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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The ppm encoder is not inside the 2.9 firmware, is another little Atmel, you must upgrade your ArduPPM with this one.

When I performed the MPU6K test, each test was performed with Thr_Rate_D set to 0.004

You may have to go lower; 0.004 just happens to be the highest I could go on my quad. Maybe try starting at 0.001 and work your way up in 20% increments until you just start to see the rapid surging, then reduce about 10%. As Marco suggested (I agree), the default values are suited to larger more massive multicopters. I had to be brave with experimenting on parameters for my small powerful quad; I ended up fairly far from the defaults.

Thr_Rate_D, from my experience, is independent of other alt hold parameters. In that respect, Tuning Thr_Rate_D for alt mode is very similar to tuning Roll_Rate_D for acro mode, as discussed in Dave C's wonderful tuning guide.

Thanks for the insight Dave. ;)

it will go to ver 1.2.32, you could probably do a manual update too under help page on MP.


I have this exact problem with my 2.0 it started a few days ago - I mentioned it in the dev discussion but let it slip as my 2.5 was on a much better frame, so I've been using that.


Sometimes logs work ok, other times it tells me i have 247 logs and they start at -257 and work up. But you can't actually download them.


I also had a dataflash error, but only once. Tried takgin card out etc too. No joy.


As soon as I'm finished my 2.5 build I'll get the 2.0 up and running again and try and get more info.



LOL, ok ok  i though someone might say that - I hadn't actually intended this to be the final video, but got too busy, the music version was just to show mates really


I've reposted it with out music - but you have to put up with me rambling on!


The motors do sound great in ACRO though :) It's just silent in the the fastfoward bits.


RANDY, if you can swap the video out, maybe the one without music would be better! Thanks :)




Totally agree, the default RTL should probably even be tail pointed towards home, with an option to keep its orientation when RTL was inititated.


It's something that need high lighting in the mission planner really as it can, and has, caught people off guard.


I actually love the turn to face home, it's the way I always come home so I'm used to it, so please leave the option in, but it is certainly not for the faint hearted or beginner.


Sometimes i even have my home point way behind me for safety, so nose in return is much easier for me to get my head around.

Last problem, my APM 2 isn't working anymore because of the dataflash, so I had to disable logging via #define LOGGING_ENABLED DISABLED

Because of the bad weather I didn't had the time to test 2.9.0, so I would like to share an experience I had when flying DJI Naza, that we may also occur with v2.9.

Naza come with a plastic case, but this case is not sufficient, when you are flying and sun is low in the sky. Because baro sensor is light sensitive, yawing your copter may lead to altitude drop, maybe 1 meter.

To solve this problem, I had to put a dark plastic box on my Naza.

The black case for APM2 seems to be a little transparent, so this problem may also occur

hi ive lost all power to my 2.9,it will only power up by usb,it was fine am using the apm power supply lead any ideas please,Marty.

managed to flash mediatek this morning, no need to recalibrate, just reload the old params..

fly tested this morning with alt hold on, doing some between and under the trees walk by, and under cables..

seems like the gps got better accuracy..

great release gents, thanks for all your hard works..

Martin, you're posting in the wrong thread. This is about the 2.9 software, not hardware. 

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