AC3.2.1 APM 2.5 Throttle pulsates in Loiter


I have a problem after updating AC to 3.2.1 from 3.1.5.

When in Loiter, the the speed of the motors rev up and down/pulsate quite rapidly. This was working fine when I was using previous versions of arducopter.

I have downloaded the logs, and have looked into accX, accY and accZ. These seems to be inside the range specified in the wiki at arducopter. (Log_vibrations.bin)

Please have a look at the Log.bin, and note the difference between ThrIn and ThrOut when I'm in Loiter mode.


Anyone having any idea what the problem may be?



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          • Could you try out 3.2 firmware? I think it is closer to 3.1.5 than to 3.2.1.

            • FW3.2.1 I solved by lowering the value of the parameter PILOT_ACCEL_Z FROM 250 TO 50 NOW is VERY STABLE IN FLIGHT and should not be more 'up and down

      • I tried to put MPU6K_FILTER = 20 - 5-10 -42 Hz but the problem remains or changes little, continues to be unstable

      • It's easy to find out. I'll flash 3.2.1 rightaway.

  • Is this altitude abnormality can be seen in AC 3.2.0 also? Almost everyone is talking about this issue after upgrading to 3.2.1 from 3.1.5. Have anyone tried 3.2.0? I have observed that mounting APM inside a canopy makes difference (even if Baro is covered with foam). Pls look into this data. I haven't tried 3.2.1 yet.

    APM 2.6_BaroAlt.xlsx
    • To get rid of this misunderstanding.

      Situation A: We have small quad (5x3 props) that flies on 3.2.1 without canopy, but with baro covered with foam. It flies very well in my opinion, which could be because it doesn't have high amplitude vibrations, only lots of small ones.

      Situation B: We have medium quad (10x4.5 props) that was tested on 3.2.1 with canopy and without.

      Yes, because of bigger props that are closer to controller, and generate vibrations with lower frequency and higher amplitude (in common words, props spin with less RPM, but do much more powerful swing, which generates stronger vibrations but less often), covering controller with canopy gives positive results. 

      BUT at the same time, on 3.2.1 firmware with vibrations fitting into allowed +-3 corridor, it behaves very unstable.

      At the same time, on 3.1.5 firmware behavior is solid and stable. 

      Which means, that problem appeared somewhere in between.

      • Ok, so here's result of testing 3.2 on my "3.2.1 unstable" quad. 

        1. I flashed 3.2 (MP was babbling about "flashing last version, borda enda suporta, maaan", but flased 3.2 as required).

        2. Recalibrated compass (It is important thing that people tend to forget).

        3. Forgot to put my inertial weight on APM, so it was catching all the small vibrations. (Some were damped though).

        4. Did a small testing flight. Well, altHold was solid, and loiter mode was acceptable. IMO loiter could do position corrections in more fluid manner, but it was not twitchy and that's important.

        5. Crashed :) Well... In loiter I decided to test how does it behave in forward flight, and drone started to descend. The cause was that battery got dried out (I have "land" failsafe on battery and voltage). 

        6. Set INS_6k_bla-bla-bla to 20Hz and tried to fly again. Noticed no changes, but due to dry battery I had not much time for experiments. 

        Bottom line. 

        It would be good for someone to also test 3.2 version of firmware. It should be somebody who has issue with 3.2.1, but flies stable on 3.1.5.

        Thanks for watching :)

        • I will try 3.2 but I am using apm planner and it doesn't give me the option to use old firmware. Where can I get the hex file to do it manually?
        • my hexa upgrade to 3.2.1 from 3.1.1 ,seems no problem with althold for the moment.

          my vibrations is not so good ,aboutXY +-1.8;Z -9 ~-12。

          maybe  3.2.1 sensitive to a certain frequency only.


          if your quad would overshootafter a high speed flight in althold mode? (like below pic show)Do you have any ideal, how to fix it?


          • Your graph diverges with "no problem for the moment" ;)

            1. What is power setup? motor kV, props.

            2. Did you do autotune? It greatly helps to find starting point for further tuning.

            3. It is pretty strange to have ROLL overshot after high speed flight, it there something you didn't tell us? ;) :) 

            4. If you are confident about 1-3 are working as should be, try lowering P on roll axis.

This reply was deleted.


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