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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I noticed when you make changes to "Standard Params", the first time the screen is used COPTER_LEDS is undefined (blank box, no "disabled"). Setting this to disabled before writing prevents the error from coming up. So still a bug, but yeah it's minor.

Regarding that pin conflict between COPTER_LEDS and radio RSSI... is there a fix planned for this? For now I'm using airmamaf's custom code for RSSI+LEDs, but those LED functions are not as fancy as the built in. I think with 2.9 APM is going to see a lot more interest from FPVers... smooth RSSI configuration should be a high priority. ;)

Yeah, all of my heli flying since... maybe September has been with GPS_Use = 1.  I've never had a problem.  The only issues is that when disarmed, the HUD moves around (and the heli servos), but soon as you arm, the HUD will stop moving.

Nice, thanks Rob!

Ive got theMB1260 Sonar do I set it at EZlO,many thank's,Marty.

Loaded 2.9 /      I went through the calibration process with my quad . (880kv motors / APM2 / Ublox GPS / Sonar / ) Rate roll P set to 0.100

 I had the APM set to disable the arming until there is GPS lock. I armed and flew. It was foggy and snow on the ground.

Got it up to around 7m alt, and flicked it into alt hold on its way up. It immediately dropped like a brick. I managed to put it into stab mode, raise the throttle to save it from a very hard landing. Is this something I have done ?

Marco, have you tried landing in auto with the big boy yet? My quad landed on a 15 degree icy slope today and still stayed on it's feet!


That happened shortly after i couldn't find ALT-HOLD_RTL :)


I much prefer the new name though.

I tested it as far as to watch the HUD jump around, not even sure if it was enabled for the 2.9 vid!


I will check and post the param file since i neglected to do so


It was an easy tune though for the bigger motors on a quad. Reduce rate_P to 0.13 and stab_P to 3.8. Everything else stock.

Maybe I can make a heli land on the ceiling? :D

Merci à l'équipe pour le travail:


Trop de mauvais temps,pluie verglas, neige pour tester 2.9 sur mon APM 1.4,Mais je suis vraiment dans l'attente..!

question: je compte actualiser mon équipement dois-je investir dans APM 2.5 ou Attendre encore un peu  pour PX4 ????

 Merci et encore Bravo

Just uploaded this to my tricopter...

Can't wait to give this a try. Whoop Whoop!

Thank you to everyone who was involve with this release, to Marco for making all of the test videos, and most importantly to Randy for replying to all of my newbie questions...

Hi everybody and thank you for your hard work on the new version 2.9 !!

I'm new on APM so perharps it's a stupid question, I got a APM 2.5 and a 3DR power module ,on the setting  BATT_CURR_PIN I've got the choice betwen disabled/A1/A2 or A13 and no other choice possible The A13 pin is already on the BAT_Volt_PIN .On a forum I saw that I should put A12 for BATT_CURR_PIN but its not possible on mission planner .I tried also the values A1/A2/A13 on BATT_CURR_PIN but it gives a bas value (20A with engines stopped !)

I had the same thing on 2.81 and 2.9

Is it a issue or a mistake from me ...?

I can't find the parameter that sets the loiter radius.

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