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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      • The ATC parameters should have nothing to do with the altitude hold issue.

        The ATC parameters are used to "soften" the response of the system *only* to pilot inputs.  The issue is that after a successful Rate PID tuning, using either Autotune or manual methods, the quadcopter can be too sensitive to stick inputs on Pitch Roll and Yaw.  It is very "sharp" and reacts very strongly.

        In the past, people used to turn down the Rate PIDS to make it softer, but this also makes it less stable relative to wind gusts, etc.  ATC allows you to make the quad soft to your inputs, while also being stable relative external forces.

        • So ,what's the different between ATC parameters  and  RC_FEEL_RP??


      • I see them quite differently. The PID,s setup is about how the flight controller responds to its sensors and puts the appropriate feedback to achieve stable flight, the size of the machine also plays a roll because a large machine needs more input compared to a small machine. The ATC values appears to control how quickly a flight change from the guy holding the RC transmitter is acted upon. With the values in the 3.2.1 download made my machine feel light an aircraft carrier, response was very slow but only in stabilize or throttle hold. In Loiter it was fine, not sure why this happened but probably because my inputs in Loiter where processed thru the Auto Pilot and the ATC values were not needed.

        Keep up the good work, I have learnt a lot in the last couple of months myself.


        • My craft has a very crisp response to input when in Stabilise mode, so it will be interesting to see how the ATC params affect it.

          When you changed your Throttle acceleration P/I, did you increase or decrease the values? Mine are currently at 0.5 and 1.0 respectively. I understand that you need to maintain a 1:2 ratio between P and I in this case.

          Incidentally, I have posted some graphs of my altitude data in this thread:


          • Im flying a 800mm size Hexacopter. The ArduPilot site recommends starting at P=.75 and I=1.5

            see these links it may help.



            These are very helpfull

            • I've changed even Kallman values... It's not jumping now, very rare a little height jumps, BUT its slowly descending on 50% throttle, when I'm flying left/rigt/forward/backward it sometimes holds altitude but rather fullthrottle into the Sun! Reasumming, althold/poshold not working... It's even worse for me on 3.1.5. And vibrations are not higher than +3 and -3, Zacc is very stable... Just plot of throut is very jagged in comparision to linear thrin. I don't know how to do now, almost 1 week of tuning, I've touched almost every value of baro, throttle, althold, filters... 

              • Slow descent to 50% throttle looks like too much I parameter in PID regulator.

                I your case, I'd recommend to start over full setup. It is VERY important not to skip any step, including full new radio calibration.

                Best would be:

                1. Save all old values to file.

                2. Reset all values.

                3. Start wizard with flashing 3.1.5 firmware. 

                It is very important to make everything at right time in right sequence, it assures you that you did not miss anything important.

                • Thanks Marko! 

                  Now it looks like all uncontrollable jumps are gone! I've set everything from scratch, first flashed my pix with arduplane then again with arducopter 3.2.1. Set rc values to 1100-1900, calibrated, autotuned, inverted pitch ofcourse etc. Now it holds altitude in althold, loiter, poshold, BUT, when I move my quad left/right/forward/backwards it ascends! Getting altitude when race'ing my quad! When I release sticks, it slooowly descend to starting altitude and trying to hold at one place, sometimes it jumps 0,5-3meters but never like before. It also take's a while to grab altitude by quad in althold modes, it really needs stable altitude in stabilize to switch to althold/poshold/loiter. On mission my quad ascended 10-20 meters when move'ing to next waypoint, then descend to preset wp altitude and again between every wpts. It seems like some PID's are too high... I lowered PID's, its now sluggish but when I'm moving it gives high frequency wobble sound... I think thats the reason of quick altitude gains...

                  Should I enable feed forward? Ofcourse ATC values are preset to 0 rather than 108000 or something... Need to change it too, maybe wobbles will be gone... 

                  • What can be Dangerous for me and for my quad on big grass field? I can only crash my quadro :) It doesn't go under desired altitude! It only jumps upwards! I did it all, still the same, when raceing it gets very fast more than 100m altitude, I lowered pids but still gets oscillations in althold/phold. Stabilize is very good and stable even with strong winds. I think that I need more tuning on pids... And on auto mission it just stops above waypoint till get WP altitude... NEVER goes UNDER starting altitude when I trigerred althold/phold/loiter.

                  • I'd recommend the following actions:

                    1. Set P, I parameters 10% lower that autotune.

                    2. Make test flight in stabilize and record IMU.

                    3. See log for vibrations and check vibs are in preferred diapason.

                    4. If not, get rid of vibrations.

                    5. Rerun autotune.

                    6. Make tests once again.

                    You really ARE brave man to let drone on AUTO mission without stable alt hold.

This reply was deleted.


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