Complete Knowlege for Brushless Motor 4
Part IV: External Rotor Brushless DC Motor
After reading the structure of the inner rotor brushless DC motor, we look at the outer rotor. The difference is that the outer rotor motor will make a piece of magnetic steel originally located at the center and stick to the shell. When the motor is running, the whole shell is rotating, and the stator of the middle coil is not moving. The outer rotor brushless DC motor is much larger than the inner rotor, and the rotor's moment of inertia is much larger (because the main mass of the rotor is concentrated on the housing), so the speed is slower than that of the inner rotor motor, and the KV value is usually several hundred to several thousand. between. It is also a brushless motor mainly used by model airplanes.
By the way, take a look. The KV value of a brushless motor is defined as: speed/V, which means that for every 1 volt increase in the input voltage, the speed at which the brushless motor idling speed increases. For example, for an external rotor brushless motor with a nominal value of 1000 kV, the maximum no-load speed under the condition of 11 volts is: 11,000 rpm (rpm means: rpm). Brushless motors of the same size and size in the same series exhibit different KV characteristics depending on the number of winding turns. With many winding turns, the KV value is low, the maximum output current is small, and the torque is large; the winding number is small, the KV value is high, the maximum output current is large, and the torque is small. I have previously tested the limiting current through the machine's 2204 motor. The single motor can hit 25A and the 2212 motor 15A cannot.
External rotor brushless DC motor structure:
The analysis method is similar to that of the inner rotor motor. Everybody can analyze it by yourself. According to the right hand helix theorem, judge the N/S pole of the coil, the N pole of the rotor permanent magnet and the S pole of the stator winding have the tendency of alignment (attraction), the rotor permanent magnet The S pole has a tendency to align (attract) the N pole of the stator windings, thereby driving the motor to rotate.
Analysis of Structure of Classic Brushless Motor 2212 1000kv.
The picture shows the DJI 2312S motor and XXD 2212 motor (anatomy) Its structure is as follows: The stator winding is fixed on the base, the rotating shaft and the shell are fixed together to form a rotor, and the bearing in the middle of the stator is inserted.
The picture shows the xxd2212 coil dismantling
The picture shows the 12 windings of 14 poles (ie 7 pairs of poles), motor winding winding diagram. Later, six types of two-phase energization conditions are shown. It can be seen that although the number of windings and magnetic poles can vary in many ways, the order of energization is actually the same from the viewpoint of electrical control. That is to say, The outer rotor or the inner rotor motor both follow the order of AB->AC->BC->BA->CA->CB. Of course, if you want to reverse the motor, the electronic method is to power up in reverse order; the physical method directly swaps any two lines, assuming A and B are reversed, then the order is BA->BC->AC->AB- >CB->CA, did you find that the order was completely reversed?
AB phase power
AC phase power
BC phase power
BA PHASE POWER
CA PHASE POWER
To illustrate, since each lead connects two windings at the same time, the current is divided in two. Here, in order to make the problem as simple as possible, only the current direction of the main circuit is drawn in the following figures, and the current of one circuit is not drawn. The specific condition of the other circuit is placed behind the analysis and involves the circuit detecting the commutation position. .
With love
www.vibrationmotor.net
Specialist for micro DC motor which can be used for drone