Pixhawk causing motor sync issues.

I believe I have a problem with my Pixhawk and was hoping for some help.  Also posted this on rcgroups.

The issue is that when my speed controllers are hooked up to the Pixhawk they exhibit a bad sync issue.  However when they are connected to my old APM (3.1) or just a receiver directly they do not exhibit these symptoms.  This has resulted in 4 crashes now until I just tonight narrowed down the issue to the Pixhawk.

Can anyone advise what is going on?  Here are the specs of my setup:

Afro 30A ESC's with SimonK firmware (have tried all versions, and made my own with various parameters)

Tiger MT2216-9 1100kv motors

4S 3700mah battery



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      • Here it is again with RC3 in shown.  RC3 in noise is throttle moving between 1113 to 1115.  This happens on 3.2, on 3.1.5 it is less much less pronounced.

        I seem to be able to reduce the chance of loosing sync on motor 6 if I arm and throttle up straight away and keep above 40% which would be normal for flight but it worries me that I can make the motor lose sync, it has caused a crash once and stying above 40% throttle does not always stop the problem.

    • Hi Philip,

      Just to be sure I went back to 3.1.5 and that fixed the problem and also returned the throttle response to be smooth instead of strange with 3.2.  After about a minute I lose low end resolution, meaning that if I close the throttle and simply raise it a small amount the motors jump up to about 30%.

      Every time I revert to 3.1.5 the problem goes away.

      I have tried two Pixhawk boards, several 3DR ESC/Motors and even connecting ESC directly to Rx.  Always exactly the same issue , always motor no.6 always completely fixed by reverting to 3.1.5.

      I use 3.2 on my quad and it is fine.  I do not know what the issue is other than I am getting to the point where I am starting to feel it is software related.

      I will reinstall 3.2 and send you a video of the problem and also the performance on 3.1.5 before I send you my Y6B.  Would you agree that if I can show that the problem only occurs on 3.2 that something in the firmware is causing a problem and sending my Y6 to you would not really help?  Possible not a bug but something that shows up more in 3.2 and causes a problem that 3.1.5 doesn't..

      I have replaced,, bypassed and checked every possible combination and I feel confident in saying it is extremely unlikely to be a hardware issue unless I have three ESC and four motors and two Pixhawk boards with the same exact problem.  I am not trying to have a go just stating that I have tried to find the problem by looking for a hardware solution and have got nowhere.

      Usually, when a problem is this hard to solve I find that I am looking in the wrong place.  If is was an ESC/Motor, Wiring (This is a 3DR RTF built in the factory) than surely I would have found the issue.  If there was no issue it would not have flipped and crashed while simply hovering.

      xoltri, if you are using the 3DR PDB then the ground on the ESC PDB connector is the same as the battery -ve, there is no difference between battery -ve and ESC -ve so I do not think that there is a "ground Loop" or difference in voltage levels here.  Might be something to do with noise but I cannot think why it is always Motor No.6 for me and is the same with or without the PDB.  Also, 3.1.5 fixes the issue consistently, as consistently as I am having the fault when I try 3.2 on the Y6B

      • Alex,

          Have you noticed a difference in throttle RC_OUT vs RC_IN? When arming, my props spin on the slow side, but just a small throttle movement (one graduation on the stick), the motors seem to spin much faster than they should.

        To be honest, I don't recall if it was this way on my stock Y6B.

        Is there an adjustment in the parameters that give a smoother throttle response? Or is it inherent with the tx?

        • DG, Short answer, YES.

          This happen to me only after a short time armed.  The first time I raise the throttle it is smooth, only happens on the Y6 not my quad's.

          As the first time I ramp up is smooth I am guessing that it is not the Tx.  I have tried changing limits and resolution, even tried some EXPO setting but it is always the same.

          I actually think this is normal and OK.  It seems to be the code trying to account for small level offsets, not getting anywhere as it is on the bench and adding more power to compensate.

          If you lift the machine f the bench and allow it to level itself this gets less pronounced.  Don't fight it if it is leaning over, it will correct itself.  Problem here is that you have to test with props on!!!!

    • Hi Philip,

      If I cant get it fixed then I will send it.   It is definitely repeatable, so much so I don't trust it enough to get in the air.

      I. will let you know how the test go.  I am thinking/hoping that it is the PDB but you never know.

    • I can send mine back to you if you wish.  As per my latest youtube video the problem still exists.

      • Developer
        please PM me your Skype
      • xoltri, can you repeat your test, but hook ESC to a receiver supplied with 3.3v without any pixhawk involvement, also, can you open up that afro ESC and take a picture? 

        • Artem, not sure what 3.3v would accomplish.  It already works fine if I 1. Disconnect the power module from the Pixhawk (or remove it entirely) or 2. Control the motor directly sans Pixhawk with the 5V BEC on the receiver. 

          But sure, I can take the shrink off of the Afro and take a photo of both sides of the board.

          • I am wondering if this is 3.3v pwm having issues with some afros... 

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