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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  • Maybe a stupid question to developers.
    The loiter speed is default 0,200 = 25cm/s.

    How can all this "fly away" appear in so much higher speed?

    During testing period (could be long) why not have a kind of maximum speed (like slow) so these fast flyaways would be more slow motion.

    And what about a kind of limit on one direction and than trigger direction the opposite way, and so on?
    Also an absolute altitude limit.

    When final release is ready i think i still would prefer the above ;)

  • Moderator

    Just flew v2.9.1-rc2, most things seem well although it was only a short flight, will test more tomorrow. Did have one anamoly but am not sure if it's specifically rc2 or something else. I was checking stick response and at one point the quad seemed to "lose" or not update the right rear motor for a fraction of a second which caused the quad to jerk backwards and sideways for that split second but it reached 38° and then corrected itself.

    Log Attached:

    2013-02-01 17-38 41short.log

  • Leonard. Thanks. So you suggest to erase logs and EEPROM and reset before I install any revision. That's what I do but my quads are overpowered DJI 450 so I change about 12 parameters manually. Thanks! JEFF
  • I suspect many people fly like me, with a PC nearby indoors logging, but not visible or audible. I turn my PC speakers way up and open the windows just to keep track of mode changes and battery levels.

    Does anyone know of a simple device to get PC audio into an earpiece ideally up to 300mts? I guess like a walkie talkie.

    If that were possible, more use could be made of MP speech warnings, adding things like GPS warnings. There should also be a reasonableness check for if the APM is naving to anything over 500mts away.

  • Developer

    2.9.1-rc2 (release candidate #2) is now in the downloads area.  Sincere apologies to those who just started testing rc1 about 24h ago but there were two further issues found that we wanted to address:

    1) small correction to manual throttle scaling using THR_MID (was scaling from 0 ~ 500 at low end when it should be mid throttle ~ 500)

    2) bug fix for longitude scaling being incorrectly set to 1 because it was calculated using the Next Waypoint instead of Home

    3) ESC calibration changes to support Simonk firmware (not critical but very low impact change)

    Improvements over 2.9 are:

    1) resolves "ppm decoder false positives" bug that could lead to RTL triggering even when a radio failsafe event hasn't happened

    2) THR_MID parameter added to allow users to adjust the manual throttle so that vehicle hovers at about mid stick

    3) bug fix for autotrim - roll axis was backwards

    4) bug fix to set sonar_alt_health to zero when sonar is disabled

    5) capture level roll and pitch trims as part of accel calibration

  • Hi,

    I flied my Y6 about 1,5m-2m height at home. And sometime, it automatically landed for unknown reason. I was disable battery fail-safe. Could someone tell me why? I happened to me 2 times. The code is 2.90.



  • Took me a long time to get CLI to work over 3DRadio.

    Turns out CLI via 3DRadio ONLY works if it is the first thing one does after powering up APM 2.5 and setting baud rate to 57600 and the COM Port for USB 3DRadio then clicking on Terminal tab in Mission planner.

    Great, except Log Download does NOT work.

    Once finished using CLI via 3DRadio one must disconnect Mission Planner AND Power cycle APM 2.5 else nothing ever connects again.

    Can Log Download be fixed so it does work with 3DRadio.

    Can a more elegant Exit be done so that Power cycling APM 2.5 is not required to exit after using CLI with 3DRadio.

    Another issue that needs to be fixed, many forum posts from people who cannot boot APM 2.5,  Alive LED On but no blinking LEDs and no boot.

    Turns out the reason is they were connected via 3DRadio and switched off APM 2.5 without first clicking Disconnect in Mission Planner, Mission Planner because it remains connected to the Ground Station does not know the 3DRadio link is broken.

    Solution to 99% of APM 2.5 won't boot is click Disconnect in Mission Planner.

    Mission Planner disconnects automatically when USB connection is broken.

    Surely Mission Planner can detect when 3DRadio link is broken and Disconnect automatically. Would save a lot of confusion, cut down on the number of perfectly working APM 2.5 boards returned because they wont boot when in fact nothing is wrong with the board, Mission Planner has not disconnected from 3DRadio and prevents APM 2.5 from booting UNTIL one clicks on Disconnect in Mission Planner, then it can boot..

  • Moderator

    Just been watching my GPS after startup, 3D lock was reached fairly quickly with the default mediatek GPS. Number of sats ranged from 7 to 10, but look at the distance to home: 10739500! The red dot is my home. Even with 10 sats that did not change much. It's now at 10739440 after 10 minutes. The wander of the GPS track (yellow) is alarming too especially considering the number of sats.

    Click to enlarge:

    3692606299?profile=originalEdit: the only way to set Home to 0 was to click Home Location in the Flight Planner.

  • ok..there is new GPS module


    (it have all the new things it must be there possibility to use it with APM2??

    price is ok...

  • List of strange behavior in 2.9:
    - (Auto) Restart after third point? Mission Why?
    - When Switching to RTL mode, the hexa speeds off to an unknown (the same happened to Marvins, Willie Botha, Richard Boyhan, James W Powell, Jeff Cook, Vijay Singh, Dave Wilkeson ...). I have the hexa thanks to a miracle.
    - When trying trigger the camera throught RC5, 2 motors started to spin (slow)
    - When trying trigger the camera throught RC8, does not work, too.
    - Camera trigger worked through RC10
    - Modes in MP and APM do not match. For example RTL in APM shows acrobatics in MP.

    Many Thanks for all your work. Really apreciated.

    Ps. It´s a bit scaring to fly with 2.9. Is it possible to downgrade APM with the last MP?

    Thank you.

    Ps2. Sorry for my english.

    Ps3. I attach telemetry.

    2013-01-29 13-54-56.tlog

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