Is it amp or volt switching on ESC that changes speed


Quick question

I understand that kV means revolutions per volt, but I’m just curious on how the ESC changes motor speed. Does it reduce the voltage or does it reduce the amperage from the max that it can output?

Just asking because I have 30A ESC, 25A rated motor, and Arduino. On burst or max throttle, the servo.write function is at 180. So will 180 “release” 30A, the max output of the ESC?

Just need to know so that if I buy 60A ESC I know to put the servo.write value to half, as to not break the motor.

Lastly, if my ESC smells weird, is it fried? I know this is common sense (magic smoke release) but just wanted to know. I forgot to shrink wrap the motor leads and they contacted each other. Now there is no motor ovement nor beeping.

From quad to tri… I’m very disappointed :disappointed_relieved:


Put basically, the brushless ESC sends a power to the motor, but since it has three wires, it does this at specific timing to activate a specific group of electromagnets in the motor for it to spin. The faster it does this, the faster the motor spins.

The ESC is controlled by something else that sends it the desired throttle (usually via a pwm (pulse width modulation) signal). This signal is usually between 1000 and 2000. I am not sure what arsuino library you are using to control the esc so you will need to read the specifics on that.

Generally if you use a powerful ESC it will not cause the motor to burn, as the motor will usually take as much current as it needs. If the voltage is too high then you can burn the motor coils. Also if you use a propeller that is too big on your motor it will cause it to pull more current and either burn the motor or ESC.

In your case if it’s your ESC that smells funny, then it’s likely a MOSFET on your ESC is fried so you will need a new ESC.

Hope that helps you to understand the basics, if you want to learn more check on Wikipedia about brushless speed controllers for the technical details.


I think the OP was asking if it is a change in voltage going to the motor that changes prop speed or if it a change in current going to the motor.

To my understanding there is no variance in voltage or current that is being delivered to the motor from the ESC when you advance or retard the throttle.

What does vary is the number of energizing impulses-per-second that the ESC sends down each of the three wires which connect it to the motor - the wires attach to electromagnets on the stationary part of the motor. These wires are energized by circuitry in the ESC in a sequence which interacts with one of three ordinary magnets in the rotating part of the motor - literally moving that magnet a little bit. When that magnet moves a certain distance the power in that wire is shut off and the power in the next wire is turned on, the next magnet is energized, and the sequence begins all over again. The faster these on-off-on-off sequences take place, the faster the motor turns.


Just same basic electrics:
Current is drawn from the source. Not controlled. So if your motor wants 30A, it would want to draw that from the ESC and battery pack.So your ESC and pack must be able to deliver.
Voltage controls your speed, and it is done with impulses send to motor. This is called voltage chopping (Ratio between applied voltage pulse VS off voltage pulse) The wider the applied impulse, the higher the voltage and the faster your motor will spin.
But the more voltage you give (wider impulses) the more current the motor would want from the supply.

Very simple explanation (A bit more complicated than that), but simply put:
Current is what the motor asks from your supply. And Voltage controls the speed by pulsing voltage to motor.
Always go for Max current your motor ask and what your controls can deliver.