The basic principle of micro motor rotation
Figure 1 State: When the coils at both ends are energized, according to the right-hand screw rule, an applied magnetic induction intensity B (as shown in the direction of the thick arrow) will be generated pointing to the right, and the rotor in the middle will try to make its own internal magnetic induction intensity. The line direction is consistent with the direction of the outer magnetic field line to form a shortest closed magnetic field line loop, so that the inner rotor will rotate clockwise;
When the direction of the rotor magnetic field is perpendicular to the direction of the external magnetic field, the rotational torque of the rotor is the largest. Note that the "moment" is said to be the largest, not the "force". It is true that when the rotor magnetic field is in the same direction as the external magnetic field, the magnetic force on the rotor is the largest, but at this time the rotor is in a horizontal state and the force arm is 0, and of course it will not rotate. The moment is the product of the force and the force arm. One of them is zero, and the product is zero. When the rotor turns to the horizontal position, although it is no longer affected by the rotational torque, it will continue to rotate clockwise due to inertia. At this time, if the current of the two solenoids is changed direction, as shown, the rotor will continue to rotate forward clockwise.
Figure ② Status: Constantly changing the current direction of the two solenoids, the inner rotor will keep rotating. This action of changing the direction of the current is called commutation (when the commutation is only related to the position of the rotor and not directly related to any other quantity).
Brushless Micro DC Motor Parameters
1) Rated voltage: that is, a suitable working motor for a micro motor, there are many suitable working motors for a micro motor, and the rated voltage is obtained by specifying the load conditions;
2) KV value: The rated speed of the micro brush motor is marked according to the rated working voltage. The concept of KV value of the brushless motor allows users to intuitively understand the speed of the micro brushless motor under the specific working voltage (actual speed = KV value × Operating Voltage);
3) Torque: The rotor of the micro motor generates a driving torque that can be used to drive the mechanical load, that is, the rotational force of the micro motor;
4) Speed: that is, the speed of the micro motor per minute;
5) Maximum current: the maximum current that the micro motor can withstand and work safely;
6) Maximum power: the maximum power that the micro motor can withstand and work safely (power = voltage × current);
Micro Brushless Motor Power and Efficiency
The output power of the micro motor = speed × torque. Under the same power, the relationship between torque and speed is trade-off, that is, the higher the speed of the micro motor, the lower the torque, and the lower the speed, the higher the torque , this rule is used for all micro motors. The micro motor has its own torque on the line, and the maximum power is the upper limit. If the maximum power is exceeded, the micro motor will be burned. The maximum power is also obtained under the specified working voltage. , If the working voltage is higher, the maximum power will also increase. The formula Q=I2R The heating of the conductor is proportional to the square of the current. At a higher voltage, if it is the same power, the current will decrease and the heating will decrease. , so that the maximum power increases.
Relationship between Voltage and Efficiency of Brushless Micromotors
1) Power = voltage × current;
2) Heating value = square of current × resistance.
Two conclusions are drawn from the formula: under the same power, the higher the voltage, the smaller the current, and it is deduced that: under the same power, the higher the voltage, the smaller the calorific value.
The number of pole pairs of the micro motor: the rotation speed of the magnetic field is also called the synchronous speed, which is related to the frequency of the three-phase current and the number of pole pairs p. If the stator winding has only one pair of magnetic poles at any time (the number of pole pairs p=1), that is, there are only two magnetic poles, for the rotating magnetic field with only one pair of magnetic poles, the three-phase current changes once, and the combined magnetic field also changes with For one rotation, if it is an alternating current of 50hz, the synchronous speed of the rotating magnetic field is 50 rpm or 3000 rpm. In engineering technology, r/min is often used to represent the speed. If the magnetic field synthesized by the stator winding has two pairs of magnetic poles (the number of pole pairs p=2), that is, there are four magnetic poles, it can be proved that the current changes for one cycle, and the synthesized magnetic field rotates 180 degrees in space. The synchronous speed of the rotating magnetic field per minute is n=60f/p. When the number of pole pairs is constant, if the frequency of the alternating current is changed, the synchronous speed of the rotating magnetic field can be changed, which is the basic principle of variable frequency speed regulation. Since the magnetic poles of the motor appear in pairs, they are also often represented by pole pairs;
Magnets for Micro Brushless Motors: NdFeB magnets are 3 times more magnetic than the black ferrite magnets commonly found in our lives! Of course, the price is more than 10 times that of ferrite magnets. Brushless motors are finally classified as permanent magnet motors, and the power and characteristics of permanent magnet motors are completely dependent on magnets. Basically, it can be said that the size of the magnet determines the maximum power of the micro motor;
Silicon steel sheet of micro DC motor: air is weakly magnetically conductive, but iron is magnetically conductive. The function of silicon steel sheet is to guide the magnetic circuit of the magnet and form a loop, which requires motor reluctance (understood as resistance) smaller.
