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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  • I put a genuine 3DR APM 2.5.2, that was collecting dust, into my Quanum Nova to replace the factory APM that was in it. (The factory stuff requires custom versions of copter) The Loiter/AltHold pulsating started as soon as I upgraded to 3.2.1. After reading this info I started thinking the filter frequency could be my problem. Changed it to 20 and voila - no pulsing and a much better atlhold all around. Thanks to everyone here for this info.

    Andy Piper said:

    So this is really strange. If you look at the setting:

        // @Param: MPU6K_FILTER
        // @DisplayName: MPU6000 filter frequency
        // @Description: Filter frequency to ask the MPU6000 to apply to samples. This can be set to a lower value to try to cope with very high vibration levels in aircraft. The default value on ArduPlane, APMrover2 and ArduCopter is 20Hz. This option takes effect on the next reboot or gyro initialisation
        // @Units: Hz
        // @Values: 0:Default,5:5Hz,10:10Hz,20:20Hz,42:42Hz,98:98Hz
        // @User: Advanced
        AP_GROUPINFO("MPU6K_FILTER", 4, AP_InertialSensor, _mpu6000_filter,  0),

    0 is supposed to mean default which I think is now 20Hz (was 42Hz). So if setting this to 20 gives different behaviour to 0 it has to be some kind of bug in the initialization of the sensor. Given that there was quite of lot of work in 3.2.1 specificly around sensor failure detection, it seems quite likely that something was introduced in 3.2.1 to cause this.

  • Hi,

    I am too is experiencing this problem. Has anyone solve this yet? I used to fly AC 3.2 on bigger quads and flies smooth in all modes. Then I recently purchase the fat phantom shell  425mm from infinity hobby and installed my other APM 2.6 (running AC 3.2 also)  on it. Then started to experience motor pulsing in ALT Hold and other GPS related modes. Please see attached log

    2016-03-12 10-07-16.bin

    2016-03-12 10-07-16.log

    • Mine was vibrations and some tunning. Solve it.

      • Thanks. I made sure my vibrations were on the limits. What did you tune, may I ask? Thanks

        • Elvin:after tunning you need to solve vibrations, don't think that only being under limits, you are ok with vibes, the pixhawk add more vibrations measure I hope for this problem Leonard can clarificate better; I finally changed my hole copter trying component by component that produce vibration including the APM for a Pixhawk but, in case, tired,  I mounted on a tower of isolation systems (not recommended but works for me) I have this and over there, the pads on the four corners that come with the controller, better idea is become with less isolation and add more if you need or change them and test until your copter performed well, I have the two extreme, my other copter, the controller is hard fixed, no isolation and performs nice, 

          • Thanks Leonard and Cala!

            Changed my damping pads to moon gel and got less vibration on the X & Y but not that good on the Z. Checked all wires and any possible components that can transfer vibration thru the APM. Still, the problem exists. Any Idea why the vibrations on the Z axis is not that good compared to the XYÉ



            Cala I guess you're right, I too have another APM 2.6 on a 800mm quad and spend less time setting it up and flies great in all modes and I've been flying it for over a year already. Just decided to build a 400 size now and facing this problem. 

            Do you guys think I should switch to pixhawk in my case? I guess my APM is not right for my new frame (which is a fat phantom shell 425mm from infinity hobby).

            • If you migrate to Pixhawk you can enjoy the better last firms, if you have little space take in consideration Pixracer, the new board for little setups; Z values is common that are higher than x and y ones; if you don't solved with moon gel try with leonards orange foam under the corners or with this

              A thing that you can do easy, is to put aprox 50 grs weight over your controller well fixed with double sided tape until you recive the other dampening systems. (remember the compass if you use metalic material.)

        • Try autotune first and them you can do fine tunning,

          • Done that. but will try it again and see if anything change.

            Tried to graph my BaroAlt, Dalt and Alt and found out it's not tracking all together.


            Here's my vibes


            • Developer

              This looks like the classic vibration issue. It looks like it is just ok in stabilize but as soon as you put a PID loop around the accel it blows up.

              You may get away with dropping your Thr_Accel_P and I by 50% but vibrations are the cause of the problem. You can add vibration isolation or fix it at the source.

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