Switching to alt Hold or loiter cut off my motors.



i running apm2.6 with latest "stable" 3.0.1 firmware. I use latest  MP 1.2.83 to make my settings. In moment my copter fly very stable in stabilised mode. Today i decide to test other flight modes. At first i tried AltHold. Switching into this mode nearly cut off my motors. See graph on top. Of course i have corrected the THR_MID parameter as shown on the ardurcopter homepage. My value here currently is at 428 for 6kg take-off weight.

Some words about the copter. It is a hexa for heavy playload. Today the take-off weight was 6kg. max  take-off weigh is 8kg and min is 4,5kg. Currently I have mounted 6 t-motor 4012-400 with 15x5 carbon props at 6s(22.6v).

I have less vibrations on apm and gps/compas module because motors and props are very balanced. The Apm is mounted with all other electronics on a separate rubber isolated layer. Also this layer hold the separate battery for powering the apm and other electronics. this mean this layer brings a lot of mass against the mainframe with their heavy main batteries, motor mounts and esc s. This is generally god against vibrations.

My accel log:

simple hovering is between 70 and 90 seconds in log file. all other is starting landing and some throttle tests.


So i try to find the problem in main settings. And here especially for THR_ALT_I / P.

MP defaults and currently unchanged settings for THR_ALT_P and THR_ALT_I are

THR_ALT_P = 1.0

THR_ALT_I = 0.0 .

Did i have to change this setting? Is this the problem? Currently i am unsure because the wiki only talk about 2.x firmwares. http://code.google.com/p/arducopter/wiki/AC2_AltHoldMode

greetings wolke


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  • The same happened to me, and I solved it reducing the LOITER PID to 0,5 as Randy recommended in the 3.0.1 post :

    ''Warning #2: GPS glitches can cause sudden and aggressive position changes while in loiter mode.  You may wish to reduce the Loiter PID P to 0.5 (from 1.0) to reduce aggressiveness (see image below of where this gain can be found in mission planner).''

  • hey :(,

    second alt hold test today. same result:(.


    • starting in stabilised mode and climbing to 20 meters hight
    • hovering stable at 20 meters. throttle stick is ~47%
    • switching to alt_hold mode
    • motors nearly cut of and copter  fall around 6-10 meters
    • quickly switching back to stabilised mode and throttle up to hold the copter

    while the copter was falling i noticed no changes in throttle. the props nearly stops during the period as alt hold was switched.

    in moment all settings for throttle are default values. i really need some help here because i do not really understand the instructions and/or the background theory behind for tuning this values. http://copter.ardupilot.com/wiki/altholdmode/#Tuning

    greetings and thx in advanced


  • Wolke

    The same is happening to me - see my recent posting 'motors cutting out when testing'.

    I have been upgrading firmware for years and have the latest MP 1.2.83 and am trying -r4.

    I never had this problem with"stable" 3.0.1 firmware.

    Maybe it is some setting in MP 1.2.83 ??????????

    If I switch back from either Alt hold or Loiter to Stabilize then all seems OK????

    Not game to fly until this is resolved

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