinese, one would be a much better option. But you must adhere to the following recommendations when choosing:
- Observe the maximum current rating. This parameter is sure to come in handy for various types of drive operation. The characteristic is often indicated by manufacturers directly in the name of the model. Very rarely, values characteristic of peak modes are indicated, in which the microcontroller cannot work for a long time.
- For continuous operation it is necessary to take into account the maximum value of the supply voltage.
- Be sure to consider the resistance of all internal circuits of the microcontroller.
- Be sure to take into account the maximum speed that is typical for the operation of this microcontroller. Please note that he will not be able to increase the maximum speed, since the restriction is done at the software level.
- Cheap models of microcontroller devices have a frequency of generated pulses in the range of 7 ... 8 kHz. Dear instances can be reprogrammed, and this parameter increases by 2-4 times.
Try to select microcontrollers for all parameters, as they affect the power that the electric motor can develop.
How is management
The electronic control unit allows the switching of 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.
In the event that there are no such devices, it is necessary to read the reverse voltage. It is generated in stator coils that are not currently connected. The controller is a hardware-software complex, it allows you to track all changes and specify the switching order as accurately as possible.
Three-phase brushless motors
A lot of brushless electric motors for aircraft models are powered by direct current. But there are three-phase instances in which the converters are installed. They allow you to make three-phase pulses from a constant voltage.
The work is as follows:
- Coil "A" receives pulses with a positive value. To coil "B" - with a negative value. As a result, the anchor will begin to move. The sensors record the offset and a signal is sent to the controller for the next switching.
- Coil “A” is disconnected, and a positive value pulse is supplied to winding “C”. Switching winding "B" does not undergo changes.
- A positive impulse hits coil "C", and a negative impulse arrives at "A".
- Then the pair “A” and “B” come into operation. They are served and the positive negative values of the pulses, respectively.
- Then a positive impulse is again fed to coil "B", and a negative pulse to "C".
- At the last stage, the “A” coil is turned on, to which a positive impulse arrives, and the negative 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 advantages that the drive receives when using brushless motors:
- Significantly greater resource than collector machines.
- High level of efficiency.
- Power is higher than that of collector motors.
- The rotation speed is much faster.
- During operation, sparks do not form, so they can be used in conditions with high fire hazard.
- Very simple operation of the drive.
- When working, you do not need to use additional components for cooling.
Among the shortcomings, a very high cost can be distinguished, given the price of the controller. Even briefly turn on to check the operability of such an electric motor does not work. In addition, repairing such motors is much more difficult due to their design features.