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sorry if this has been answered before or if this is something really naive/impossible. my experience is mainly with SW dev and I am trying to do this for an RC car so here it goes:

Turns out I have a servo that is connected to a receiver, this servo unfortunately goes by default beyond the min / max angle that I need (hence it starts to make a buzz).

I want to ask if its possible (and how) to given the same pwm signal from the receiver and an intermediate circuit with 2 potentiomenters (one for the min and one for the max angle) limit the angle the servo moves.

So lets say if I get the PWM signal that moves between 60 - 120 deg, with the intermediate circuit that I am trying to do I want to limit this on the min to be 70 and on the max to be 110.

so the signal and voltage will still come from the RC receiver and will be connected to said circuit and then the output of the circuit will go to the servo with the set limited angles by the potentiometers.

I have been reading over the internet and learning about servos and how they work; I know that you can control a servo with a potentiometer with the 555 circuit and even with an arduino and whatnot but what I need is to limit the pwm signal that already comes from the receiver in the minimum space possible. Any thoughts?

Again, sorry if this is a naive question, this is not my area of expertise.

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  • \$\begingroup\$ The pwm is used to drive your motor, actuator, or what have you. To be a servo, there must be a feedback loop, where something in or attached to your motor, actuator or what have you, sends a signal back indicating it's actual position. What is that signal in your case? Do you have access to it? Do you have a schematic circuit diagram of what exists now? \$\endgroup\$
    – Math Keeps Me Busy
    Commented Dec 4, 2020 at 3:56
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    \$\begingroup\$ This is a job for a small microcontroller. Measure the duty-cycle of the incoming PWM, limit it to whatever you need, then regenerate it. \$\endgroup\$
    – brhans
    Commented Dec 4, 2020 at 4:52
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    \$\begingroup\$ This is a severely impractical complexity/calibration nightmare to do in analog circuitry, and I speak from having tried essentially that as an analog high-rate ESC in my youth. Use an MCU! A modern computerized transmitter would also allow you to fix this at that end; there are some open source firmwares for reflashing... \$\endgroup\$
    – Chris Stratton
    Commented Dec 4, 2020 at 5:03
  • \$\begingroup\$ What is generating the transmitted signal? \$\endgroup\$
    – Bruce Abbott
    Commented Dec 4, 2020 at 8:21
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    \$\begingroup\$ A micro controller will be by far the physically smallest solution to this problem. And yes, people do put things like SOIC ATtiny's and PICs in heatshrink in wiring harnesses - eg, someone sent me one to convert brushed motor PWM back to a servo signal to feed a brushless ESC in a tiny helicopter (though reflashing the ESC itself would have been better). And you can rig up some training scheme so you don't need the potentiometers. But also consider the traditional solution to this problem, which is to to connect the linkage further in on the servo horn. \$\endgroup\$
    – Chris Stratton
    Commented Dec 4, 2020 at 18:34

1 Answer 1

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As suggested in several comments, it seems the best way would be to use a microcontroller that would be sufficiently small to make it fit inside a heatshrink tube and be in between the receiver and the servo!.

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