Basic knowledge of UAV - composition - model aircraft motor

Model aircraft motor

There are brush and brushless motors. Structurally, the brushless motor is similar to the brushed motor, and also has a rotor and a stator, but the structure of the brushed motor is opposite; the rotor of the brushed motor is a coil winding, which is connected to the power output shaft, and the stator is a permanent magnet magnet. Steel; the rotor of the brushless motor is a permanent magnet steel, which is connected to the output shaft together with the outer casing, and the stator is a winding coil. Brushless motor).
brushed motor

Brushed motors are motors that contain commutated brushes inside. What is a brush, directly on the picture. The brush is fixed on the back cover of the motor through the insulating seat, and the positive and negative poles of the power supply are introduced to the commutator of the rotor, and the commutator is connected to the coil on the rotor. The magnet creates a force and turns. The picture below shows the brushes and commutator after dismantling the motor currently used by Crazepony.

Due to the physical contact between the brushes and the commutator, the brushed motor has disadvantages such as large friction, large heat generation, and low efficiency. However, the brushed motor also has the advantages of simple manufacture and low cost, so the brushed motor still occupies a large share on the market.

Brushless Motor

The brushed motor rotates by obtaining the magnetic field force in a fixed direction through the structural design of the brush and the commutator. The brushless motor has no brushes and commutators. How does it obtain the magnetic field force in a fixed direction? 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, and this magnetic field drives the permanent magnet magnet on the rotor to rotate, The motor turned on.

The performance of the motor is related to factors such as the number of magnets, the magnetic flux strength of the magnet, and the input voltage of the motor, and is also closely related to the control performance of the brushless motor.

The brushless motor has the advantages of sufficient power, long life and high efficiency. Therefore, the big four axes all use brushless motors. The appearance of the model brushless motors is as follows, which is different from the brushless motors. The most obvious thing is that the brushless motors have three wires and are used with the ESC.

The most important parameter of the brushless motor is the KV value, which is a unique performance parameter of the brushless motor and an important data for judging the performance characteristics of the brushless motor.

  • The brushless motor KV value is defined as speed/volt, which means that the input voltage increases by 1 volt, and the speed value (rev/min) of the brushless motor idling speed increases.
  • From this definition, we can know that the input of the brushless motor voltage and the idling speed of the motor follow a strict linear proportional relationship.

For example, the KV value of a brushless motor is 1000KV, which means that the motor rotates at 1000 rpm under 1V voltage. Then under 10V voltage, the motor speed is: 10V*1000KV=10000 rpm, of course, these are all when the motor is no-load.

  • The number of winding turns is large, the KV value is low, the maximum output current is small, but the torque is large.
  • The smaller the number of winding turns, the higher the KV value, the higher the maximum output current, but the smaller the torque.

It can be expanded here. Why do quadcopters use external rotor brushless DC motors? In the outer rotor motor, the magnetic steel originally in the central position is made into pieces and attached to the casing. When the motor is running, the entire casing is rotating, while the coil stator in the middle does not move. Compared with the inner rotor, the outer rotor brushless DC motor has a much larger moment of inertia of the rotor (because the main mass of the rotor is concentrated on the casing), so the speed is slower than that of the inner rotor motor, and the KV value is usually several hundred to several thousand. In between, the propeller can be directly driven on the model aircraft, and the mechanical deceleration mechanism is omitted. (Excerpted from "Complete Guide to ESC Design of Inductive Brushless DC Motors")

Motor hollow cup

The coreless motor is a DC, permanent magnet and servo micro-motor. The hollow cup motor breaks through the rotor structure form of the traditional motor in structure, and adopts an ironless rotor. The hollow cup motor has outstanding energy saving, control and drag characteristics.

The hollow cup motor is divided into two types: brushed and brushless. The brushless hollow cup motor rotor has no iron core, and the brushless hollow cup motor stator has no iron core.

motor model

I often see people talking about 2212 motors, 2204 motors, etc. What does it mean? This is actually the size of the motor.

No matter what brand of motor is, it must correspond to 4 digits of this type, of which the first 2 digits are the diameter of the motor rotor, and the last 2 digits are the height of the motor rotor. Note, not the shell. To put it simply, the larger the first two digits, the fatter the motor, and the larger the last two digits, the higher the motor. For example, the common 2212 motor is generally used for aerial photography with a wheelbase of 450, and the 2204 motor is generally used for a traversing aircraft with a wheelbase of 210.

For hollow cup motors, the naming is also using two numbers, diameter and height, but generally refers to the size of the housing. Such as 720 motor, 615 motor and so on.