ArduCopter 2.9 / 2.9.1 released

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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  • Does anyone else have a problem of not being able to set the WPNav parameters? I would like to speed the quad up a bit but they seem to be set and nonadjustable? Am I missing anything?

  • Seems the 3.0 rcxx info is spread all over the place. Think we are up to rc5 now so I may give it a go.

    Is there a quick start guide anywhere of things I need to be aware of when switching from 2.9.? (non x.y).


    Will the MP give me the choice of H frames (need quad reversed motors)?



  • Hi,

    i had a small problem today in my 2.9.1b tricopter, i had a sudden drop in alt-hold about 2m while i'm doing a video shoot..

    i had to cancel the entire today's video session because i don't have the guts to fly again until i know what happen,

    theres a lot of cliffs where i had to do the job today..

    attached is my flight log, i hope someone would point me in the right direction..


    2013-06-06 20-15 1.log
  • I missed information on wiki and around(which one is main instructions page anyway??) that Y6 needs to be V shape on MissionPlaner arducopter level page...till now it was X..stupid me i try to left-right commands all messed up... luckily i manage to land the bird down without problems....Firmware V3.0 rc4

  • Hi,

    I am having a problem with a quad with a px4 on it. Althold is not working very well. I am not sure if it is because of the mounting location and air pressure change (caused by the props) is causing the problem or some other noise.

    I am not sure what to look for in the lgs.  I will attach them here.



    2013-06-03 16-32-48.tlog

  • Just want to post my latest experiences with v2.9.1b.

    So far I had over a dozen flights. Loiter, Alt-Hold, and Auto, RTL, Land.
    I have to say I'm very impressed.  Even in very windy conditions in Stab mode, the copter tilts into the wind.

    Auto missions work well. But for some reason the Alt I set doesn't reach its set point.
    For example.  I have WP set to 20, then to 100, then to 20.
    The copter never goes above 20.  The distance between the points was small, maybe 40 feet. But still, I would expect the copter to reach it's set Alt of 100 for the WP, before moving to the next one.

    RTL and Land with Sonar OFF are very good.  I found Land to be smoother on its own, then in RTL.
    I would think they both should work the same way.

    I tried a few times with Sonar climbing up hills and it increased in Alt all the way up.  Although on very windy days the Sonar seems to act up, so had to turn it off.

    The most impressive part of all, is that my copter has vibrations way past its normal points.
    Sometimes hitting between +5 to -30.
    And I can still have confidence in Auto, RTL, Loiter.

    I'm running a JDrones Quad with 880 motors, 12" or 10" props an 3600mah batt.





  • Hello,

    my quad crashed today when switching from manual mode to RTL. The copter started spinning and lost height. The battery was not empty and after rebuilding the landing gear everything is working normally. I will also upload the video from the camera.

    2013-05-28 19-11 35.log

  • Hi,

    I'm looking more deeply into Failsafe settings and how it actually should work. While drawing a flowchart i came up with a guestion:

    Which one of the two failsafes have higher priority, Throttle or battery?

    If i'm running AUTO mission and have FS_THR_ENABLE=2 and also battery failsafe enabled. What happend if both failsafes are triggered during AUTO? Will it RTL or Continue mission?


  • Hi Guys, just following this discussion as I am also having the same issue with an overpowered quad. Thanks for all the hints. I also propped down from 15" to 12 and fixed the problem with stability and weight. It got the rpm's up to the area stability was best. Also, my built in magnetometer was getting affected by induced magnetism from my dc power lines under the apm2.5. Did the mod With a external magnetometer and now is solid without any angular drift on power up. ( I think that was my issue from the start) Going to put the bigger props on as the payload is increased. Testing continues....

    I have an issue with run up and takeoff stability.

    My F330 is difficult to get off the ground nicely i.e. with no pitch/roll manual interaction.

    Once it is in the air, it works well. Alt_Hold also works smoothly.

    It hovers nicely at 419 (from the log) which aligns with around 40% throttle on my DX8.

    The Mod/Stabilize line in the log suggests a hover speed of 320 approx. Why not 419?

    I have left THR_MID at the default of 500.

    Initially, with THR_MIN at the default of 130, the unit acted by a provoked pit bull terrier – sprang into the air and had to be brought down with a total throttle cut.

    I now have THR_MIN at 35. Tests at higher settings did not help.

    How should I approach analysis to achieve an orderly takeoff?

This reply was deleted.


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Aug 25