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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It was a Spektrum DX8 - it's a uDrones Quad (originally RTF - though I have since taken it apart to learn more)

I am also a rookie - started last year with an AR.Drone modified for R/C, built my DIY Hex and continued my flight training (AKA Several crashes).

I haven't tried the iPhone vibration app yet (a live graph of the raw accelerometers over USB would be really nice - hint-hint development team).

I have not tried 2.9 yet.  When 2.8.1 was released there were lots of "flies great" posts on the forum, but with 2.9 there seems to be a whole bunch of tuning issues.  I plan to wait for the 2.9.1 release.

My APM (2.0) is hard mounted to my frame and it flies with 2.8.1 pretty well.

apparently this new version is  buggy..what a pitty!

Hi Marco, I am downloading log files now, but there are a lot of files. Not sure which one I need, I'll see if I can figure this out and then upload.


The Quad did not response to any input, throttle stick or other. It was truly autonomous (sorry..bad joke) but not the way I wanted.

And AR8000 receiver

I wouldn't say "buggy", but ambitious and untested over a large population of configurations.  If there were a bug, it would affect everyone with the same hardware configuration.

Where is your throttle stick when you are in Alt Hold?

Well, here is a "flies great", really great in fact, only Loiter is jerky, but for me v2.8.1 had that too.

Spent a little time tuning RATE_P, I & D this afternoon and it is now very, very good, no more wobbles on descent and in calm air I can take off vertically and do not even have to touch the sticks for up to 10 secs, could never do that with v2.8.1! Try it Stephen, you can always go back to v2.8.1...:)

Thanks Randy, yea it's the waypoint speed that scared me some a little yesterday when flying at home.  Was that not slower by default before?  I'll slow it down to 2 (can I put in 2.5?) and retest today.

I agree Stephen, the group of testers has made thousands of flights from 2.8.1 to 2.9 final without this "complete loss of control".
During my tests I always have the notebook with the 3DR Radio connected, if the tx/rx fail I can always give a RTL/Land with the planner
in emergency, but I've never had to do it.
A single crash does not necessarily mean bug, 99% of this fail we found that it was a hardware problem... but all is possible, then now wait for the log.
About the bouching during alt-hold try watching this video, two of my hexa in Loiter, you see them bouncing? :-)
The implementation of the inertial navigation for alt hold has certainly introduced problems related to configurations with a lot of vibration (unbalanced props, etc.), that is obvious, this involves a tuning most appropriate for all the different setup.


My throttle stick is by 50 %, if I activate Alt Hold. And from there , I don´t touch the throttle stick and it´s fall more and more :(.

You can push the stick up to stop the descent but it shouldn't descend at all, as soon as I hit Alt Hold there's a very brief drop and then almost perfect hold, are you using the default params EK?

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