Main parameters and selection of brushless motor

Main parameters and selection of brushless motor

The main parameters and selection of brushless motor are as follows:

1. Motor model: such as 2212, 3508 and 4010. These numbers respectively represent the diameter and height of the motor stator, and the unit is millimeters. The larger the first two digits, the larger the motor diameter and torque; The larger the last two digits, the higher the motor, the better the balance. Fat and tall motors have high torque, high efficiency and high price.

2. Motor KV value: KV value refers to the number of idling revolutions per minute of the motor for every increase of 1V voltage. For example, 1000KV means that the idling speed is 1000 rpm at 1V, and the idling speed is 10000KV rpm at 10V.

So what determines the value of KV? This is related to the number of winding turns of the motor. The motor with more winding turns has low KV value, large torque and high maximum output current. Under the same voltage, the smaller the KV value, the lower the revolution, and the greater the torque, the more slurry can be carried. The larger the KV value, the higher the rotation speed and the smaller the torque.

Relatively speaking, the smaller the KV value, the higher the efficiency. For example, aerial photography should use a low KV motor with large slurry. Because the lower the speed of the motor, the higher the efficiency, and the smaller the vibration of the low-speed motor, these factors are extremely beneficial to aerial photography.

Brushless motors used in airplane models are mainly divided into three categories: high kV (above 2000 kV), medium KV(700KV~1500KV) and low KV(100KV~500KV). The fixed wing and crossing machine generally use high KV motors; Small wheelbase aerial cameras generally use medium or low KV motors; Unmanned aerial vehicles with heavy weight, heavy load, large load and large wheelbase generally choose low KV motors.

3. Motor efficiency: Motor efficiency refers to the ratio of electric energy consumed by the motor to mechanical kinetic energy, and the marking method of brushless motor efficiency is gW (g/watt).

First of all, we should know that the power and tension of the motor are not simple multiples. For example:

When the motor works at 50W, it produces 450g tensile force, but when the motor works at 100W, it does not.

900 tension, may only reach 700g tension, the actual tension depends on the efficiency table equipped with the motor. Most motors have the highest efficiency when working at the current of 3A~8A.

Take Langyu X3508S-700KV motor as an example. When equipped with APC1147 paddle, 4S battery and 5A current, the thrust is 600g and the efficiency is 8.1gW；. If it is a 4-axis aircraft, multiply the thrust of a single motor by 4, which results in a total thrust of 24kg.