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I have an RC/drone ESC that takes a PWM input signal at 3.3 V/5 V for throttle control, but has no onboard buck/BEC. I have the illustration below for my current setup.

This motor works excellent with a VESC ESC/controller that has an onboard BEC/5 V but I want to try it without a software-enabled controller. Currently, with the setup below, the ESC triggers an intermittent beep sound every second, which according to the manufacturer is the troubleshooting sound for lack of receiver signal detection. Even following the instruction to set up the throttle, it does not detect. I have checked the voltage at the signal and the POT is properly outputting a range of 0-4.9 V.

Now, my hunch is the fact that the ESC requires a PWM input that is in the range of 50-500 Hz, where the DC buck I have is at 300 kHz for its PWM. Although the POT is working properly, I assume the frequency is far too high for it to detect. I do need to use this setup, as I am using a trigger/spring actuated potentiometer which is hard to come by on existing controllers. Ideally I want to be able to control the throttle with my spring POT and DC buck.

Questions:

  1. Do I need a special servo motor controller to behave as the PWM signal for the ESC?
  2. Can I use a DC buck that outputs the proper frequency?
  3. Is there a simple PWM generator I can use with my setup? Or a way to reduce the frequency?
  4. Is my assumption incorrect here and should the buck be able to output a proper signal?

Please let me know if I am missing something here. This is going to be for a production product so we need to use a specific setup, cost, sourcing, etc.

Wiring Setup

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  1. Do I need a special servo motor controller to behave as the PWM signal for the ESC?

Yes.

  1. Can I use a DC buck that outputs the proper frequency?

No. A buck converter outputs DC. However you may want this to supply a suitable DC voltage for your PWM signal generator.

  1. Is there a simple PWM generator I can use with my setup?

Yes. Look for a 'servo tester' or 'servo motor controller'. These typically use a small microcontroller or 555 timer IC to produce the required signal, which is a 1~2 ms pulse repeated approximately every 20 ms.

Servo control

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  • \$\begingroup\$ Thank you I figured as much that the signal was not the proper type. I do need a very simple controller where I can reuse my trigger potentiometer. Ideally something that controls the signal with my POT instead of a whole package. So I will look for something like that. Would you have any recommendations? I see in that wikipedia page there is something simple I can search for. Maybe something like this? adafruit.com/product/… \$\endgroup\$
    – vm1988
    Commented Nov 1, 2022 at 19:23
  • \$\begingroup\$ If you want to control it with a pot then a servo tester like this protosupplies.com/product/servo-tester or a circuit using a 555 timer like this 555-timer-circuits.com/servo-tester.html will do the job. \$\endgroup\$
    – Bruce Abbott
    Commented Nov 2, 2022 at 20:13
  • \$\begingroup\$ Thank you, very helpful. Learning a lot about servo PWM. I was able to generate a PWM signal with my RPi pico using circuitpython. It ran the motor, but then got crazy where in rapid succession would move clockwise then counter. I then used a servo tester and it works perfectly. So I think I should be able to produce the necessary signal with a pico which works well with a pot. So it will take the pot adc value and set the pwm duty cycle to that of the pot. Just need to configure the 20ms pulse. \$\endgroup\$
    – vm1988
    Commented Nov 3, 2022 at 4:20

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