Electronics and Propulsion System in RC Flying - Part 3 - ESC

3. Electronic Speed Controller (ESC)
An electronic speed control or ESC is an electronic circuit used for controlling brushless motor's speed, its direction of rotation and also used as a dynamic brake. ESCs are used on electrically powered radio controlled models.

The ESC (Electronic Speed Controller) has three main functions.
  1. It converts the battery voltage to a safe 5v for the receiver  and servos to run on.
  2. ESC controls the motor speed based on throttle signal sent from the receiver.
  3. It converts the battery's direct current (DC) into alternating current (AC) that is required by the brushless motor.








  • The selection of ESC is based on the maximum current consumption of the motor you are going to use, ESC's comes in different ampere ratings.
  • ESCs will also show whether they are for brushed motors or brushless motors.
  • The motors we use in our RC planes are brushless.
  • ESCs are programmable too. The programmable features are  motor starts , helicopter mode, timing, cut off voltage , etc.
  • Programming can be done with Tx-Rx or with the help of ESC Programming cards.
  • Procedure for programming will be given in the ESC manual.
  • ESCs are normally rated according to maximum current they can handle safely, for example,  a 30A ESC can handle 30 amperes current continuously.
  • Generally the higher the rating, the larger and heavier the ESC .
  • Working of ESC is based on Pulse Width Modulation (PWM).
  • Which means that the motor's rpm is regulated by varying the pulses duty-cycle according to the transmitter's throttle position. ( We will learn this in detail in BLDC motor section).
  • Most ESCs have a facility known as Battery Eliminator Circuit (BEC).
  • These BEC include a 5V regulator to supply the receiver and servos from the same battery that is used to power the motor, thereby eliminating the weight of a second battery only to power the radio and servos.
  • ESCs without BEC is called OPTO ESC.
  • Most of the ESC has a programmable function to cut-off  motor power when the battery voltage falls to a preset value, for example 3 V/cell.
  • This prevents the battery from getting totally drain out same time giving power to servos and Rx allowing the pilot to control the model when the motor stops.
  • Most of the ESCs have programmable functions, such as battery selection, cut off voltage, brake, motor direction, etc..
  • Electronic Speed Controllers are available in different sizes and weights, which depends on their max output current capabilities.
ESC – Manufactures Data
Example 1 - TURNIGY Plush 60amp Speed Controller
Cont Current: 60A    Burst Current: 80A
BEC Mode: Switching     BEC : 5v / 3A
Input: 5.6v-22v    Weight: 60g
Size: 80x31x14mm

Example 2 - HobbyWing X-Rotor 20A OPTO ESC for Multirotor Applications
Specs:  Amps: 20A   Max Peak Amps: 30A for 10s
BEC: No (OPTO)
Cells: 2-4S   Timing: High/Intermediate
Weight: 14g  Size: 52x31x7mm   Connectors: 3.5mm bullet
Programming Functions: ESC
Battery Type: Lipo /NiXX
Brake: On / Off
Voltage Protection: Low / Mid / High
Protection mode: Reduce power / Cut off power
Timing: Auto / High / Low
Startup: Fast / Normal / Soft
PWM Frequency: 8k / 16k
Helicopter mode: Off / 5sec / 15sec (Start up delay)
How to select proper ESC for your model.
  1. ESC selection mainly depends upon the maximum current consumption and maximum working voltage of your motor.
  2. If the selected motor has a max current consumption of 20 amps and max working voltage of 4 cell Lippo (14.8V), then the required ESC will be minimum of 20A, 2-4cells. 
  3. You can go for higher Amps and cell count (which will give you a safe margin, ESCs heat up during operation, higher Amps ESC will have more heat dissipation, moreover the same ESC can be used with other motors also) keeping the weight and cost in mind.
  4. You cannot use 15A, 3cell ESC for a motor having 25A , 4cell count, but you can use a 30A 6 cell ESC for the same motor.
  5. Be careful to find out whether the ESC is OPTO or with BEC. ( If seyou lect OPTO ESC then you have to provide separate power supply for your RX and Servos).
  6. There are two types of BEC - linear and switching. 
  7. Linear BEC gives out a constant out put irrespective of the load, means more battery drain and chances of burnouts, but Switching BEC gives output as per the load requirement.
  8. Again carefully read the manufactures data and do comparison, decide upon the cost and weight.( for RC-Aircraft savings on weight is an important factor, as Amp capacity goes up weight and cost also goes up).
  9.  One more important thing to look in to is the programmable functions avialiable with ESC (many times you have to use this functions). 
  10. After carefully going through all the above mentioned details finally select the ESC as per your budget. 
ESC Programming Card.