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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        • Just the BEC on the Afro ESC.
          • Developer

            Can you please check the cable between the power module and the Pixhawk to make sure that all of the wires have continuity and that ground is continuous through that cable.

            Then remove the connection from the servo rail to the ESC and verify that there is continuity from the ground pins on the servo rail back to the ground connection to the battery.


      • It's really strange that it happens immediately for you but not for 3DR when they tested.

        Out of interest, did you ship the LIPO with the Pixhawk/motor/ESC?  I'm wondering if there's some strange voltage sag that happens when you flatten the throttle.

        • No, I didn't, but it happens both with my 2200kv motor on a 3S 2200mah lipo, as well as on my 1100kv motor on a 4S 3700mah lipo, so I doubt it is related to the battery.

      • Read this thread although you aren't using OPTO ESC; it still appears to apply:


        For the 3D Robotics Pixhawk equipment, there is a hardware incompatibility of the Pixhawk to true, high-quality OPTO-isolated ESC circuitry. For OPTO-isolated ESC circuitry, the positive/negative control loop of the system must occur at each ESC port of the flight-controller, so that the circuitry is properly powered and kept separate from the full system. The Pixhawk hardware does not provide this, and rather, completes this loop through the ESC itself, grounding all ESCs to the central ground of the Power-Module. While this will work, it can introduce significant noise to the full system, as all ESCs are tied together to a central ground. For ESCs that are NOT OPTO-isolated, this will work and the ESCs will arm, but RF and electrical noise will pass through the system and can lead to instability issues or video noise.

        To solve this, customers have provided great insight to the hardware and the current solution (special thanks to Rob, Freddie, and Quoc for their insight), which is to introduce a grounding-loop to the system. This allows the OPTO-isolated ESC circuitry to properly function, and the overall system will work excellent for flight. This is created by adding a negative and positive loop from the Power-Module to the Pixhawk, using one of the open ports of the "Main Out" section. In this regard, adding a jumper from the Power-Module direct to the "Main Out" section will provide the negative-ground loop - then all ESCs will properly arm. Please see the attached image to help explain the proper jumper arrangement.

        • Developer
          I have asked Patrick at KDE to remove that post as it is pure gibberish. Unfortunately he has not done that and the misinformation persists. Please see this note in wiki:7 A Special note about KDE (and other) Opto Isolated ESCs http://copter.ardupilot.com/wiki/common-pixhawk-wiring-and-quick-st...
          • Thank you. Does that also mean the UBEC can be connected to the 'Aux Out' pins rather than the 'Main Out'? That's what I understood to be the case months ago.

            I am not qualified to give a "scientific" explanation, only observations. In my case, I observed 8 Maytech OPTO ESC's refusing to spin up all 6 motors when connected to Pixhawk, but calibrated seemed fine individually. This is in no way confirming xoltri's, only that I spent hours in vain trying to figure out what was wrong.

            If the ZTW Spiders do the same thing, what am I to believe? The 3DR ESC's work, but are not 100% on these motors. Maybe the timing is too low, I don't know. They are installed because I'm able to fly. However, there are times when they don't sync properly distinctly at low throttle, possible at higher throttle but my hearing may not be picking it up.

            IIRC, I took the following diagram from an Arducopter instructional page. The only difference is I blanked out the ESC BEC portion. I see no reason why there would be power issues with this setup. Sometime this week I shall find out.


            • Developer

              >>>Does that also mean the UBEC can be connected to the 'Aux Out' pins rather than the 'Main Out'? That's what I understood to be the case months ago.

              You can connect the BEC anywhere along the servo rail.  All the pins on the +5 rail are connected to each other and all the pins on the ground rail are connected to each other.

              • Just to be extremely clear to users: Other than the RC Input pins.  On that one, the ground pin is not connected to the 5V rail directly.

      • Moderator

        You couldn't by any chance post a copy of the log files from these tests, PM / No-PM? I'd like to see what's going on with board voltages etc.


        Nathaniel ~KD2DEY

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