The emergence of brushless motors is explained by the need to create an electric machine with many advantages. A brushless motor is a device without a collector, the function of which is taken over by the electronics.

BKEPT - brushless DC motors, can be power, for example, 12, 30 volts.

• Selecting the right engine
• Principle of operation
• BKEPT device
• Sensors and their absence
• No sensor
• The concept of PWM frequency
• arduino system
• Engine Mount

Selecting the right engine

To select a unit, it is necessary to compare the principle of operation and features of collector and brushless motors.

From left to right: collector motor and motor FK 28-12 brushless

Collector ones cost less, but develop a low torque rotation speed. They operate on direct current, have a small weight and size, affordable repair by replacing parts. The manifestation of a negative quality is revealed when a huge number of turnovers are received. The brushes contact the commutator, causing friction that can damage the mechanism. The performance of the unit is reduced.

Brushes not only require repair due to rapid wear, but can also lead to overheating of the mechanism.

The main advantage of a brushless DC motor is the lack of torque and switching pins. This means that there are no sources of losses, as in permanent magnet motors. Their functions are performed by MOS transistors. Previously, their cost was high, so they were not available. Today, the price has become acceptable, and the performance has improved significantly. In the absence of a radiator in the system, the power is limited from 2.5 to 4 watts, and the operating current is from 10 to 30 amperes. The efficiency of brushless motors is very high.

The second advantage is the mechanics settings. The axle is mounted on wide bearings. There are no breaking and erasing elements in the structure.

The only negative is the expensive electronic control unit.

Consider an example of the mechanics of a CNC machine with a spindle.

Replacing the collector motor with a brushless one will protect the CNC spindle from breaking. Under the spindle is meant a shaft with right and left turns of torque. The CNC spindle is powerful. The speed of the torque is controlled by the servo tester, and the speed is controlled by the automatic controller. The cost of CNC with a spindle is about 4 thousand rubles.

Principle of operation

The main feature of the mechanism is the absence of a collector. And permanent magnets are installed at the spindle, which is the rotor. Around it are wire windings that have different magnetic fields. The difference between 12 volt brushless motors is the rotor control sensor located on it. The signals are fed into the speed controller unit.

BKEPT device

The layout of the magnets inside the stator is usually used for two-phase motors with a small number of poles. The principle of torque around the stator is used when it is necessary to obtain a two-phase motor with low speed.

There are four poles on the rotor. Rectangle-shaped magnets are installed by alternating poles. However, the number of poles is not always equal to the number of magnets, which can be 12, 14. But the number of poles must be even. Several magnets can make up one pole.

The picture shows 8 magnets forming 4 poles. The moment of force depends on the power of the magnets.

Sensors and their absence

Travel controllers are divided into two groups: with and without a rotor position sensor.

Current forces are applied to the motor windings at a special position of the rotor. It is determined by the electronic system using a position sensor. They are of various types. A popular travel controller is a discrete Hall effect sensor. A three-phase 30 volt motor will use 3 sensors. The electronics unit constantly has data on the position of the rotor and directs the voltage in time to the desired windings.

A common device that changes its conclusions when switching windings.

An open loop device measures current, speed. PWM channels are attached to the bottom of the control system.

Three inputs are connected to the Hall sensor. In the event of a change in the Hall sensor, the process of processing the interrupt begins. To ensure fast response handling of the interrupt, a Hall sensor is connected to the lower pins of the port.

Using a position sensor with a microcontroller

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The cascade strength controller is at the heart of the AVR core, which provides intelligent control of a brushless DC motor. AVR is a chip for performing certain tasks.

The principle of operation of the stroke controller can be with or without a sensor. The AVR board program does:

• starting the engine as quickly as possible without the use of external additional devices;
• speed control by one external potentiometer.

A separate type of automatic control sma, used in washing machines.

No sensor

To determine the position of the rotor, it is necessary to measure the voltage on the idle winding. This method is applicable when the motor is rotating, otherwise it will not work.

Sensorless travel controllers are lighter in weight, which explains their widespread use.

Controllers have the following properties:

• value of maximum direct current;
• the value of the maximum operating voltage;
• number of maximum revolutions;
• resistance of power switches;
• impulse frequency.

When connecting the controller, it is important to keep the wires as short as possible. Due to the occurrence of current surges at the start. If the wire is long, then errors in determining the position of the rotor may occur. Therefore, the controllers are sold with a wire of 12 - 16 cm.

Controllers have many software settings:

• engine shutdown control;
• soft or hard shutdown;
• braking and smooth shutdown;
• advancing power and efficiency;
• soft, hard, quick start;
• current limit;
• gas mode;
• direction change.

The LB11880 controller shown in the figure contains a powerful brushless motor driver, that is, you can run the motor directly to the microcircuit without additional drivers.

The concept of PWM frequency

When the keys are turned on, the full load is applied to the engine. The unit reaches maximum speed. In order to control the motor, you need to provide a power regulator. This is exactly what pulse-width modulation (PWM) does.

The required frequency of opening and closing keys is set. The voltage changes from zero to working. To control the speed, it is necessary to superimpose the PWM signal on the key signals.

The PWM signal can be generated by the device on several outputs. Or create a PWM for a separate key with a program. The circuit becomes simpler. The PWM signal has 4-80 kilohertz.

Increasing the frequency leads to more transition processes, which gives rise to heat. The height of the PWM frequency increases the number of transients, which results in losses on the keys. A small frequency does not give the desired smoothness of control.

To reduce the losses on the keys during transients, PWM signals are applied to the upper or lower switches separately. Direct losses are calculated by the formula P=R*I2, where P is the loss power, R is the switch resistance, I is the current strength.

Less resistance minimizes losses, increases efficiency.

arduino system

Often, the arduino hardware computing platform is used to control brushless motors. It is based on a board and a development environment in the Wiring language.

The arduino board includes an Atmel AVR microcontroller and element programming and interaction with circuits. The board has a voltage regulator. The Serial Arduino board is a simple inverting circuit for converting signals from one level to another. Programs are installed via USB. Some models, such as the Arduino Mini, require an additional programming board.

The Arduino programming language uses Standard Processing. Some arduino models allow you to control multiple servers at the same time. Programs are processed by the processor, and compiled by the AVR.

Problems with the controller can occur due to voltage dips and excessive load.

Engine Mount

A motor mount is a mechanism that mounts an engine. Used in engine installations. The motor mount consists of interconnected rods and frame elements. Motor mounts are flat, spatial in terms of elements. Motor mount for a single 30 volt motor or multiple devices. The power circuit of the motor mount consists of a set of rods. The motor mount is installed in a combination of truss and frame elements.

The brushless DC motor is an indispensable unit used both in everyday life and in industry. For example, CNC machine, medical equipment, automotive mechanisms.

BKEPT are distinguished by reliability, high-precision principle of operation, automatic intelligent control and regulation.

As soon as I started doing aircraft modeling, I immediately became interested in why the engine has three wires, why it is so small and at the same time so powerful and why it needs a speed controller ... Time passed, and I figured everything out. And then he set himself the task of making a brushless motor with his own hands.

The principle of operation of the electric motor:
The basis of the operation of any electrical machine is the phenomenon of electromagnetic induction. Therefore, if a loop with a current is placed in a magnetic field, then it will be affected by ampere power, which will create a torque. The frame will begin to turn and stop in the position of the absence of the moment created by the Ampere force.

Electric motor device:
Any electric motor consists of a fixed part - stator and moving part Rotor. In order to start rotation, you need to change the direction of the current in turn. This function is performed Collector(brushes).

A brushless motor is a motor DIRECT CURRENT without a collector, in which the functions of the collector are performed by electronics. (If the motor has three wires, this does not mean that it is powered by three-phase AC! It is powered by "portions" of short pulses of DC, and I do not want to shock you, but the same motors that are used in coolers are also brushless, although they and have only two DC power wires)

Brushless motor device:
Inrunner(pronounced "inrunner"). The engine has windings located on the inner surface of the housing, and a magnetic rotor rotating inside.


Outrunner(pronounced "outrunner"). The engine has fixed windings (inside) around which the body rotates with permanent magnets placed on its inner wall.

Principle of operation:
In order for a brushless motor to start rotating, voltage must be applied to the motor windings synchronously. Synchronization can be organized using external sensors (optical or hall sensors), and on the basis of back EMF (sensorless), which occurs in the motor during its rotation.

Sensorless control:
There are brushless motors without any position sensors. In such motors, the determination of the position of the rotor is performed by measuring the EMF in the free phase. We remember that at each moment of time, “+” is connected to one of the phases (A) and “-” power is connected to the other (B), one of the phases remains free. Rotating, the motor induces an EMF (i.e., as a result of the law of electromagnetic induction, an induction current is formed in the coil) in a free winding. As it rotates, the voltage on the free phase (C) changes. By measuring the voltage on the free phase, you can determine the moment of switching to the next position of the rotor.
To measure this voltage, the "virtual point" method is used. The bottom line is that, knowing the resistance of all windings and the initial voltage, you can virtually "shift the wire" to the junction of all windings:
Brushless Motor Speed ​​Controller:
A brushless motor without electronics is just a piece of iron, because. in the absence of a regulator, we cannot simply apply voltage to it so that it just starts normal rotation. The speed controller is a rather complex system of radio components, because. she must:
1) Determine the initial position of the rotor to start the motor
2) Drive the motor at low speeds
3) Accelerate the motor to the nominal (set) rotation speed
4) Maintain maximum torque

Schematic diagram of the speed controller (valve):


Brushless motors were invented at the dawn of the advent of electricity, but no one could make a control system for them. And only with the development of electronics: with the advent of powerful semiconductor transistors and microcontrollers, brushless motors began to be used in everyday life (the first industrial use was in the 60s).

Advantages and disadvantages of brushless motors:

Advantages:
-Frequency of rotation varies in a wide range
-Ability to use in explosive and aggressive environments
-High torque capacity
-High energy performance (efficiency over 90%)
-Long service life, high reliability and increased service life due to the absence of sliding electrical contacts

Flaws:
-Relatively complex engine management system
-High cost of the engine due to the use of expensive materials in the design of the rotor (magnets, bearings, shafts)
Having dealt with the theory, let's move on to practice: we will design and make an engine for the MX-2 flight model.

List of materials and equipment:
1) Wire (taken from old transformers)
2) Magnets (bought online)
3) Stator (lamb)
4) Shaft
5) Bearings
6) Duralumin
7) Heat shrink
8) Access to unlimited tech junk
9) Access to tools
10) Straight arms :)

Progress:
1) From the very beginning we decide:

Why do we make an engine?
What should it be designed for?
Where are we limited?

In my case: I am making an engine for an airplane, so let it be of external rotation; it should be designed for the fact that it should give out 1400 grams of thrust with a three-can battery; I am limited in weight and size. However, where do you start? The answer to this question is simple: from the most difficult part, i.e. with a part that is easier to just find, and everything else to fit it. I did so. After many unsuccessful attempts to make a mild steel sheet stator, it became clear to me that it was better to find one. I found it in an old video head from a video recorder.

2) The winding of a three-phase brushless motor is carried out with an insulated copper wire, the cross section of which determines the value of the current strength, and hence the motor power. It is unforgettable that the thicker the wire, the more revolutions, but the weaker the torque. Section selection:

1A - 0.05mm; 15A - 0.33mm; 40A - 0.7mm

3A - 0.11mm; 20A - 0.4mm; 50A - 0.8mm

10A - 0.25mm; 30A - 0.55mm; 60A - 0.95mm


3) We begin to wind the wire on the poles. The more turns (13) wound around the tooth, the greater the magnetic field. The stronger the field, the greater the torque and the smaller the number of revolutions. To get high speeds, you need to wind a smaller number of turns. But along with this, the torque also drops. To compensate for the torque, a higher voltage is usually applied to the motor.
4) Next, choose the method of connecting the winding: a star or a triangle. A star connection gives more torque but fewer turns than a delta connection by a factor of 1.73. (subsequently a delta connection was chosen)

5) Choose magnets. The number of poles on the rotor must be even (14). The shape of the magnets used is usually rectangular. The size of the magnets depends on the geometry of the motor and the characteristics of the motor. The stronger the magnets used, the higher the moment of force developed by the motor on the shaft. Also, the greater the number of poles, the greater the moment, but less revolutions. The magnets on the rotor are fixed with a special hot melt adhesive.

I tested this engine on a spin-motor installation that I created, which allows you to measure thrust, power and engine speed.

To see the differences between the star and delta connections, I connected the windings in different ways:

The result was an engine corresponding to the characteristics of the aircraft, the mass of which is 1400 grams.

Characteristics of the resulting engine:
Current consumption: 34.1A
No-load current: 2.1A
Winding resistance: 0.02 ohm
Number of poles: 14
Turnovers: 8400 rpm

Video report of an engine test on an airplane ... Soft landing: D

Engine efficiency calculation:


A very good indicator ... Although it could have been even higher ...

Conclusions:
1) Brushless motors have high efficiency and efficiency
2) Brushless motors are compact
3) Brushless motors can be used in explosive environments
4) Star connection gives more torque but 1.73 times fewer turns than delta connection.

Thus, to make your own brushless motor for an aerobatic model aircraft is task is feasible

If you have questions or something is not clear to you, ask me questions in the comments of this article. Good luck everyone)

A DC motor is an electric motor that is powered by direct current. If necessary, obtain a high-torque motor with relatively low speed. Structurally, Inrunners are simpler due to the fact that the fixed stator can serve as a housing. Mounting devices can be mounted to it. In the case of Outrunners, the entire outer part rotates. The engine is fastened by a fixed axle or stator parts. In the case of a motor-wheel, the fastening is carried out for the fixed axis of the stator, the wires are brought to the stator through a hollow axis of which is less than 0.5 mm.

An AC motor is called electric motor powered by alternating current. There are the following types of AC motors:

There is also a UKD (universal commutator motor) with the function of operating mode both on alternating and direct current.

Another type of engine is stepper motor with a finite number of rotor positions. A certain indicated position of the rotor is fixed by supplying power to the necessary corresponding windings. When the supply voltage is removed from one winding and transferred to others, a process of transition to another position occurs.

An AC motor when powered by a commercial network usually does not achieve speeds of more than three thousand revolutions per minute. For this reason, when it is necessary to obtain higher frequencies, a collector motor is used, the additional advantages of which are lightness and compactness while maintaining the required power.

Sometimes a special transmission mechanism called a multiplier is also used, which changes the kinematic parameters of the device to the required technical indicators. Collector assemblies sometimes occupy up to half the space of the entire motor, so AC motors are reduced in size and made lighter in weight through the use of a frequency converter, and sometimes due to the presence of a network with an increased frequency of up to 400 Hz.

The resource of any asynchronous AC motor is noticeably higher than the collector one. It is determined state of insulation of windings and bearings. A synchronous motor, when using an inverter and a rotor position sensor, is considered an electronic analogue of a classic collector motor that supports DC operation.

Brushless DC motor. General information and device device

A brushless DC motor is also called a three-phase brushless motor. It is a synchronous device, the principle of operation of which is based on self-synchronized frequency regulation, due to which the vector (starting from the position of the rotor) of the stator magnetic field is controlled.

These types of motor controllers are often powered by DC voltage, hence the name. In the English-language technical literature, the brushless motor is called PMSM or BLDC.

The brushless motor was created primarily to optimize the any DC motor generally. Very high demands were placed on the actuator of such a device (especially on a high-speed microdrive with precise positioning).

This, perhaps, led to the use of such specific DC devices, brushless three-phase motors, also called BLDTs. By their design, they are almost identical to AC synchronous motors, where the rotation of the magnetic rotor occurs in a conventional laminated stator in the presence of three-phase windings, and the number of revolutions depends on the voltage and loads of the stator. Based on certain coordinates of the rotor, different stator windings are switched.

Brushless DC motors can exist without any separate sensors, however, sometimes they are present on the rotor, such as a Hall sensor. If the device works without an additional sensor, then stator windings act as a fixing element. Then the current arises due to the rotation of the magnet, when the rotor induces an EMF in the stator winding.

If one of the windings is turned off, then the signal that was induced will be measured and further processed, however, such a principle of operation is impossible without a signal processing professor. But to reverse or brake such an electric motor, a bridge circuit is not needed - it will be enough to supply control pulses to the stator windings in the reverse sequence.

In the VD (switched motor), the inductor in the form of a permanent magnet is located on the rotor, and the armature winding is on the stator. Based on the position of the rotor, the supply voltage of all windings is formed electric motor. When used in such constructions of the collector, its function will be performed in the valve motor by a semiconductor switch.

The main difference between synchronous and brushless motors is the self-synchronization of the latter with the help of DPR, which determines the proportional frequency of rotation of the rotor and the field.

Most often, a brushless DC motor finds application in the following areas:

stator

This device has a classic design and resembles the same device of an asynchronous machine. The composition includes copper winding core(laid around the perimeter into the grooves), which determines the number of phases, and the housing. Usually, the sine and cosine phases are sufficient for rotation and self-starting, however, often the valve motor is made three-phase and even four-phase.

Electric motors with reverse electromotive force according to the type of coiling on the stator winding are divided into two types:

• sinusoidal form;
• trapezoidal shape.

In the corresponding types of motor, the electric phase current also changes according to the method of supply sinusoidally or trapezoidal.

Rotor

Usually the rotor is made of permanent magnets with two to eight pairs of poles, which, in turn, alternate from north to south or vice versa.

The most common and cheapest for the manufacture of the rotor are ferrite magnets, but their disadvantage is low level of magnetic induction, therefore, devices made from alloys of various rare earth elements are now replacing this material, since they can provide a high level of magnetic induction, which, in turn, allows to reduce the size of the rotor.

DPR

The rotor position sensor provides feedback. According to the principle of operation, the device is divided into the following subspecies:

• inductive;
• photoelectric;
• Hall effect sensor.

The latter type is the most popular due to its almost absolute inertialess properties and the ability to get rid of the delay in the feedback channels by the position of the rotor.

Control system

The control system consists of power switches, sometimes also of thyristors or power transistors, including an insulated gate, leading to the collection of a current inverter or a voltage inverter. The process of managing these keys is most often implemented by using a microcontroller, which requires a huge amount of computational operations to control the engine.

Principle of operation

The operation of the engine is that the controller switches a certain number of stator windings in such a way that the vector of the magnetic fields of the rotor and stator are orthogonal. With PWM (Pulse Width Modulation) the controller controls the current flowing through the motor and regulates the torque exerted on the rotor. The direction of this acting moment is determined by the mark of the angle between the vectors. Electrical degrees are used in calculations.

Switching should be carried out in such a way that Ф0 (rotor excitation flux) is kept constant relative to the armature flux. When such excitation and the armature flow interact, a torque M is formed, which tends to turn the rotor and in parallel ensure that the excitation and the armature flow coincide. However, during the rotation of the rotor, the various windings are switched under the influence of the rotor position sensor, as a result of which the armature flux turns towards the next step.

In such a situation, the resulting vector shifts and becomes stationary with respect to the rotor flux, which, in turn, creates the necessary torque on the motor shaft.

Engine management

The controller of a brushless DC electric motor regulates the moment acting on the rotor by changing the value of the pulse-width modulation. Switching is controlled and carried out electronically, unlike a conventional brushed DC motor. Also common are control systems that implement pulse-width modulation and pulse-width regulation algorithms for the workflow.

Vector controlled motors provide the widest known range for self speed control. The regulation of this speed, as well as maintaining the flux linkage at the required level, is due to the frequency converter.

A feature of the regulation of the electric drive based on vector control is the presence of controlled coordinates. They are in a fixed system and converted to rotating, highlighting a constant value proportional to the controlled parameters of the vector, due to which a control action is formed, and then a reverse transition.

Despite all the advantages of such a system, it is also accompanied by a disadvantage in the form of the complexity of controlling the device for controlling the speed in a wide range.

Advantages and disadvantages

Nowadays, in many industries, this type of motor is in great demand, because the brushless DC motor combines almost all the best qualities of non-contact and other types of motors.

The undeniable advantages of the brushless motor are:

Despite significant positives, brushless DC motor also has a few disadvantages:

Based on the foregoing and the underdevelopment of modern electronics in the region, many still consider it appropriate to use a conventional asynchronous motor with a frequency converter.

Three-phase brushless DC motor

This type of motor has excellent performance, especially when performing control by means of position sensors. If the moment of resistance varies or is not known at all, and also if it is necessary to achieve higher starting torque sensor control is used. If the sensor is not used (usually in fans), the control eliminates the need for wired communication.

Features of controlling a three-phase brushless motor without a position sensor:

Control Features three-phase brushless motor with position encoder using the example of a Hall effect sensor:

Conclusion

A brushless DC motor has a lot of advantages and will be a worthy choice for use by both a specialist and a simple layman.

Recently, brushless DC motors have become increasingly popular. They are actively used in instrumentation, industrial medical and household automation, as well as in instrumentation. This type of motor works without brushes, all switching is carried out using electronic devices.

Benefits of brushless motors

Brushless motors have a number of advantages that have determined their areas of application. They have the best performance. Their torque is much higher than conventional motors. Brushless designs are characterized by higher dynamic performance and efficiency.

Other benefits include quieter operation, longer service life and higher rotational speeds. The motor size to torque ratio is higher than other types. This is especially important in areas where size and weight are critical factors.

Working principle of brushless motor

The principle of operation is based on the magnetic fields produced by the stator and rotor, the rotational speed of which is the same. There is no so-called slip characteristic of asynchronous motors. The configuration of brushless motors is single-phase, two-phase or three-phase. The number of windings in the stator depends on this. The most widespread in all areas are three-phase motors.

Brushless motor device

As an example, consider the most popular three-phase brushless motor. It has a stator made of laminated steel, in the grooves of which the winding is placed. Most motors of this type have three windings connected in a star.

The rotor is a permanent magnet with 2 to 8 pairs of poles. At the same time, the South and North poles alternate with each other. The rotor is made of a special magnetic material that provides the required magnetic field density. As a rule, these are ferrite magnets, from which permanent magnets are made.

Unlike conventional electric motors, brushless DC motors are electronically commutated. This is due to the need to consistently supply voltage to the stator windings. At the same time, it is necessary to know what position the rotor is in. This position is determined by Hall sensors, which give a high or low signal, depending on which pole passes near the highly sensitive elements.

Brushless DC Generator

Household and medical appliances, aeromodelling, pipe shut-off drives for gas and oil pipelines - this is not a complete list of applications for brushless DC motors (BD). Let's look at the device and principle of operation of these electromechanical drives in order to better understand their advantages and disadvantages.

General information, device, scope

One of the reasons for the interest in the DB is the increased need for high-speed micromotors with precise positioning. The internal structure of such drives is shown in Figure 2.

Rice. 2. The device of the brushless motor

As you can see, the design is a rotor (armature) and a stator, the first has a permanent magnet (or several magnets arranged in a certain order), and the second is equipped with coils (B) to create a magnetic field.

It is noteworthy that these electromagnetic mechanisms can be either with an internal anchor (this type of construction can be seen in Figure 2) or external (see Figure 3).

Rice. 3. Design with an external anchor (outrunner)

Accordingly, each of the designs has a specific scope. Devices with an internal armature have a high rotation speed, therefore they are used in cooling systems, as power plants for drones, etc. External rotor drives are used where precise positioning and resistance to torque overloads are required (robotics, medical equipment, CNC machines, etc.).

Principle of operation

Unlike other drives, for example, an AC induction machine, a special controller is required for the operation of the DB, which turns on the windings in such a way that the vectors of the magnetic fields of the armature and the stator are orthogonal to each other. That is, in fact, the driver device regulates the torque acting on the DB armature. This process is clearly shown in Figure 4.

As you can see, for each movement of the armature, it is necessary to perform a certain commutation in the stator winding of a brushless motor. This principle of operation does not allow smooth control of rotation, but makes it possible to quickly gain momentum.

Differences between brushed and brushless motors

The collector-type drive differs from the BD both in design features (see Fig. 5.) and in the principle of operation.

Rice. 5. A - collector motor, B - brushless

Let's take a look at the design differences. Figure 5 shows that the rotor (1 in Fig. 5) of a collector-type motor, unlike a brushless one, has coils that have a simple winding scheme, and permanent magnets (usually two) are installed on the stator (2 in Fig. 5 ). In addition, a collector is installed on the shaft, to which brushes are connected that supply voltage to the armature windings.

Briefly describe the principle of operation of collector machines. When voltage is applied to one of the coils, it is excited and a magnetic field is formed. It interacts with permanent magnets, this causes the armature and the collector placed on it to rotate. As a result, power is supplied to the other winding and the cycle repeats.

The frequency of rotation of an armature of this design directly depends on the intensity of the magnetic field, which, in turn, is directly proportional to the voltage. That is, to increase or decrease the speed, it is enough to increase or decrease the power level. And to reverse it is necessary to switch the polarity. This control method does not require a special controller, since the travel controller can be made based on a variable resistor, and a conventional switch will work as an inverter.

We considered the design features of brushless motors in the previous section. As you remember, their connection requires a special controller, without which they simply will not work. For the same reason, these motors cannot be used as a generator.

It is also worth noting that in some drives of this type, for more efficient control, the positions of the rotor are monitored using Hall sensors. This significantly improves the characteristics of brushless motors, but leads to an increase in the cost of an already expensive design.

How to start a brushless motor?

To make this type of drive work, a special controller is required (see Figure 6). Without it, launch is impossible.

Rice. 6. Brushless Motor Controllers for Modeling

It makes no sense to assemble such a device yourself, it will be cheaper and more reliable to purchase a ready-made one. You can select it according to the following characteristics inherent in PWM channel drivers:

• The maximum allowable current, this characteristic is given for the normal operation of the device. Quite often, manufacturers indicate this parameter in the model name (for example, Phoenix-18). In some cases, a value is given for peak mode, which the controller can maintain for several seconds.
• The maximum nominal voltage for continuous operation.
• The resistance of the internal circuits of the controller.
• Permissible number of revolutions, indicated in rpm. Above this value, the controller will not allow to increase the rotation (the restriction is implemented at the software level). Please note that the speed is always given for 2-pole drives. If there are more pole pairs, divide the value by their number. For example, the number 60000 rpm is indicated, therefore, for a 6-magnet motor, the rotational speed will be 60000/3=20000 prm.
• The frequency of the generated pulses, for most controllers, this parameter ranges from 7 to 8 kHz, more expensive models allow you to reprogram the parameter, increasing it to 16 or 32 kHz.

Note that the first three characteristics determine the capacity of the database.

Brushless motor control

As mentioned above, the commutation of the drive windings is controlled electronically. To determine when to switch, the driver monitors the position of the armature using Hall sensors. If the drive is not equipped with such detectors, then the back EMF that occurs in the unconnected stator coils is taken into account. The controller, which, in fact, is a hardware-software complex, monitors these changes and sets the switching order.

Three-phase brushless DC motor

Most databases are performed in a three-phase design. To control such a drive, the controller has a DC to three-phase pulse converter (see Fig. 7).

Figure 7. DB voltage diagrams

To explain how such a brushless motor works, one should consider Figure 4 together with Figure 7, where all stages of the drive operation are shown in turn. Let's write them down:

1. A positive impulse is applied to coils "A", while a negative impulse is applied to "B", as a result, the armature will move. The sensors will record its movement and give a signal for the next commutation.
2. Coil "A" is turned off, and a positive pulse goes to "C" ("B" remains unchanged), then a signal is given to the next set of pulses.
3. On "C" - positive, "A" - negative.
4. A pair of "B" and "A" works, which receive positive and negative impulses.
5. A positive pulse is re-applied to "B", and a negative pulse to "C".
6. Coils "A" are turned on (+ is supplied) and a negative pulse is repeated on "C". Then the cycle repeats.

In the apparent simplicity of management there are a lot of difficulties. It is necessary not only to track the position of the armature in order to produce the next series of pulses, but also to control the rotational speed by adjusting the current in the coils. In addition, you should choose the most optimal parameters for acceleration and deceleration. It is also worth noting that the controller must be equipped with a block that allows you to control its operation. The appearance of such a multifunctional device can be seen in Figure 8.

Rice. 8. Multi-function brushless motor controller

Advantages and disadvantages

An electric brushless motor has many advantages, namely:

• The service life is much longer than that of conventional collector counterparts.
• High efficiency.
• Quick set to maximum rotation speed.
• It is more powerful than CD.
• The absence of sparks during operation allows the drive to be used in fire hazardous conditions.
• No additional cooling required.
• Simple operation.

Now let's look at the cons. A significant drawback that limits the use of databases is their relatively high cost (taking into account the price of the driver). Among the inconveniences is the impossibility of using the database without a driver, even for short-term activation, for example, to check the performance. Problem repair, especially if rewinding is required.