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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  • I recently built a Sky Hero Spy 750 w/KDE 2814XF-515 motors and Maytech OPTO ST ESC's.

    It has Pixhawk (genuine) FC.

    rx: Frsky x6r using Sbus

    I could not get 6 motors to spin with those Maytechs; a total of 8 ESC's. I thought it must be the ESC's, so returned them in exchange for ZTW Spiders which haven't arrived yet.  Independently using the receiver to calibrate ESC's, the motors sounded great, until everything was hooked up to Pixhawk. It did just what was in the video above. I spent hours reading, trying different things, thought for sure I must be overlooking something.

    So just for fun I took one ESC off my Y6B to replace one Maytech and all six motors worked! I then replaced all the Maytechs with the 3DR ESC's and I was able to fly. A bit sluggish, with a some sync problems at lower throttle, but the copter flies. The ESC positive wires are not connected to Pixhawk. 

    On the wiring side, I use a HobbyWing UBEC for the rail, and 3DR PM going to the power connecter on PIxhawk.

    I also ordered some HobbyWing XRotor (non SimonK) to see what they do.

    After reading this thread I'm not having warm fuzzy feelings that putting on different ESC's is going to fix the problem, although Kloner said the Maytech worked for him and the ZTW Spiders did not:


    I certainly hope there is a solution and it is something I'm doing wrong, but I'm not seeing anything could be incorrectly wired.

    There is also this thread that discusses issues with Pixhawk and power connections:


    I'll be watching this thread closely as although the 3DR ESC's are "working", there still are sync problems particularly at low throttle and I suspect the timing is too low for these lower KV motors. So KDE has their own at $58.95 apiece; something I wanted to avoid, but at this point if they make the motors perform, I'm nearing the point of desperation.

    • I should note Kloner referenced in the above post was using Naza, not Pixhawk.

  • Artem,

    It is simple to check if 3v3 pwm causes the issue, just use any spektrum receiver, they are all 3.3v pwm output!  As proven here


    • Again, as mentioned, i think it is both 3.3v pwm and QC of some of ESCs! Reading back few posts I mentioned that I had 2 afro 30a on the same SK verison one would loose sync one would work fine. And as seen in the xoltry's video he doesn't use a 3.3v RX, I want to see another video of those ESCs/motors with a 3.3v RX I think it could be even possible to supply only 3.3v to a frsky RX and perform the test again. 

  • I just moved from APM to Pixhawk and having massive sync issues. I'm using Afro 30a escs with SS v3508 700kv motors. They flew perfect on APM but as soon as I wired up the pixhawk I was having tons of sync problems, I can't even power it up fully. Below is a video of my issues. I've read through this thread and seen people post about having a ground wire for the signal connected (right now I only have signal) i've also seen mention of flashing new firmware on the escs. Can anyone confirm that either or both of these solutions will solve my problems? If not I'd much rather just purchase new escs that work well with pixhawk. I need 30a though and the only escs i've seen posted that work without issue are the 20a 3dr. If the two solutions above won't work with 100% reliability (as far as 100% is achievable) then can someone recommend a different brand 30a esc that will work perfectly with pixhawk?


    • Yes connecting each ground of each ESC to Pixhawk will solve your problems !

      • Rewired my quad with grounds for all the ESCs. It might have helped the problem but it is still completely unflyable. It just takes a little more power than before to bring up the sync issue now. I have a usb linker on the way and will try flashing the latest simonk firmware. Hopefully that will cure this problem. 

        • Sync loss is not pixhawk problem, but esc/motor issue. out of my experienceif an ESC / motor combo passes at bench test  for sync loss pixhaw will never be an issue as long as all grounds are connected. Update your ESCs f/w this should solve the problem.

          • Sorry, I've been through all of this and still I have to back up FlyHigh, there is something odd with the Pixhawk (even despite what 3DR is saying).  

            If you watch this video, you can see that even with the ground wire connected it still has the problem.  The biggest point though is that if you remove the power module (at least in my situation) it seemed to resolve the issue entirely.


            Furthermore, this other video shows that my motor and speed controller itself passes bench test, unless connected to the Pixhawk.


            And another video that shows the same situation, where a speed controller works fine when not connected to the Pixhawk, then exhibits the problem when connected to the Pixhawk.  This is a non-simonk speed controller.


            Even though my quad is working properly now with 3DR branded speed controllers, this issue still frustrates me when someone waives their hands and pretends the problem doesn't exist.

            • Been using pixhawk/clones since August on various setups ranging from 3s to 6s, 8"props to 17" props, 340kv, 380kv,  400kv, 700kv, 750kv, 980kv without problems. ESCs afro 30a, afro 20a slim, ZTW spiders 20A, 40A, HW xRotor 40a.  Always bench tested my ESCs with your method before putting them on a model with GND connected to pixhawk. as far as I was able to research the problem is with certain ESCs not handling 3.3v PWM correctly. I've seen cases where two 30a afros with the same SK one was causing issue the other was not. On opening them up I could clearly see differences in PCB quality, soldering and even one had afro mark on silkscreen the other one didn't. both ESCs were purchased from HK within one month of each other in April, never had issues with 20a slims though. 

              p.s. in my opinion it is more like some motors are designed to run on 91 grade gas, others on 87 grade. same with pixhawk, it is designed to run well with quality ESCs. most of the high grade MCUs these days run on 3.3v, days of arduino are almost gone, unfortunately some ESCs cannot handle 3.3v PWM correctly due to design others due to QC issues. guess what happens if you put 87 grade gas into Audi Q7 repeatedly?  

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