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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  • Hi Guys 

    Just double checking myself 

    these vibes are within the tolerance right?


  • Randy

    I assume that is your 3dr quad demonstrating the foam pad in the pic above.. I see a GoPro mounting plate on the top platform. Did you have any vertical balance issues with APM2.5 and tuning? I have been pondering a place to mount mine.

  • Hi I am a very new quad flyer with a 3dr Aruducopter kit straight from the box. I apologise if this is the wrong place to post but I have been following the “damping “thread with interest

    . My machine appears to be fine in hover, stabilise, rtl etc but very twitchy in Alt hold. No tuning done yet so default 2.91 values.

    I have attached a log file and wondered if someone could have a look analyse and come back with a few pointers?

    As I said very new and on a big learning curve on flying, log analysis, tuning and everything else!

    Thanks in advance


    2013-03-07 12-47 1.log
  • I am fairly happy with my vibration but am still trying a few improvements.

    I have watched a few videos of drummers using the moongel and they just stick it on the drumskin. As my APM is already on thin foam and I dont want to un-stick it again,  I am thinking of just sticking a piece of moongel to the top of the apm, perhaps with a coin or something on top of that. Easy test.


    This thread is very long and I cant seem to find a definitive answer to this-

    If am using a normal PWM RX is there any point doing the PPM upgrade thing?


    Developer suggestion-

    Is it possible to distinguish vibration from normal control accelerations? If so, what about a self adjusting filter value. I am concerned that a low vib copter with high tuning may become unstable if something comes loose. Even in forward flight the non-axial flow into the props seems to cause vibration.


  • Just adding this to my post from one page back, I went from a completely unflyable bird @5hz in loiter/gps to this by switching to the moongel for vibration dampening.  The video is @42hz and slightly tuned pid's.  Can't believe how big of a difference it made.  This quad was literally thrown together from a ruined Xaircraft frame, beat to hell motors and terrible props.  Vibration dampening really is the key to 2.9.1.

  • I had my first loss of control crash with my 2.9.1 APM2.5 today. Can someone in the know please have a quick look? Basically my radio inputs stopped working and at that point it switched itself from Alt hold into Loiter, then after being unable to regain control or get any response using my RTL mode switch, I powered the TX off which initiated RTL (and then proceeded to crash into the house on the way down after returning (my fault, I didn't power it on far enough away).

    I haven't upgraded the ppm encoder firmware, but I'm not sure if this affects it? I just tested my TX now, and it appears to be working as far as I can see.

    The thread is here:

    And my tlog is here:


  • An idea to prevent vertical or horizontal fly aways.

    Now, I am no code guru but I was wondering if implementing something like this is possible:

    1) Implement something in the code whereupon every quad owner sets his distinct HOVER throttle setting. This will vary from one quad to another but gets recorded in initial setup and stays in memory until the user changes the settings (when the weight changes, bigger battery etc..)

    2) Implement something in the code that corelates baro altitude with GPS altitude and checks for rate of ascent or decent. If the baro registers readings that don`t match or are not close to the GPS readings, switch over to the HOVER throttle setting. This will prevent unwanted rapid climbs or descents.

    A cross check with the other sensors could also confirm if things are out of whack. 

    At least, adding a HOVER throttle settings the mission planner would be a good thing for people to do in their calibration process. It would be the reference throttle setting the APM could revert to if failsafe is activated or things go out of whack. 

    Just an idea.

  • Just wanted to add my 2 cents of vibration dampening success to this.  Someone suggested Moon Gel by RTOM, apparently just about all music stores carry it since it's widely used for drums.  Ended up stacking two pieces on each corner of my apm with super thin 3m sticky tape on top and bottom and my chopper is flying like a dream.  I had to use 5hz before and alt hold/loiter were absolutely terrible still, that's no longer the case and it behaves beautifully at 20/42 on almost stock pids.

    I think I paid $6.40 for 4 pretty big pieces, i only ended up using maybe half of one strip.  It's super cheap, ebay also has plenty but the local convenience with the music store was awesome.

  • Just want to say thanks to the developers, beta testers, folks on the DIYD forums, Wiki’s, and everyone associated with v2.9.1


    My Quad is a Flamewheel 450V2, APM 2.5, 2212/930KV with 1047 props, RCTimer 30A ESC’s (non-SimonK), uBlox GPS, 915Mhz telemetry, EZ0 Sonar installed but disabled, APM Power Module, Spektrum TM1000 telemetry reporting back to DX8, (2) 2200 LiPo’s, and of course v2.9.1 firmware.


    Stability is excellent and Loiter is very good in 12+ winds.  I have the APM mounted on four foam ear plugs for vibration isolation - what a novel idea.  I’m running default parameters with exception of Stability Roll and Pitch are reduced to P=2.5


    This thing is totally the nuts… 

  • T3

    Hi guys,

    So I've had some vibration issues that I thought were really related to a bent motor shaft from about a year of service and crashes. I definitely have a motor that makes a whistle while it flies. The new motors are on order and not here yet, so I decided to see if better vibration dampening for the APM could cover up my problem. In short, yes. I switched from 1/4" high quality helicopter gyro mount tape to the a version of the earplug method. The before and after results are posted below. Now I've got stock settings on alt hold and mpufileter to 20 hz. Unbelievable altitude hold. I'm going to do a blog post tonight outlining the VR reduction setup. I am posting this just so that we can get an idea of what kind of results just a 5 minute earplug job can produce. 

    3692643642?profile=originalThe green line is before, the red is after. Remember: I have changed nothing but how I mount the APM and I have a bent motor shaft. 

    Special thanks to Randy for the diagnosis help,


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