ACRO bug (fixed in 2.9.1b): while doing flips in ACRO mode, if you switch to Stabilize while inverted your throttle will go to minimum.  To regain throttle control you need to switch back to ACRO then back to Stabilize again (i.e. switch to stabilize twice).  You never lose control of roll/pitch/yaw.

Loiter/AltHold/Auto/RTL bug: if you switch into these modes with throttle at zero motors will go to minimum until you raise the throttle.

Auto mode altitude bug (fixed in 2.9.1b): setting a waypoint altitude greater than 320m over home altitude may wrap around and instead be interpreted as a low altitude.

ArduCopter 2.9 is now in the mission planner and the downloads area!

The major improvement is we use inertial navigation to improve altitude hold.  This increased reliance on the accelerometers means you must do some additional set-up before flying:

1. Perform the new accelerometer calibration in the mission planner (video).  The auto-trim metho has also changed (video).

2. Add vibration dampening foam between your frame and the APM.  Some suggested materials: DuBrogelhk foam.

 3. If upgrading from 2.8.1, modify the throttle and altitude PID values:

  • Increase your Throttle Rate P, reduce I to zero, increase D
  • Increase Altitude Hold P, reduce I to zero
  • Tune Throttle Accel P and I terms but try to keep P about 1/2 the size of I


Here is the list of major changes (a more detailed list can be found in the release notes):  

  • Alt hold using inertial navigation (Leonard, Randy, Jonathan)
    • AUTO_VELZ_MIN, AUTO_VELZ_MAX parameters control the max climb/descent rate for the autopilot (cm/s)
    • PILOT_VELZ_MAX controls max climb/descent rate for the pilot (in cm/s)
  • Landing improvements (Leonard/Randy).  Copter will descend to 10m or until an object is sensed with the sonar.  Then slows to 50cm/s descent (speed can be adjusted with LAND_SPEED parameter). (video).
  • Surface tracking with sonar (Randy/Leonard).  Copter will attempt to maintain current distance from objects in front of sonar regardless of altitude.  Only used in alt-hold and loiter, not used for missions.  Sonar can be enabled/disabled with CH7 switch. (video)
  • Failsafe improvements (Randy/Craig/John Arne Birkeland) including bug fixes, additional check for PPM encoder failure and implementation of battery failsafe.  Set-up instructions are here.
  • Mediatek gps driver accuracy improvements and use of SBAS [Craig].  Instructions on upgrading your mediatek to firmware 1.9 are here.
  • Traditional Heli improvements (Rob) including (a) bringing heli code back into the fold, (b) enabled rate controller (previously only used angle controllers). (c) fix to rotor speed controllers - now operates by switching off channel 8.  (d) allow wider collective pitch range in acro and alt hold modes vs stabilize mode  (e) bug fix to allow collective pitch to use the entire range of servos
  • Acro trainer (Leonard). Copter will return to be generally upright if you release the sticks in acro mode.
    • ACRO_TRAINER : set to 1 to enable the auto-bring-upright feature
    • ACRO_BAL_ROLL, ACRO_BAL_PITCH : controls rate at which roll returns to level
  • Camera control improvements (Randy/Sandro Benigno):  (a) AP_Relay enabled for APM2  (b) Trigger camera with CH7 or DO_DIGICAM_CONTROL command  (c) Allow pilot override of yaw during missions and fixed CONDITIONAL_YAW command.
  • PPM sum support for transmitters with as few as 5 channels (Randy/Tridge/John Arne Birkeland).
  • Performance and memory useage improvements (Tridge).


As per usual PIDs are optimised for the 3DR/jDrones quad with 850 motors and 10" props. If you're using more powerful motors/props and are seeing bad flight behaviour in stabilize, start by turning down Rate Roll P in 25% steps.

Special thanks to our testing team lead Marco and the dedicated bunch on the 2.8.1 release thread who put their copters at risk while testing the pre-release version.  Some of their videos are here: 1 2 3 4 5 6 7 8

Please feel free to report issues you find in the discussion below and/or add them to the issues list.


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Yeah. Same here, but nor the last 9 years, but 3. Those multirotor have a relaxing flight. :)

1) A fast crash- I wonder what happend in here?

Video: (starting at the crash)

Also at 48s you can hear a sudden burst & roll direction change. That was caused by FC.

My take on the video + logs would be that crash happens after 4800.

Trottle IN goes to min = I tried shut down motors.

Throttle out goes to max = reason why motors spin even on snow.

Unfortunately I can not tell more from the log.

Does this imply FC malfunction?

Left back motor did not work after I took it from snow. Esc was wet so it might be caused by the crash, not the reason for the crash.

Also the roll- value goes very low after the crash (the crash as a very fast roll spin)

Does this mean a sensor failure on roll --> fast rolls pin?

Attached is also the log.

2) Alt-hold climb

My hexa hovers at quite high trottle. This might be the reason for climb at alt-hold.

My hexa has good alt hold when i move thorttle to mid stick, but if I hold the throttlle at normal hover throttlle it climbs.

Is there a dead band in trottle at alt hold & if one really puts high trottle the hexa climbs?

--> one needs to have trottle around mid stick when alt-hold / one is able to control alt with throttle even at alt-hold, but the dead band is quite broad.


Hi Leonardthall.

Here is my log file.  It was a bit windier than the last time I flew and my quad was very wobbly even on gentle gusts of wind.  I tried increasing and decreasing my Rate_I but it made no difference.

Please can you have a look at it and tell me if you can spot anything obvious or any suggestions that you might have?



video looked identical to a motor/ESC failure on a quad to me, you would need to see the individual motor output to confirm but the fact you found a ESC/motor not working afterwards pretty much confirms it for me.......


to your secound point, if you move the throttle postion more than 10% above mid point in Alt Hold mode (say to your normal postion you need to maintain manual alt hold) the quad will climb. There is a dead band there. So once you hover and change to Alt Hold mode you need to return your thrrotle stick postion back to the mid point if you want it to stay level.

Decoupling the motor mounts is a tricky thing. Look at audio-equipment, the higher the preassure is and the smaller the touching faces are, the less vibration comes through.

This of course does not prevent you from vibrations, the motors/props need to be balanced well and the motors should run calm.

I also think that it looks like a motor/ESC failure. However it is interesting that the reason your motors didn't go of is because you were in return to launch. So you may have been in fail-safe for some reason.

I do not know how to install version 2.9
In Mission planner is always displayed 2.8.1: (

Congratulation, your accelerometer noise is quiet reasonable and your alt hold is plus or minus 20 cm from it's desired altitude, even with your sonar jumping up and down. So I would suggest that you turn off your sonar and make sure that everything works properly.

Then you can work though making sure your sonar is working well.

Good luck,


Turn on INAV before you do your test so you can include the logs. But I agree with Marco, it is probably just tuning if you have a powerful copter. Try to keep a ratio of 2:1 between I and P.

Good luck,


Thomas, update your mission planner and it ll appears.

You can't compare audio gear with the copter prop vibrations.  In audio gear you are intentionally generating the vibrations and you want them isolated from their mount to keep them isolated from potential secondary radiators, like a wall or tabletop.

I agree that the best thing is to eliminate vibration at the source.  Adding padding or other isolation methods could introduce sympathetic harmonics that you won't be able to tune out.

I am worried about all this chatter about vibration that the goal is a finely-tuned multirotor that is on the edge of instability and performs aerobatics like a hungry bat.

All I want is a stable platform to carry a camera to altitude.  If it takes a second or two to settle on a loiter altitude, that's fine with me.  If the controls are a bit sluggish, that's fine with me.  A rock-solid altitude-hold would be great for aerial photography or video, but not at the expense of a stable platform.  Since I plan to hang thousand-dollar cameras under my hex, I want stability - not performance.

+1 !

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