Long time APM user, but am setting up a large hex with 3DR Pixhawk for the first time.

The hex is trying to flip on takeoff as soon as I spool up.

The log file shows that there is a significant desired roll:

Things I have tried:
1. confirmed multiple times that the motors are in the right channels and spinning the right direction
2. Reloaded the firmware (AC 3.2), confirmed Hexacopter 'x'
3. Redid accelerometer calibration
4. Checked all radio calibration and radio reversing.

If I spool it up in my hands at a very low throttle, the motors respond in the correct fashion to stick inputs and if I twist the frame around.

I have attached a log file. Any help is greatly appreciated!

2015-01-03 13-59-37.log

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  • Here is a shot of the motor outputs. Def not right, especially considering this is sitting level on the ground.


    • Stu, i am using an orangeRx with sbus output to pixhawk.

      I had to change around the rcmap channels on the pixhawk to make them correct with my DX7s.

      Maybe it is some weird bug... but the heli responds to all stick inputs in the correct way. The only problem is that it is also trying to roll right the whole time.
      • ah ok, that's a pain..can't rewire. I guess the dx7 doesn't support reallocating? its a long shot either way.

        Which channel is roll? is it 2 as per my quick google? If so its not 1500 for centre stick, it stats at 1517, try retrimming it to 1500. might be enough to affect things at first throttle up. Actually more than one RCIN is above 1500. Although I don't understand why des roll is a high as it is from that.

        your AHRS_TRIM_X is -0.0105 ish Which I make to be about -0.6 degrees roll trim...bugger all though. might be worth retrimming though just in case.

        • Stu,

          You are correct. There is some bug with the RCMAP.

          I pulled out the 3DR PPM encoder, removed the SBUS, and set the RCMAP assignments back to default.  Now it works as it should!

          I need to escalate this bug to the devs... I would really like to use SBUS from the OrangeRX.

          Thanks for the help.

          • Hello Jonathan,

            I've had some strange behavior like described. It was in an iris x4 using an apm 2.6. The  fact is it outputed much more in channels 2 and 3 than in the others. After that i realised that parameter RC1_TRIM was set to 1100 us or so, wich is too low. After correct it manually to 1500 us throttle goes well.

            Must said: i had done channel arrangement in mission planner,not in transmitter, so:





            piloting mode:2

            Apparently, that parameter changes itself sometimes!so it's something you can try.

            • Pablo you are my hero thank you so much, I have been struggling with this problem for about 2 months. I did as you suggested and the problem is solved thanks again

          • Developer
            You probably find it easier to see what is happening with channels if you go to the fail safe page in mission planner or APM Planner 2.0

            The RC calibration page remaps the channels based on RCMAP params
          • Glad you sorted it, at least you can get flying, hopefully the fix will come soon. the simplicity of sbus wiring is very nice.

    • Oh, OK. I assumed that was you nudging the stick for roll. If you compare motor 2 of RCOUT with Channel 1 of RCIN they pretty much match so the Pixhawk seems to be wanting to do what it's being asked. So your RC Rx must be feeding something weird to the Pixhawk. You didn't mention how your RC RX was setup. The Desired Roll could be the result of this "something" providing roll pulses.

      • "If you compare motor 2 of RCOUT with Channel 1 of RCIN they pretty much match so the Pixhawk seems to be wanting to do what it's being asked."

        No, RCIN 1 is throttle for me. That is me raising the throttle to take off. When I do, all motors ramp up, but the left motors WAY more and it tries to flip.

        If you look at the picture in my first post you will see the Pixhawk is giving a desired roll. That is not a result of the RC inputs, which are all at neutral.

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