There is also a "power system" throughout the quadcopter (or other multicopter). This "power system" consists of ESCs, motors and paddles. In this section, you will learn how to choose a quadcopter "power system" according to your needs. The basis of making a drone is a brushless motor. To make the whole drone hover in the air, the combination of motor and propeller is necessary. To make a drone fly as long as possible, a balance needs to be found between the motors, propellers and the weight of the entire structure. Like all electric motors, a brushless motor consists of bearings, coils, magnets (neodymium magnets for smaller motors, electromagnets for larger motors), and a stator and endshields connected by bearings, as shown. The part on the left in the figure includes the coil core, the coil and the ball bearing, and the part on the right includes the permanent magnet and the rotating shaft placed in the bearing.The important characteristics of brushless motors are KV value, weight, no-load current, maximum current and maximum voltage that can be carried. The brushed motor rotates by obtaining the force of the magnetic field in a fixed direction through the structural design of the brushes and the commutator. The brushless motor has no brushes and commutators. How does it obtain the magnetic field force in a fixed direction? Simply put, by changing the alternating frequency and waveform of the current wave input to the stator coil of the brushless motor, the winding coil A magnetic field that rotates around the geometric axis of the motor is formed around it. This magnetic field drives the permanent magnet steel on the rotor to rotate, and the motor starts to rotate. The diagram below depicts a typical duty cycle of a three-phase brushless motor. To make the motor rotate, it is necessary to use the electronic governor to make the three-phase direct current appear alternately. Each phase sequentially changes switching state over time. Three AC brushless motor working cycle process Why do most drones use brushless motors? This kind of motor has less friction and lower loss than brushed motors. Compared with brushed motors, brushless motors generate less heat, have a longer life, lower noise, operate more comfortably, and have lower maintenance costs. One of the most important parameters of the brushless motor is the KV value, which is a unique performance parameter of the brushless motor and an important data for judging the performance characteristics of the brushless motor. 1. The KV value of the brushless motor is defined as speed/volt, which means that the input voltage increases by 1 volt, and the speed value of the idling speed of the brushless motor increases (rev/min) 2. From this definition, we can know that the input of the brushless motor voltage and the idling speed of the motor follow a strict linear proportional relationship. For example: the KV value of a brushless motor is 1000KV, which means that the motor rotates at 1000 revolutions per minute under 1V voltage. Then under 10V voltage, the motor speed is: 10V1000KV=10000 rpm, of course, these are when the motor is no-load. 3. The four digits on the motor, the first two digits represent the diameter of the motor stator, in millimeters. The last two digits represent the height of the motor stator, which is also in millimeters. For example: 2212. It means that the diameter of the stator of this motor is 22 mm, and the height of the stator is 12 mm. 4. Some motors also have a parameter such as: 12T, 8T. This T represents the number of coils of the motor, also called the number of turns. 5. For the same motor, the number of winding turns is large, the KV value is low, the maximum output current is small, but the torque is large, and the shape of the motor is flat and thick. 6. For the same motor, the number of winding turns is small, the KV value is high, the maximum output current is large, but the torque is small, and the shape of the motor is thin and tall. These parameters on the UAV motor can let us know the performance and purpose of this motor at a glance.
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