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So I was reading a few questions on drone, and I reach this one.

It said that an ESC is used between the PWM Arduinno's port and the motor. I don't really understand what it means. According to what I understand, a PWM is a varying signal and you just need an electric relay to receive this signal so that the motor receives correct voltage.

However, in other article I read that there are many different ESCs, with firmware and many other parameters to be taken into account. It seems quite overkill for what a relay does, so I am wondering:

  • What is inside an ESC?
  • More important, what does it do with PWM signal that could not be achieved with a relay and is essential to command the motor?
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An ESC is an Electronic Speed Controller. It's purpose is to control the speed and direction of a Brushless DC Motor.

A Bushless DC Motor ("BLDM") is not like other motors. You can't just provide it power and it will spin. Instead it is made up of three (or multiples of three) electromagnets along with a permanent magnet on the rotor. Energising these electromagnets in the right order at the right time (and the right amount, too) pulls the permanent magnet around in a circle, making the motor spin.

It's the ESC that has the job of controlling these electromagnets.

You provide a PWM signal as a digital speed indication. The ESC then interprets that as an indication of how fast you want the motor to turn, and excites the electromagnets in the right way to make that happen.

Oh, and no, you certainly never want to provide a PWM signal to a relay. A PWM signal switches hundreds, if not thousands, of times per second. A relay is capable of switching, at best, maybe 10 or 20 times per second. Relays don't drive motors. Motor drivers (or at the bare minimum, MOSFETs) drive motors.

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  • You could get a brushed motor instead of the BLDM, so you don't need an ESC. But you'd still need something like a motor driver or MOSFET, since the Arduinos digital pins can supply enough current for a motor. – Gerben Jan 3 at 15:45
  • Thank you, exactly the answer I am looking for. I just wait for some people to see the question before accepting it. I have a question as a result of your explanation: is an ESC specific to a motor (I suppose the architecture of the electromagnets could influence the timeline of energise)? And could you explain please the word "MOFSET"? – totalMongot Jan 3 at 19:39
  • @totalMongot Metal Oxide Semiconductor Field Effect Transistor. Like an electronic switch. Yes, different motors have different characteristics, but in general they are only minor differences and the only key things you need to consider are the current (select an ESC that is powerful enough) and the maximum acceleration rate (which you control with how fast you change your PWM values). – Majenko Jan 3 at 20:10

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