An ESC (acronym for “Electronic Speed Controller“) is what allows the flight controller (covered in the next lesson) to control the speed and direction of a motor. The ESC must be able to handle the maximum current which the motor might consume, and be able to provide it at the right voltage. Most ESCs used in the hobby industry only allow the motor to rotate in one direction, though with the right firmware, they can operate in both directions.


An ESC might initially be confusing because it has several wires exiting on two sides.

  • Power input: The two thick wires (normally black and red) are to obtain power from the power distribution board / harness which itself receives power directly from the main battery.
  • 3 bullet connectors: These pins are what connects to the three pins on the brushless motor. There are some standard sizes in the industry, but if you find the two are mismatched, you will need to replace one set.
  • 3-pin R/C servo connector: This connector accepts RC signals, but rather than requiring 5V on the red and black pins, most of the time an internal BEC provides 5V to power the electronics.

In certain instances, the manufacturer does not want to assume which connectors you are using, and leaves the wires for the motor connection and power input bare (they may provide bullet connectors in the packaging which you may or may not want/need and would have to solder onto the wires). The bullet connectors you received with the motors may also not match those of the ESC, so in this case, it’s simply best to replace one or the other. Your next question is obviously given three bullet connectors, which one plugs into which on the motor? As far as the connector for the power, this is entirely up to you – ideally you would use connectors to make the ESC easily removable in case of failure, or if you want to use it on a different project, but be sure that the positive on the ESC goes to the positive on the battery, and same for negative. In order to reverse the direction of rotation, swap any of two of the three connectors between the ESC and the brushless motor.


Most ESCs include what is called a “Battery Elimination Circuit” or BEC. This comes from the fact that historically, only one brushless motor was needed in a given RC vehicle, and rather than splitting hte battery, it would just need to be connected to the ESC, and the ESC would have an onboard voltage regulator to power the electronics.It is important to know the current which an ESC’s BEC can provide, though it is normally in the range of 1A or above and is almost always 5V.

In a multi-rotor, you need to connect four or more ESCs to the flight controller, but only one ESC is needed, and having power coming from multiple sources all being fed to the same lines can potentially cause issues. Since there is normally no way to deactivate a BEC on an ESC, it is best to remove the red wire and wrap it with electrical tape for all but one ESC. It is still important to leave the black (ground) wire in place for “common ground”.


ESCs are not all equally good for use with multi-rotors. It is important to understand that before multi-rotors were around, that brushelss hobby motors were used primarily for RC car drives, airplane propellers and as primary motors in model helicopters. Most of these applications did not require very fast response time or rapid updating. An ESC equipped with SimonK or bheli firmware is able to react very fast (much higher frequency) to changes in input, which may mean the different between stable flight or a crash.

Power Distribution

Since each ESC is powered from the main battery, the main battery’s single connector must somehow be split amongst four ESCs. To do so, a power distribution board, or power distribution harness is used. This board (or cable) splits the main battery’s positive and negative terminals into four. It is important to note the type of connectors used on the battery, ESC and power distribution board may not all be the same, and it is best, whenever possible, to choose a “standard” connector (such as Deans) which is used throughout. Many inexpensive boards require soldering, as they do not want to assume you are using any specific connector. A very simply power distributor could involve a two input terminal block or soldering all positive connections together, and then all negative connections together..



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