Hi All!

My Pixhawk is installed on Mariner quad (500). With the version 3.2 it has many nice flights, with very good ALT Hold control and AUTO flights.


After recent upgrade to 3.3.2, it changed its behavior: in Stabilize all is OK, stable and smooth control, hovers on 50% Throttle. When switch to Alt Hold, it starts rising up at full throttle! When switch back to Stabilize, all is OK with the control. Sometimes the rise up is hard to compensate with the trottle....
Looking at the logs, all seems OK, except the inconsistency in the IMU - accelerometers 1 and 2 shows different phase after switching to Alt Hold.

Do you have any explanation? Hardware fault or 3.3.2 software bug?

The last test flight log is enclosed.

Test_Alt_Hold2712.bin

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Replies

  • I had baro issues on both copters, the Mariner is closed and watertight....

    There is bed for foam on the lower half of the Pix box. The original foam is very light and cannot damp the wind and propeller bursts.

    3702168226?profile=originalHere is the barometer, that should be protected from the foam :

    3702168165?profile=originalYou have to find porous, but very dense polyurethane, and cut higher block, that should be very tight to the barometer face when screw the box back. I use piece from sports mat.

    You shouldn't glue - need a free access to the air, but thru the polyurethane structures.

    • Thanks for the detailed guide!
      I've opened up my Pixhawk's case, and had the same black sponge in it. I've changed it with a piece PU foam stolen from my daughter's playing mat ;)

      Anyway, how about the reading of the baro sensor? Mine has actually showing a 1013 press_abs, and local airports QNH now is 1027 mb.(it's just 5km from me) Shouldn't be the same value for Pixhawk's pressure reading and actual local QNH??

      • The absolute value is not important, and even can rise slightly. The baro is not thermostabilised, and the readings depend of the temperature.

        Most important is to give correctly the relative height between the launch position and the current height.

        In the mission planner you can put the actual height of the launch point.

        • Hi,

          I had just today chance to try the Pixhawk with the changed sponge to a more thicker piece of mat.
          2 flight went good. 
          But the 3rd one, the 2nd part of it, looked like when a machine lives it's own life.
          Speeded up itself, went into a massive dive, and crashed from appr. 30meters, in a 30-40 degrees angle flight path.

          There was no reaction to RC controls, was no chance to recover from this unwanted flying situtation.

          RTL didn't help. If you have time, would you pls check the log file? I'm just curios what do you suspect that caused the crash.
          As I heard from the 50m distance, it had full throttle up. But log shows voltage drop and double AMP when this event happened.


          20.BIN

          https://storage.ning.com/topology/rest/1.0/file/get/3702807157?profile=original
          • Hi,

            First i can see, that you fly at high speed - 10-12 m/s, that is not good for non tuned machine.

            When you switched to RTH at the end, the satellites drop to 7.

            The copter went in roll oscillation, that shows not good tune. Should tune the PIDs.

            There is a lot of magnetic field change - seems there are magnetic parts (screws), that interfere with the compass. Have to replace all around with plastic screws.

            Do you use the compass on the GPS post?  In the log only one is shown.

            The copter is overpowered - ThrOut – 300 average - have to tune that, and use damped controls for throttle, pitch and roll - machine seems too "nervous"

            You should set proper Failsafes - Battery about 13 volts (all the times generates FS)

            And the fence should be real one in circle and height, to avoid FS

            The radio control was OK, all commands were received, but the copter cant respond properly.

            • Did you switched 3 times the RTL or the copter breach itself the fence?

              Sometimes the bad reaction to the radio commands are result of receiver bad wiring.

              I always use second 5V BEC to the receiver and the Pixhawk servo rail. And use additional ground wires between receiver and Pixhawk.

              The FPV should independent BEC from the battery. No any connections to Pixhawk.

              • Hi,

                Thank you Vesselin to looking into the log.
                Copter is tuned, but not with the autotune function. It flew stable till the crash.
                Don't know why the SAT number dropped to 7. Maybe it's due to the quality of the GPS. It's a Chinese copy, mass production with a M8N module. But it could be also a fake M8N GPS module... 
                SAT's are maybe lost also due to the small surface of the GPS antenna, and when the copter was in pitch down position, the small and ineffective antenna lost a lot of SAT's.
                This is just my theory...

                Magnetic field: good question. It might be an issue. The GPS antenna puck has 4 screws. It's metal screw, but didn't check is it magnetic or not. Since the crash I've a new GPS, which comes from EU. More reliable.
                And yes, only one compass was used, the internal. Because it was unable to calibrate the external compass which is in the GPS.


                What value should the ThrOut should be? One way to make it less power to change to smaller props?

                Battery which I suspectedd to, the weak point of the system. Need to change to high quality 6S LiPo.

                RTL was activated once, when I saw that something uncontrolled happened, but didn't help.
                The Pixhawk itself powered from 2 sources, as you described. One from the power module, and one from the servo rail via 5V BEC.

                My conclusion of the crash is that: stay away from cheap Chinese clones. I already thrown away the clone GPS to the waste bin, and the clone Pixhawk will follow soon.
                Existing battery will be downgraded to a test battery which will never fly again, and buying a German well trusted LiPo.
                Then re calibrate the whole copter, and make a full auto tune sequence.


                • There is issue with the compass, you should never use the internal for main compass.

                  It is good to have it working, but not as main.

                  The compass that is in the NEO8M should be perfect, as away from the copter body. Look at all screws in the NEO body - maybe are magnetic? Remove them and test. Then you can just glue the plastic parts. If still compass bad - it is damaged.

                  But there are some more issues...

                  Look at the picture:3702930137?profile=originalThe ATT Roll doing huge Roll variations (ATT DesRoll is good), that means that copter cannot balance itself, due to kind of mechanical failure - huge motor/arm vibrations, not good ESC/motor/cables, or problem in propeller.

                  Liik at the left/right arms, there should a problem.

                  In general the machine is over powered, the ThrOut should be close to 500.

                  Probably the platform need the weight of the gimbal/camera added to have proper weight. You can use larger battery if no plan to use camera.

                  If you plan to add camera, use dummy weight around 400-600 gramm (or more) depend to the camera/gimbal weight you plan to use.

                  Then test and see what is the ThrOut. Could be in range of 400-600.

                  Battery is not so bad - it still gave 13V at full throttle at the end!

                  3702930247?profile=original

                  • cool detailed .bin log file analysis :)

  • Hi Vesselin,

    Is your issue solved by disabling IMU1 or IMU2, or just with moving the buzzer away from the Pixhawk?

    I'm just asking because I've the same issue as yours.

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