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Where has the MOT_SV_SPEED option gone?

Posted by Paul Revitt on November 25, 2014 at 6:38am

Hi peeps, I need help please!

I've got a tricopter running APM2.7(HKpilot) and I've having issues with the yaw servo. It's not at all smooth in it's action. It's Savox SH-0257MG digital servo that can run up to 250Hz refresh rate, but from what I understand APM defaults to 50Hz.

From what I read there used to be an option in Advanced Config that allowed you to choose between 50, 150 and 250Hz, but in AC3.1.5 the option doesn't seem to be there.

Is there a way for me to choose 250Hz so my servo works smoothly or is the only option to install a analogue servo? Any help would be much appreciated.

Cheers for reading,

Paul

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Tags: mot_sv_speed, digital, hz, rate, refresh, servo, tricopter
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Replies

  • Paul Revitt November 26, 2014 at 3:31am

    I installed AC3.2 last night which is the same; no MOT_SV_SPEED setting. I've got an analogue servo on the way, but I'd like to get this digi one working well if I can.

    No body kow what happened to this option..?

    • Adrian Round > Paul Revitt November 27, 2014 at 7:15pm
      I think you will find that RC_SPEED is now used to set the servo frequency. The description talks about ESC update rates but discussions on the Trad_Heli forum suggest that it also applies to servos.

      Cheers,

      Adrian
      • Paul Revitt > Adrian Round November 28, 2014 at 1:36pm

        Hi Adrian, cheers for the reply.

        I gathered as much from what I've read but there's no definitive info out there. Or at least that I can find.

        So the default RC_SPEED setting is 490, which AFAIK means the ESC's are running at 400 as that is the max for the APM. But surely the servo can't be running at that as it would burn it up..? I know the max for my digi servo is 250Hz.

        I read something suggesting that output ch7 and ch8 default to 125Hz for the servo, but it could be 50Hz..? It also suggested, as you said, that any other setting than 490 RC_SPEED would change all 8 outputs, over-riding the default on 7&8.

        I don't know how the delve in to the code to confirm this, not do I have a 'scope the check it with.

        Is there anything definitive on this?

        Thanks again bud :)

        EDIT: I should say that I'm running a standard tri setup. Outputs 1, 2 & 4 going to ESC's and output 7 to the yaw servo.

        • Adrian Round > Paul Revitt November 28, 2014 at 6:03pm
          I had a look at the code and could no longer find any references to MOT_SV_SPEED. I will scope the output of ch7 on my tricopter (3.2) and see what is happening.

          Cheers,

          Adrian
          • Adrian Round > Adrian Round November 29, 2014 at 10:07am
            Okay, I put my logic analyser on the APM outputs. Running APMCOPTER 3.2 on an APM 2.5 board in tricopter configuration with RC_SPEED set to 490 results in:

            ESC on outputs 1,2,4 490hz
            Servo on output 7 50hz
            • Paul Revitt > Adrian Round November 30, 2014 at 5:39am

              That's great buddy, cheers for taking the time :)

              So it is actually outputting 490Hz to the ESC's. Hmm, maybe it's just the Pix the limits to 400Hz. Well that's good.

              I've since fitted a analogue servo to the yaw and it's much smoother, which makes sense with it being at 50Hz. Looks like digi's are a no-no.

              Thanks again.

              Paul

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