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.


You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –


  • My GPS problems are solved.  The Spektrum TM1000 telemetry was interfering so it has been removed.  I also had it mounted too close proximity to the GPS.  The GPS is now mounted on top of a 3/8” diameter carbon fiber rod and is positioned high above the APM.  The 900 MHz telemetry is mounted on the opposite side of the Quad form the GPS down low on the landing skid.  I use a ¼ wave antenna made from stranded wire instead of the rigid plastic antenna furnished with the unit – better for crash I think.  The GPS now allows a solid Loiter as soon as I lift off after short waiting period for the GPS LED to show a 3D lock.    I woke up at 4AM this morning and thought it would be a good idea to fly the Quad - 60 YO man flying his toy in the middle of the night.  I’m having a blast with this thing.

  • Hello,

    I use v2.9.1-dev, make level und do Radio calibration. All OK.

    Now I turn on under Hardware Optflow and sonar, then set CH7 to sonar.
    Disconnect vom MP

    Try to connect und now I get no Mavlink connection.
    Can anyone understand?

    Regards Peter

  • Post Blog Rejected: RC Helicopter Kills Toddler in Malaysia

    Hi John,

    It is the mission of DIY Drones to only promote the positive side of hobby drones so, unfortunately, your blog post will not be approved. This unfortunate incident has already received sufficient exposure on other web sites.


    TCIII Admin

    Thomas sorry but I think you miss the point here. Firstly this happened yesterday about 30min drive from where I live so how can it be so fast it is now everywhere else on the other web sites? Stuff that happens in Malaysia just doesn't travel out that fast mate!

    Its nice to post the positive side of DIY RC models but people also need to be made aware of the possible dangers of them as well. May be if you post this on DIY Drones it could help prevent a similar type of incident which was the reason I posted it.

    Now how are you going to feel if someone else child get killed and it might have been avoided if you when and posted this article?

  • Hi,

    I am having a problem with land mode with one of my copters, I have 2 quads with apm25's on them. When I switch to land mode I pull the throttle to zero once I see it is bringing itself down, on one copter lands perfectly the other lands perfectly sometimes, at other times when I switch to land mode it brings itself down nicely and touches down, but then it raises its self about 1/2 to 1 foot then drops then repeats, like it bounces. I have t switch to stabilize mode, with the throttle at zero,  to get it to stop I am not sure what is causing this. I know this copter has landed fine in the past (well it still does at times)

     I have checked through all connections, and reflashed it, erased the parameters, I think I did everything I can think of. I will attach a log file that has a good landing on it and a bounce landing on it,  . If someone can take a look at it and let me know what they think it would be greatly appreciated.



    edit: I forgot to attach the log, I will below

  • I have both the GPS status and the ARM with remote LED’s on A6 and A7.  The ARM LED goes solid "on" at arming but begins to blink about four minutes into the flight.  Happens every flight.  I have LED_MODE set to 107.  Any ideas?

  • Moderator

    Just had two incidents of power fade, spiral down and crash, can anyone shed some light on what happened? Battery was fresh, voltage fine - have telemetry on my Tx. Was in stable loiter first and suddenly things went pear-shaped. Tried again and it did it again. APM2 on X525 quad with 20-22L motors and 30A Super Simple ESC's.

    Edit: thought I had a tlog but not, will try get the log from the APM.

  • Randy,

    Can we expect similar performance with that of DJI on 2.9.2 ???
    With due respect to all the developers and testers, DJI is still way ahead... in terms of filtering, smoothness and performance...

    I am asking this because much of the code in 2.9.2 is being re-written.
  • RTH tuning question.

    I have RTH tuned fairly well but I get a slight wobble on the descent at the end. What is the main gain parameter for RTH? Or do just have the basic rate gains slightly too high?


  • Hi guys,

    I need some help please.
    My Quad is flying well, except for one thing. The trottle is way too jumpy. one click up and it rises, lower by one click and it falls. This makes for a very uneven flight.

    What parameters do I need to tune?




  • Another good damper - neoprene. Buy a chain guard protector for £6, and cut/layer to your hearts content. Waterproof too, even if your electrics aren't! :-)
This reply was deleted.


Santiago Perez liked Santiago Perez's profile