As shown in Figure 1, this is a DC brush motor structure model diagram. Two fixed opposite magnets, a coil is placed in the middle, the two ends of the coil are respectively connected to two semicircular copper rings, the two ends of the copper ring are in contact with the fixed carbon brush, and then the two ends of the carbon brush are respectively connected to the DC power supply.

Figure 1

After the power is connected, the current is shown by the arrow in Figure 1. According to the left-hand definition, the yellow coil is subjected to a vertical upward electromagnetic force; the blue coil is subjected to a vertical downward electromagnetic force. The motor rotor starts to rotate clockwise, after rotating 90 degrees, as shown in Figure 2:

Figure 2

At this time, the carbon brush is just in the gap between the two copper rings, and the whole coil circuit has no current. But under the action of inertia, the rotor still continues to rotate.

Figure 3

When the rotor turns to the above position under the action of inertia, the coil current is shown in Figure 3. According to the left-handed definition, the blue coil is subjected to a vertical upward electromagnetic force; the yellow coil is subjected to a vertical downward electromagnetic force. The rotor of the motor continues to rotate clockwise and rotates 90 degrees. At this time, the carbon brush is just in the gap between the two copper rings, and the whole coil circuit has no current. But under the action of inertia, the rotor still continues to rotate. Then repeat the above steps and keep the cycle going.

DC brushless motor

As shown in Figure 5, this is a DC brushless motor structure model diagram. It is composed of two parts: a stator and a rotor. The rotor has a pair of magnetic poles; there are many sets of coils wound on the stator. There are 6 sets of coils in the picture.

Figure 5

When we pass current to the stator coils 2 and 5, the coils 2 and 5 will generate magnetic fields. The stator is equivalent to a bar magnet, where 2 is the S (south) pole and 5 is the N (north) pole. Since the same-sex poles attract each other, the rotor N pole will rotate to the coil 2 position and the rotor S pole will rotate to the coil 5 position, Figure 6.

Figure 6

Then we remove the current from the stator coils 2 and 5, and then supply current to the stator coils 3 and 6. At this time, coils 3 and 6 will generate magnetic fields, and the stator is equivalent to a bar magnet, of which 3 is S (south) pole and 6 is N (north) pole. Since the same-sex poles attract each other, the rotor N pole will rotate to the coil 3 position and the rotor S pole will rotate to the coil 6 position, Figure 7.

Figure 7

Similarly, remove the current of stator coils 3 and 6, and then apply current to stator coils 4 and 1. At this time, coils 4 and 1 will generate a magnetic field, and the stator is equivalent to a bar magnet, of which 4 is S (south) pole and 1 is N (north) pole. Since the different magnetic poles attract each other, the rotor N pole will rotate to the coil 4 position, and the rotor S pole will rotate to the coil 1 position.

At this point, the motor has rotated half a turn .... The second half of the turn is consistent with the previous principle, so I won't repeat it here. We can simply think of a brushless DC motor as, like fishing for a carrot in front of a donkey, so that the donkey will always move towards the carrot.

 

How can we pass accurate current to different coils at different times? This requires a current commutation circuit... It will not be described in detail here.

 

Comparison of both advantages and disadvantages

dc brush motor:Fast start, timely braking, stable speed regulation, simple control, simple structure and low price. The point is cheap! The price is cheap! The price is cheap! Moreover, it has a large starting current, a large torque (rotating force) at low speed, and can bring a heavy load.

However, due to the friction between the carbon brush and the commutator, the brush DC motor is prone to sparks, heat, noise, electromagnetic interference to the external environment, and has low efficiency and short life. Because the carbon brush is a wear and tear, it is easy to malfunction and needs to be replaced for a period of time.

brushless dc motor:Because the DC brushless motor eliminates the carbon brush, it has low noise, no maintenance, low failure rate, long service life, stable running time and voltage, and less interference with radio equipment. But it's expensive! The price is expensive! The price is expensive!

Power tools are very commonly used tools in life. There are many types of brands and fierce competition. Everyone is very price sensitive. Moreover, electric tools need to carry a heavy load and have a large starting torque, such as hand electric drills and impact drills. Otherwise, when drilling, the motor is easy to run because the drill bit is stuck.