You’ll see a lot of electric helicopters being advertised as having an ESC, or Electronic Speed Controller, as if it was the latest big thing. But it’s the kind of controller that makes these RC helicopters special - not the fact that it has one. All variable speed motors need an ESC, or they won’t work!
The ESC is the throttle control of RC helicopters. It is an electronic device, one side of which connects to the battery and the other side to the motor. A third lead connects to a servo channel on the receiver.
This last lead is often called the servo lead, but that’s a misnomer. What you are doing is using a spare servo channel to do another job - transfer the throttle signal from the receiver to the speed controller, so it can in turn control the speed of the motor.
Most speed controllers on electric helicopters have a BEC (battery eliminating circuit). This allows all the electronic gadgetry on board your chopper - radio receiver, servos etc - to run off just the one central battery pack. They are rated in variable amperages, anything from 5 amps (or less) to 50 plus, depending on the size of the helicopter and what equipment it has on board. It’s important that electric helicopters are equipped with the correct BEC unit for the motor and battery installed.
It is important you choose the correct ESC for the type of motor you have. With brushed motors, speed control is achieved by a simple variation of the amount of power supplied to the motor. It does this by a pulse system. Many pulses a second are delivered; the longer the pulses, the more power is delivered to the motor. ESCs connect to brushed motors with 2 wires.
With brushless motors, the same principle is used. However, to make the motor turn the controller has to select between various sets of windings. Most brushless ESCs are sensor-less speed controllers; they use the residual voltage (Back EMF) in momentarily inactive windings to decide the position of the motor, and then act accordingly.
All brushless ESCs have three wires. Really, all you need to know is that a brushed ESC cannot be connected to a brushless motor, and vice versa.