About aircraft model motor

Current model power's basic configuration is "brushless motor" plus ESC combination of programs, most of whom we call such a motor as a "brushless motor", some people call it the BLDCM.

First of all, it is called DC brushless motor is a certain problem, the data show that the square wave-driven BLDCM back-EMF is similar to the trapezoidal wave, trapezoidal back-EMF is not accidental formation, but artificial control, mainly used Whole concentrated winding, the shape of the permanent magnet tile, multi-radial magnetization and so on. This type of motor is suitable for square wave control, which is commonly used model aircraft control mode.

The motor has the following key words: the outer rotorfractional slot, concentrated winding,

permanent magnet synchronous motor.

Brushless motor parameters and characteristics

1.Size

We choose a brushless motor, you will see a lot of similar named models, such as 2216,2814, the figure, the first two is the stator diameter (mm), the latter two are the stator height (mm). The more the outer diameter and height of the stator, the larger the iron core of the stator, the more the number of turns of the coil is wound, and the greater the power of the motor is. Of course, the bigger the size, the bigger the power, but the bigger the weight.

If a motor is 2216, said the stator diameter is 22mm, the stator height is 16mm. The outside diameter of the stator and the height of the stator are proportional to the power of the motor. The height of the stator of the 2218 motor is higher than that of the 2212 motor, and certainly the power is also large. The significance of this size is to look at the model can compare the size of the two motors, but this is generally only the same stator diameter and height are not the same, or the same height and outside diameter is not the same, the stator diameter and height are different Difficult to compare this model.

It should be noted that this size refers to the stator, not referring to the motor size, the thickness of the motor shell, cooling bad, the base height affect the motor size, so use the stator size to determine the power than with the appearance Size to standard and fly.

2.Motor slot number and pole number

1) Number of slots (N): Number of slots in the stator core. Brushless motors are three-phase motors, so the slot number is a multiple of three.

2) the number of poles (P): the number of magnets on the stator, the magnet must be paired with the North and South poles, the number of poles must be even.

Motor slot number and pole number Some models of the motor directly write the number of slots N pole P, such as 12P14N, is 12 slots 14 pole meaning.

3) Slot number and pole number characteristics

a, the number of slots (N) and the number of poles (P) are inversely proportional to the higher maximum speed, that is, the smaller the number of slots (poles), the higher the best speed of the motor. Such as 9N12P highest speed than 12N14 high.

b, in the case of the same number of slots (N), the number of poles (P) is proportional to the torque, the greater the number of poles, the greater the torque.

c, under normal circumstances, the greater the number of slots (N) and the number of poles (P), the smaller the motor frustration (when the motor is not charged, hand motor rotation, will feel the feeling of a card a card frustration), theory Vibration on the motor will be less, but because it is difficult to balance the number of slots.

3, KV

The brushless motor KV value is defined as speed / V, which means an increase of 1 volt (V) to the input voltage, an increased speed of the brushless motor at idle speed (rpm). From this definition, the voltage and the motor idling speed follow a strictly linear proportional relationship and are constant regardless of the motor's compliance with that operating voltage, voltage and speed.

1) Calculation of idle speed

Remember, this value refers to the motor idling without propeller and other load speed under the relationship between the voltage, such as KV is 650, at 11.1V voltage idle speed is 11.1 × 650 = 7215 rev / min, KV value is 900, the same The idle speed at voltage is 9990 rpm.

2) The relative value of the KV value of the relative comparison (only the same stator diameter and stator height of the same model, different KV value is not much meaning, such as a certain brand of 2216 motor, 650KV, 800KV, 900KV three models )

High KV Low KV

Stator coil winding turns less

The maximum output current is small

The same voltage torque small big

Under the same voltage speed level

Matching propeller diameter small

3) can not compare the motor by KV is good or bad, can not say KV380 better than KV600, the same model with different KV value of the motor price is the same.

4. the outer rotor and inner rotor

Brushless motor according to the location of the stator can be divided into two kinds of outer rotor and inner rotor.

1) Outer rotor: The stator is inside, and the rotor is called outside rotor.

The figure is a typical external rotor motor, the rotor is surrounded by a stator, the rotor and the shell together, when rotated, the shell (excluding the base) and the output shaft together. Internal rotor torque is relatively large, KV value is low.

2) Inner rotor

In contrast to the outer rotor, the inner rotor is the stator wrapped rotor, rotating, just the rotor rotation (shell does not turn). Inner rotor torque is relatively small, KV value is high.