Basic Components of Multi-rotor Drones: Brushless Motors
There is also a power system in the entire quad-copter (or other multi-copter). This power system consists of an ESC, a motor and a blade. Here, you will learn how to choose a power system for a quad-copter according to your needs.
The basis of making drones is brushless motors. To make the entire drone hover in the air, a combination of motor and propeller is necessary. To make the UAV’s flight time as long as possible, it is necessary to find a balance between the weight of the motor, the propeller and the entire structure. Like all motors, brushless motors include bearings, coils, magnets (neodymium magnets for small motors, electromagnets for large motors), as well as stators and end covers connected by bearings, as shown in the following picture.
The left part of the picture includes the coil core, coil and ball bearing, and the right part includes the permanent magnet and the rotating shaft placed in the bearing.
There are several data of brushless motors that need to be payed attention to, namely KV value, weight, no-load current, maximum current and maximum voltage that can be carried.
The brushed motor is rotated by obtaining a fixed direction of the magnetic field force through the structural design of the brush and the inverter. The brushless motor has no brushes and inverters. How does it obtain the force of the magnetic field in a fixed direction? In short, by changing the alternating frequency and waveform of the current wave input to the stator coil of the brushless motor, a magnetic field rotating around the geometric axis of the motor is formed around the winding coil. This magnetic field drives the permanent magnet on the rotor to rotate. Then the motor will spin up.
The following picture describes the typical working cycle of a three-phase brushless motor. To make the motor rotate, it is necessary to use an electronic governor to make the three-phase direct current alternately appear. Each phase changes the switch state in turn over time.
Why do most drones use brushless motors? This kind of motor has lower friction and lower loss than brushed motors. Moreover, the brushless motor has low heat generation, long service life, low noise, smooth operation, and lower maintenance costs.
The most important parameter of a brushless motor is the KV value. This value is a unique performance parameter of a brushless motor and an important data for judging the performance characteristics of a brushless motor.
1.The KV value of the brushless motor is defined as speed/volt, which means the speed value (rev/min) at which the idling speed of the brushless motor increases by 1 volt when the input voltage is increased.
2.From this definition, we can know that the voltage input of the brushless motor and the motor idling speed 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 at a voltage of 1V. Under 10V voltage, the motor speed is: 10V*1000KV=10000 rpm, of course these are all when the motor is unloaded.
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, and the height is also millimeters.
For example, 2212 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 parameters, such as: 12T, 8T. This T represents the number of winding of the motor, also called the number of turns.
5.The same motor, with a large number of winding turns, has a low KV value and a small maximum output current, but the torque is large and the motor shape is flat and thick.
6.For the same motor, the number of winding turns is small, the KV value is high, and the highest output current is also large, but the torque is small, and the motor shape is thin and tall.
These parameters on the drone motor allow us to understand the performance and purpose of the motor at a glance.