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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    • Well, possibly success but I will need to test further and see if I can make the fault reappear.

      I changed the Power/Ground connection from the power bistro board to a motor output port (Motor7/RC7) that has no signal wire connected.  (Y6 using Motors 1 thru 6) and the intermittent loss of sync on Motor6 seems to have gone.  At the very least it has reduced the frequency.  It used to happen on every bench test within a minute of spinning up the motors.

      Logs look the same as always with clean and consistent outputs to all motors, all relative to throttle and attitude as expected. I will recharge batteries and run them through again on the bench.  I used to get Motor6 to lose sync every time I spun up the motors, this is the first time I have been able to get through an entire battery without an issue on 3.2 on my Y6B.

      What concerns me is that I have been running 3.2/Pixhawk on my 250 quad for a while without any issues and that I know that other people do not have this issue with exactly the same gear.

      I thought it was a motor or ESC issue but I have replaced and swapped position of motors and ESC's and the problem remained the same.  I ruled out faulty Pixhawk as I could eliminate the issue all together buy reverting to 3.1.x firmware.  This is still the case.

  • Please note this comment at RCGroups:


    Santiago (3drobotics)
    Dec 03 02:16 PM

    Hey Jonathan,

    Thank you for contacting Technical Support.
    Afro esc's do have sync issues because of the rated 1kHz input. The pixhawk outputs at 400Hz and is what to look for when searching for esc's. Officially I can only recommend our 20 amp simon-k esc's. I highly doubt you need higher but tell me a little more about your build and let me check if there is anything that might help with the sync issues.

    Best Regards,
    [Technical Support Engineer]

    Ok, so what does that mean? Is there are parameter setting in MP that could be changed? The ZTW Spider is rated at 600hz. Should I expect problems?

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    • Developer

      I spoke to Santiago today and cleared up his misunderstanding on the ESC update frequency.

      • I assume that means the update frequency is a non-issue. Another item checked off.  Before trying out these ZTW Spiders, I'm taking notes.....lots of them.

    • These PWM ratings are very confusing and/or misleading.  It is physically impossible to drive a 2000uS PWM signal at more than 490hz.  As in: basic laws of the universe impossible.  

      So any ESC that claims to take higher inputs is suspect.  It is possible they can go faster, with a shrunk PWM window of less than 2000uS.  But this is not clear at all.  

      IMO, ESC's that market high refresh rates are suspect of selling snake oil.  

  • FWIW, I've got several Hobbywing Quattros in use with Pixhawk, never a problem with those.  I also have some of the new Hobbywing Xrotors coming so I'll give those a test.  

    The problem with this issue is that a lot of the people claiming to be "experts" on the forums, and talking about what works, what doesn't work, really have no idea what they are doing.  Monkeying around with test setups, flashing different ESC firmwares, etc, without understanding what is actually different in the firmwares, nor hooking up an Oscope, etc.  They're really just playing the lottery. It's not science.

    Craig has been asking people to send him a "defective" system for a year, and nobody does.  Actually, I think one person did a while ago, and the wiring was a dog's breakfast.  It worked fine after some tinkering, IIRC.

    • The setup that was sent to Craig was mine, I don't know how you would describe the wiring on it a 'dogs breakfast'.  It is just one motor, one speed controller, and the power module.  When I sent my setup to Craig, he was exceedingly nice and responsive.  But he said they couldn't recreate my problem.

      To check to make sure I'm not insane, I re-ran the test and, surprise, I can recreate the problem.  Here's the new video.

      You are right on some points though, I really don't have any idea what I'm doing.  I _am_ monkeying around with test setups and flashing different firmwares.  I don't know what's actually different in the firmwares, and sorry, I don't have an oscilloscope.  I guess I'm just playing the lottery.  I wish there was someone, when presented with a reproducible problem, had the skills, experience and tools to find out what the issue was.  

      • I'm either misremembering, or there was somebody else who sent it to Craig that you are not aware of.

      • Developer

        That is really curious.  I don't see any difference between the way you had it set up and the way I had it set up here.  I should have taken a video...Anyway, now I am curious about the interaction with the power module.  When you took the power module out of the circuit, what were you powering the Pixhawk with?

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