As we have learned, the role of the ESC is to deliver electrical energy from the battery to the motor in a controlled manner. If you put 50% throttle on the controller, the ESC will give the motor 50% "power". What is "powered" depends on the firmware it uses. Some devices get the average voltage sent to the motor, some target RPM, and some use a mix of both.
One end of the ESC has two wires that connect to the battery, a red (positive) wire and a black (negative) wire, while the other end has three wires that connect the ESC to the brushless motor. If the rotation direction of the motor is wrong after connecting to the ESC, switching any two wires will make it rotate in the correct direction. Finally, the ESC extension is connected to the throttle receiver powered by the BEC.
There are two components inside a brushless motor: the rotor (containing the permanent magnets) and the stator (containing the copper coils). When current is passed to the coils of the stator, it becomes an electromagnet and forms a north and south pole. When the polarity of the electromagnet is matched with the polarity of the permanent magnet it faces, the rotor spins because of the same-sex repulsion. The current is supplied by the ESC in the form of a three-phase signal and constantly changes the polarity of the electromagnets, which keeps the rotor spinning all the time.
In order to complete the above activation process, the ESC needs to know the rotor position in advance in order to determine which electromagnets to select to activate. The ESC uses Hall-effect sensors to determine the position of the rotor in the sensor motor, and the sensor information is output in phase and precisely synchronized with the angle of the rotor to ensure smooth acceleration of the rotor. In motors without sensors (more commonly used in drones), the starting process is slightly less stable. The ESC will send a predetermined sequence to the motor to start it. As long as the motor has sufficient speed, the back electromagnetic force (back EMF) is sufficient to allow the ESC to obtain an estimated precise position and synchronize with the signal pulse.
【Introduction to drone ESC and how to choose a suitable ESC? 】
Choosing an ESC is an important part of the drone design process. You want to make sure that it meets your aircraft's power needs without overly draining your battery. Here are a few factors to consider when choosing an ESC.
(1) ESC current rating
The rated current of the ESC should be 10-20% higher than the rated current of the motor. This will keep it from overheating and give a little wiggle room when running at max throttle. You don't want to go above this range to minimize weight. ESCs should be tested in flight-like conditions, as the main limitation is heat. High temperatures and low air circulation can degrade ESC ratings and life. Some ESCs have two current ratings: continuous and burst. Continuous current can last for a long time, while burst current can only last for a short time.
(2) ESC voltage
ESC has a maximum voltage limit which can be given as voltage range or battery range. For example, an ESC rated for a 3S-8S battery will support 11.1-33.6V. ESC allows you to set a shutdown voltage that will alert you when the battery voltage becomes too low (3.0-3.4V per battery) to avoid damaging the battery. These systems are called Low Voltage Cutouts (LVC), and they reduce the maximum power the ESC can deliver. Eventually, the ESC will turn off the motor.
(3) 4-in-1 ESC for quadcopter
When connecting an ESC to a quadcopter, you can have one ESC per motor, or use a 4-in-1 ESC with a single board and four motor connectors. If the motor has high power draw, having four ECS can help spread the thermal load, and the 4-in-1 ESC is a great option to save space and limit the weight of your hardware.