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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    • Finally, here the test Pixhawk / esc's Afro30a simply with ground connected.
      The sync problems are solved.
      Firmware 3.1.4 rc1 - RC_SPEED: 490 (default)


      Ciao - Giuseppe

  • Anyway its nice to have  explanation from officials not guessing on forums,thank you...I think you should highlight this somehow with bold leters all around wiki....

  • Developer

    This is the scope shot Craig attached but Ning is somehow not showing:


    This is how the signal looks like with ground not connected. You really don't want to have those spikes on there. I hope this illustrates the high-frequency complexity that is associated with this issue. Just having "somehow" common ground is not enough when talking about noise immunity.

  • Emin, probably a month ago had not yet known the problem of sync issue and the term of comparison was the ultra-proven APM.

    but certainly if connects the ground is the solution to permanently solve the problem and fly safely, I quickly run to disassemble my okto / esa etc.. and make the suggested change. ;-)

    Ciao - Giuseppe

    • I guess there is no other way...JUST DO IT all over again as many times before...

  • Developer


    Lorenz and Jeff and I finally had some time to work through this and I need to post Lorenz's comment from the drone-discuss list.

    Hi all,

    I have seen quite some cargo cult (http://en.wikipedia.org/wiki/Cargo_cult_science) when it comes to interfacing PWM based motor controllers.

    I feel I can contribute by helping people to focus on the right aspects during troubleshooting. After having tried all ESCs reported as "not working" myself successfully, I did a little write up to be referenced in the future. It tries to be a helpful troubleshooting resource but also serve as reference. Note that you can register yourself on the page and edit it if you feel parts of it need updating.


    The executive summary of this is:

    1) Pixhawk works with every ESC out there that works with a normal RC receiver. Really. Because it sends the same type of signal.

    2) The flight stack has to ensure that initialisation requirements for the ESC are met. The two most popular: 1) requiring a low pulse, e.g. 900 us or 2) timing out after a few seconds without signal. The native stack eliminates both by sending a 900 us pulse at boot and raises this to about 1100/1200 when armed. It does this only for multicopters.

    3) People need to get their wiring right. Always connect signal and ground. Check your ESC type to decide how to connect the +5V line. Pixhawk will never mind how you connect it, but your ESCs might kill each other if wired incorrectly.

    Basically you can get away with using the power ground as the signal return with the APM but you cannot do that with the Pixhawk.  You must connect both the signal and the signal ground in order to make the ESC work, otherwise the PWM signal looks like this.

    Displaying PWM_LineGlitch.png

    Video Here. http://youtu.be/6C1YG1e2aTo

    • I find the accusations of "cargo cult science" funny in this situation as it is exactly what Lorenz has done.  I have demonstrated a repeatable issue, with isolated variables, and he has waived his hands and claimed that Pixhawk 'works with every ESC out there'.  Based on some of Lorenz's posts he feels strongly about the quality of the Pixhawk (which I am by no means questioning here).  However, I think in this case his feelings about the Pixhawk have caused him to fail to heed his own advice, which is " to avoid becoming cargo cult scientists, researchers must avoid fooling themselves, be willing to question and doubt their own theories and their own results, and investigate possible flaws in a theory or an experiment." Anyway, I don't feel that the dismissive attitude that calling this 'cargo cult science' implies is conducive to finding a solution to this problem, and I'm sorry I wasted so much text trying to explain how I feel about that issue.  To give some perspective, I have purchased 3DR branded ESC's now and I believe they have solved MY issue, however in the interest of contributing to the community I am still here trying to help so that others can benefit.  I would be disappointed if the conclusion was reached that there is no compatibility problem, because that is not true.

      Moving on, I read the thread at drones-discuss and while it's great that everyone has come to a consensus that having the signal ground wire connected is the recommended setup, I have had the signal ground connected since I came to the same conclusion over two months ago on Feb 21, as per this youtube video.  Now the key word is that it is better, since it still has problems I described and demonstrated in the original post in this thread.

      Giuseppe D'Angelo's videos above demonstrate the exact issue I have with the Afro's, and although he doesn't have the ground connected in those videos I would not be surprised if he has the same problems after, as I still do.  I'm interested to see his results in the coming days.

      This video: http://youtu.be/6C1YG1e2aTo basically reiterates what I concluded over two months ago, but based on the sound of the motor in that video Jeffrey is moving the throttle stick up and down instead of using a throttle hold switch and instantly turning the throttle from 0-100%, so it is really not the same test.  It would be interesting to see it conducted properly to see if the sync issue still exists with the ground connected with that motor and prop combo.

      So, what's next?  Craig I understand you are still waiting on that T-Motor you ordered to try and replicate my problem.  Will you still be doing those tests, or is this the end of the road for this problem as far as you're concerned?  Because if it is that would be a shame.

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