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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Graham, does it straight out if you ARM? That would set home.

I suppose you could set home with the MP too. 

I am relieved to know I am not the only person to have runaway 2.9. My copter is a total loss but will rebuild next week using a DJI 450 frame. I am going back to 2.8.1. I had over 30 good flights, including 5-6 waypoint missions and autoland. Even my wife could fly the thing ! I usually switch to stabilize about a 1 m up and land it manually. I really did not expect 2.9 to be so unreliable. I am now going to follow the same procedure I use with Windows updates - always wait for 6-8 months until the version stabilizes and people figure it out.

On a separate topic - has anyone in this forum used the Wookong flight control system ? It is very pricey - $ 1000 - $ 2000 depending on features but a good copter is not cheap either. Might win the lottery though ..

 - Vijay

Hello Randy,

Please, could you clarify what is THR_MID scale (percentage, pwm, ...)?

Another question: Since I have an overpowered quad I have changed my THR_MIN to 1 (default is THR_MIN,100).

Should I continue using this parameter to get a near middle stick hover or should I use the default 100 and use tune THR_MID?



I believe that crazily large number is because your mission planner's home position hasn't been set.  I'm not sure where it's defaulting to but it must be a long way away.  If you go into the Flight Planner screen and click on the "Home Location" link it will update.

The thing which many don't realise is that there are actually two "home" positions.  There's the one that the mission planner holds and then there's the one in ArduCopter which it uses for RTL.  I believe the DistToMAV that you're displaying is calculated within the mission planner and tells you the distance from the MP's home to the copter's current location.

I'll ask Michael O to change it so that the mission planner retrieves the home location from the copter itself.


By the way, "Dist To WP" that appears as massive numbers (65535m) until the first waypoint has been initialised.  It's a display issue and it's sorted out in 2.9.2.


I see that my GPS and MP exhibit the same behavior. I did see Randy's post about the DistToMav being fixed in the next release, but the GPS track or "bread crumb" trail going nuts has me worried.

I've even updated the FW and mounted my unit on a pedestal similar to the NAZA and still same results. Makes flying and testing in my neighborhood nerv-racking when in LOITER mode.


     It's getting late in Tokyo again so I won't be able to complete the investigation until tomorrow but this line from you is very telling: Modes in MP and APM do not match. For example RTL in APM shows acrobatics in MP

     Just from looking at the KMZ file it's clear that you were not "speeding off in RTL mode".  You were speeding off in ACRO mode.


When I look at the details of your flight modes vs your channel 5 switch it appears that the sudden switch to loiter was because the CH5 flight mode switch momentarily changed to about 1550 (position3 = loiter).  If you didn't actualy command this I wonder if perhaps you have a radio problem.

     After being switched into ACRO mode, your copter does temporariliy go into RTL before reverting back to ACRO mode again.  Did you send a command from the ground station to switch it into RTL mode?

Anyway, the most important thing is to figure out what the issue is setting up your flight modes.  Where are you seeing ACRO when you think it should be RTL?  Are you looking in the Flight Modes screen of the mission planner?  Could you make a screen shot to explain more where you are seeing the difference?


     Really though, this is nothing new to 2.9 right?  There no question that the GPS position will move around a lot especially if you're indoors and/or before you have a 3d lock.  That's nothing to do with the arducopter software, that's the GPS.  It's been said earlier in the thread as've got to wait for a 3d lock and then you should wait another 30 seconds or so to let the position settle down.  The UBLOX is a great GPS, check-out your iPhone or other gps device and see how much the position moves around..if it doesn't move then the device is simply hiding it from you.

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..


     I see you're relatively new to DIYDrones and I know it can be daunting but I've looked through your postings and it doesn't appear you've made any logs available for anybody to have a look at to help diagnose your issue.  From your description of your quad climbing into the sky when you engaged alt-hold it sounds like your issue is that you don't have enough vibration dampening between your APM and your frame.  Did you read and follow the instructions at the top of this posting?

I'll try again abit later, but with 10-12 sats locked and sitting there for a few minutes in a open field, I'm hovering 15-20 feet off the ground trying to stare at my laptop and I'm seeing those results.

Is there a way to dampen the amount of GPS filtering? So it's not so sensitive?

Sorry to sound like a noob, I'm just trying to get through all the massive list of parameters!



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.




     You were in alt-hold mode or loiter I guess?  The throttle deadband is smaller in 2.9 so maybe you just had your throttle below 400?  If you do that it will very slowly descend and land.  Make sure your throttle is in the middle and you won't have the problem.  In 2.9.1 we're planning to allow you to adjust where your hover throttle is in manual modes so you'll be able to push it up to the middle so then when you switch to alt-hold it'll already be in the middle and you won't have to remember to push it up into the middle.  You will have to adjust that parameter though at least once to adjust the deadband.

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