Essential details

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Product samples

• Brushless motor power and efficiency:

Output power=speed * torque.

Under the same power, torque and speed have a trade-off relationship, that is, the higher the speed of the same motor, the lower its torque, and vice versa. It is impossible to require a higher motor speed and torque, as this rule applies to all motors. For example, a 2212-850KV motor can drive 1045 propellers at 11V. If the voltage is doubled, the speed also doubles. If the load is still 1045 propellers at this time, the motor will quickly burn out due to a sharp increase in current and temperature.

Each motor has its own power limit, and the maximum power is this limit. If the working condition exceeds this maximum power, it will cause the motor to burn out due to high temperature. Of course, this maximum power is also determined under the specified operating voltage. If it is at a higher operating voltage, the reasonable maximum power will also be increased. Q=I2R, the heating of a conductor is proportional to the square of the current. At higher voltages, if the power is the same, the current will decrease, leading to a decrease in heating and an increase in maximum power. This also explains why 22.2V or even 30V batteries are widely used in professional aerial photography aircraft to drive Multirotor. Brushless motors under high voltage have low current, low heat and higher efficiency.

• Regarding the magnetic pole pairs of brushless motors:

The rotating speed of magnetic field is also called synchronous speed, which is related to the frequency of three-phase current and the number of magnetic poles p.

If the stator winding has only one pair of magnetic poles (the number of magnetic poles p=1) at any time, that is, only two magnetic poles. For the rotating magnetic field with only one pair of magnetic poles, the three-phase current changes once, and the synthetic magnetic field also rotates once. If it is 50 hz AC, the synchronous speed of the rotating magnetic field is 50 r/s or 3000 r/min. In engineering technology, the speed is usually expressed in revolutions per minute (r/min). If the magnetic field formed by the combination of the stator winding has two pairs of magnetic poles (magnetic pole logarithm p=2), that is, four magnetic poles, it can be proven that the current changes for one cycle, and the composite magnetic field rotates 180 degrees in space. Therefore, it can be generalized that the synchronous speed of the rotating magnetic field of p pair of magnetic poles per minute is n=60f/p.

When the number of magnetic poles is fixed, changing the frequency of alternating current can change the synchronous speed of the rotating magnetic field, which is the basic principle of variable frequency speed regulation. Due to the fact that the magnetic poles of a motor appear in pairs, they are often represented by the number of pole pairs.