What to pay attention to when choosing a brushless DC motor

Date:2018-03-31 Author: Click:

Many people who use brushless motors for the first time are confused about what type of brushless motor they choose. Choosing a suitable brushless motor requires a comprehensive evaluation of the product's performance, price, and other parameters. The principle of selection of parts and raw materials for any industrial product is to meet the appropriate demand at the lowest cost.

The cost of the brushless motor is mainly in the driver board, so the single-phase price is much lower than the three-phase one. The outer rotor brushless motor is only so cheap, mainly the outer rotor motor can use single-phase drive. The advantage of a single phase is its low price. The disadvantage is its low torque and low power. The single-phase outer rotor must achieve the same three-phase torque, and the size of the motor must be large. Some applications where the torque is not demanding, such as driving blades, etc., the external rotor is sufficient.

The inner rotor brushless motor has a high price, its speed is fast, and its torque is large. For example, the brushless motor of a car vacuum cleaner uses an inner rotor, and its rotation speed is as high as more than 30,000 revolutions! The inner rotor is usually three-phase, but the inner rotor has a low productivity, the inner rotor winding method is more complicated than the outer rotor, the production capacity is much lower, and the mass production test the production capacity of the factory. Inner rotor brushless motors are generally priced at several tens of yuan each, and the prices for large power are higher. Generally, high-end applications can be used.

Let's talk about brushless geared motors. Brushless motors are currently dominated by low power, and high-power brushless motors exceeding 1 kW are expensive. Therefore, under the conditions of high torque, common brushless motors are usually added to the use of a gear box. At this time, the gear box becomes a short board. A gearbox with good performance, such as a planetary gearbox, is expensive, and its life can reach 8,000 hours, while the ordinary gearbox is low in price, but its life is only 2000 hours. The notion that brushless geared motors have a lifetime of up to tens of thousands of hours ignores the shortcomings of the gearboxes. The price of a brush motor with a reduction gear is usually only a dozen yuan, but the service life is only a few tens of hours to hundreds of hours. Brushless motor with planetary gear box, the price of one hundred and one hundred tens of dollars, the service life increased by more than ten times, but the cost has increased tenfold! The price of a planetary gear box should be more than 60 yuan. With brushless motors equipped with ordinary gearbox, the price is significantly lower, but personally feel a bit wasted motor performance.

For a very low rotational speed and precise control of rotation, ordinary brushless motors are not recommended. In this case, stepping motors can be used. Stepper motors are a type of brushless motor and also require driving. Miniature stepping motors are low in price, but their torque is also low. Of course, the angle of rotation can be precisely controlled. A micro stepper motor is usually used with a reduction gear box because the torque is too low. High-power stepper motors are expensive.

For aeromodelling motors that require a small motor and a large amount of power for a short time, it is necessary to use a model aircraft motor. The cost of aeromodelling motors is quite high, mainly because their shells are machined in the yard, and the magnets they use are not ordinary ferrites but high-priced neodymium-iron neodymium magnets. As long as the cost is not taken into consideration, ordinary motors with strong magnets perform as well.

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