1. Rated voltage
The suitable working voltage of the brushless motor, in fact, the suitable working voltage of the brushless motor is very wide, and the rated voltage is the result of the specified load condition. For example, 2212-850KV motor specifies the load of 1045 propeller, and its rated working voltage is 11V. If the load is reduced, for example with a 7040 propeller, the motor can work under 22V voltage. However, this operating voltage does not rise indefinitely, and is mainly restricted by the highest frequency supported by the electronic controller. Therefore, the rated work is determined by the working environment.
2. KV value
The brushed DC motor is marked with the rated speed according to the rated working voltage. The brushless motor introduces the concept of KV value, so that the user can intuitively know the specific speed of the brushless motor under the specific working voltage. Actual speed = KV value * working voltage, this is the actual meaning of KV, which is the speed per minute under 1V working voltage. The speed of the brushless DC motor is proportional to the voltage, and the speed of the motor will rise linearly with the increase in voltage. For example, the speed of a 2212-850KV motor at a voltage of 10V is: 850*10=8500RPM (RPM, speed per minute).
The KV value and the number of turns are in inverse proportion. For example, 2212-850KV, the number of turns is 30T (15 turns), the KV value in the case of 28T is: 850KV*30T/28T=910KV.
3. Torque and speed
Torque: (torque, torque) the driving torque generated by the rotor in the motor that can be used to drive the mechanical load. We can understand the power of the motor.
Speed: The speed of the motor per minute.
The torque and speed of a motor are always in a trade-off relationship in the same motor. It can be basically considered that the product of torque and speed is a fixed number, that is, the higher the speed of the same motor, the lower the torque. The opposite is still true. It is impossible to require a motor to have a higher speed and a higher torque. This rule applies to all motors. For example: 2212-850KV motor can drive 1045 propellers under the condition of 11V. If the voltage is doubled, its speed will also be doubled. If the load is still 1045 propellers at this time, the motor will quickly change due to current and temperature. The sharp rise and burn down.
4. Maximum current and maximum power
Maximum current: the maximum current that the motor can withstand and work safely
Maximum power: the maximum power that the motor can withstand and work safely Power = voltage * current
Each motor has its own upper limit of power, the maximum power is this upper limit, if the working conditions exceed this maximum power, it will cause the motor to burn at high temperature. Of course, the maximum power is also obtained when the working voltage is specified. If it is at a higher working voltage, the reasonable maximum power will also increase. This is because: Q=I², the heat of the conductor is proportional to the square of the current. At a higher voltage, if it is the same power, the current will drop and the heat will decrease, which will increase the maximum power.
This also explains why a large number of 22.2V or even 30V batteries are used to drive multi-axis aircraft in professional aerial photography aircraft. The brushless motor under high voltage has low current, low heat and higher efficiency.
5. Slot pole structure (N: number of slots, P: number of poles)
The common internal rotor brushless motor structures of the model are: 3N2P (commonly used in induction motors), 12N4P (most internal rotor motors)
The common external rotor brushless motor structures of the model are: 9N6P, 9N12P, 12N8P, 12N10P, 12N14P, 18N16P, 24N20P.
The reason why the number of poles of the inner rotor brushless motor used in the model is not high: At present, the inner rotor motor is mostly used for deceleration, so the required speed is relatively high. Electronic speed = actual speed * motor pole pair number. The maximum electronic speed supported by the electronic controller is often a fixed number, so if the motor pole pair number is too high, the maximum motor speed supported will decrease, so the current inner rotor motor The number of poles is all 4 or less.
About 12N4P inner rotor motor: It is an integer slot motor, which is widely used in the model inner rotor motor, and the motor uses a single-layer winding distributed winding.
The external rotor motors used in the model are all fractional slot motors, and their structural features and performance are as follows:
1. N must be a multiple of 3, and P must be an even number (the magnetic steel must be in pairs, so it must be an even number).
2. The smaller the P number, the higher the maximum speed. For example, the maximum speed of 12N10P is definitely higher than that of 12N16P, and vice versa.
3. If N is larger than P, the relative speed is higher. The maximum speed of 9N6P is definitely higher than 9N12P, and vice versa.
5. For the same N and P, the larger the torque, the stronger the torque. Torque, 12N16P is greater than 12N14P is greater than 12N10P.
6. N and P cannot be divisible, such as 12N6P.
Outer rotor slot structure and application areas: 9N6P deceleration is used in 400-500 level helicopter models and small ducts, 9N12P direct drive is used in small fixed wing or other models, 12N8P deceleration is used in 500-700 helicopter models or direct drive use For medium and large ducts, 12N10P deceleration is used in 600-800 helicopter models, 12N14P direct drive is used in most fixed wing and ship models, and brushless motors with a structure higher than 12 slots are more common in multi-axis aircraft.
5. Inductive and non-inductive motors
The advantages of induction motors: high operating accuracy and smooth start-up
Disadvantages of induction motors:
1. The reliability of the system is reduced due to the presence of sensors under conditions such as high temperature and vibration.
2. Too many sensor connecting wires are inconvenient to install and easily cause electromagnetic interference.
3. The installation accuracy of the sensor directly affects the running performance of the motor, especially when it is difficult to guarantee the installation accuracy of a multi-pole motor.
4. Occupies space and limits the miniaturization of motors.
The advantages of non-inductive motors: simple structure, low cost, convenient installation
Disadvantages of non-inductive motors: the rotor position detection accuracy is reduced, the running accuracy is reduced, and the start-up is not as stable as the inductive motor.
What is an inductive motor: Traditional brushless motors are equipped with Hall sensors, which use Hall sensors to detect the position of the rotor to achieve steering.
What is a non-inductive motor: remove the Hall sensor, and use the electronic controller to detect the change of the back electromotive force of the motor to determine the rotor position to achieve steering. To
Six, the outer rotor is brushless and the inner rotor is brushless
The advantages of the outer rotor brushless motor: large moment of inertia, stable rotation, large torque, and good fixation of magnets.
Disadvantages of the outer rotor brushless motor: the stator heat cannot be discharged, the internal working environment is closed, and external debris may enter the motor and affect the operation.
The advantages of the inner rotor brushless motor: the windings are in direct contact with the shell, and the heat can be directly discharged. The inside of the motor is isolated from the outside, preventing external debris from entering the inside.
Disadvantages of the inner rotor brushless motor: the torque is not as good as the outer rotor brushless motor, and the magnet fixing is more complicated.
Seven, common motor types
The concept of a motor: a motor refers to an electromagnetic device that uses the law of electromagnetic induction to convert electrical energy.
Motors include: motors, generators, transformers
According to the working power supply, it can be divided into: DC motor, AC motor, AC and DC motor
DC motors mainly include: permanent magnet DC motors, permanent magnet brushless motors
The excitation methods of DC motor installation mainly include: separate excitation, series excitation, compound excitation, and parallel excitation.
AC motors mainly include: single-phase asynchronous motors, three-phase asynchronous motors.
Recommended Readingd : Basic Introduction Of Brushless DC Hub Motor(1)