How a brushless motor works. Why are its dimensions smaller and the cost higher than the brush counterparts?

Brushless motors have long been installed in power tools. Such electric motors have a number of advantages over collector motors (I will list below). But there is one big drawback - the high price. What is it all connected with? I propose to figure it out.

If we open the cordless screwdrivers from two types of electric motors, we will immediately see that the brushless, with the same characteristics (or even better), has smaller dimensions:

This is understandable, since it has no brushes - contacts that transmit voltage to the winding. Although this is still the same permanent magnet electric motor, the magnets are located on the rotor (rotate), and the coil windings are stationary:

There are several types of brushless electric motors: with an internal winding and an internal rotor on permanent magnets (photos 1 and 2) and with an outer winding and an inner rotor with magnets (photo 3). They are also divided into synchronous and asynchronous (with synchronization of the rotor-stator magnetic fields and ahead of the magnetic field on the stator).

The electric motor switches the magnetic field (supply of the coils). By the principle of attraction of different poles of a magnet. At a certain moment, the desired coil must be attracted to the opposite pole of the permanent magnet. In the collector, switching is made constructively due to sliding contacts. And if there are no sliding contacts in a brushless one - how to understand which coil to apply voltage to? And how does this switch take place?

Hall sensors are installed on the coils to control the position of the rotor:

Hall sensor working principle:

They give a signal to the control unit (controller) and that supplies voltage to the desired stator winding. It looks like this when rotating:

The rotor catches up with the stator magnetic field. Example of a motor control board:

How a brushless electric motor works and works in an accessible language is described in this video:

It can be seen that they are half or even twice as high as their brush counterparts.

It is clear that the electronic part is difficult to manufacture and has an additional cost in the total cost of the electric motor for any tool. But the advantages of such an electric motor are a significant list:

1. Because a collector motor above 3000 rpm reduces its power and efficiency, the contact in the brushes is broken, and sparking appears. Brushless motors are free of these disadvantages and have a stable efficiency of up to 90% at all speeds. They are mechanically more durable (the resource depends only on the bearings). May have higher revs.

2. The brushless motor makes it easier to adjust the (electronic) torque. Usually, a switch is installed on brushless screwdrivers, which is responsible for this. Due to the increased efficiency, brushless electric motors save the battery charge of the tool, some are up to 50% more economical than collector motors.

But if the electronic part of the electric motor control fails, then the repair can be comparable in cost to a new tool. Electronics always have a risk of breakage. Short circuits in the event of moisture or the effect of electrostatics on Hall sensors and microcircuits - no one is immune from this.

Despite these risks, these engines are the future. Because their characteristics are higher than collector ones. Perhaps someday the industry will begin to produce control units in one microcircuit case with reliable protection against short circuits and static electricity.

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