Originally Posted by Faiz
every ESC mostly consist of Mosfet IC's, Microcontroller/s, and BEC circuitry.
in automobile term, mosfet is equal to Fuel Injector, and Microcontroller is the car ECU,
mosfet is kind of on-off switch, in basic form such as IRF product, it has 3 pins : G (Gate), D (Discharge), S (Source), electric current flow in through S pin and exit through D pin, G pins control the currect flow
and driven by square pulse from on-board small programmable microcontroller,
And to elaborate, the Mosfet aplifies a signal, basically the same way a car amplifier "amplifies" the signal from the receiver.
So, the microprocessors inside the ESC get a signal from the receiver to accelerate (from your controller) and so a microprocessor sends very low current pulses to the Gate. The ammount of current never varies, nor does the frequency from the microprocessor (unless you have a variable frequency ESC - some do that in response to the load). But it does vary the ammount of time that the pulse is "ON" for each cycle. Very short on pulses give low rpm, and longer ON pulses produce higher RPM.
Motors perform much better using ESC than just a resistor type of speed control for a couple reasons. First there is very little resistance in the circuit, so you are not losing power as heat through the speed controll.
Secondly, even at low speed (short pulses) the motor is still getting all available voltage, just on and off (off more) really really fast. So, at slow speeds, the motor will produce more torque with an ESC than with a resistor type speed control.