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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Anxiously awaiting input on this one before I fly 2.9. It seems like if it was a fail safe rtl then it should have landed but it dropped instead and was out of control. Do you have your throttle fail safe set well below your min throttle when you set it up on your radio?

Hi, thanks for finding that. I did not see it.

Very strange. Failsafe should trigger a RTL and not a LAND and why should there be a radio failsafe when hovering indoors 1,5m in front of me?

I definitely switch back to 2.8.1 until those strange issues are discovered and fixed.

Besides that failsafe issue, I am not happy with the alt hold too. It ist much to overacting.

Yesterday, after the frustration with the APM2.5 and the 2.9 FW, I switched to a naze32 I received 2 weeks agoe. I soldered the pins on it, flashed the latest firmware with the mods of crashpilot onto the board, invested 30 minutes in setting all up and put it onto a H.Quad, that did not fly well in Alt Hold with the APM2.5.

Then I walked out in front of my house, and hovered around a little. Then I switched to alt hold and what a surpricse, it works great. No jumping up and down. I even did not notice any little reaction, when switching to alt hold. First I thought I did not correctly programm the switch, as of the APM I am used to see a strong reaction when switching to alt hold. Nothing to see when doing it on the naze32. Such a smooth hovering and such a smooth alt hold. All with default settings. No PID tuning done so far.

I am not sure, if I want invest so many more hours into trying to tune the APM, when there is a tiny little board like the naze32, costing a fraction of the APM, that does such a great job and is that easy to tune.

At the moment I am very disappointed with the APM and I am thinking about selling all of them and switching to other FCs. First I will take a timout and wait for the next release of the FW.

I think 2.9 lands instead of RTL upon failsafe if you are within 15m from home.

But when it wants to land, why did it go up to the ceiling?

And why does the ACC Z cause a failsafe, when I was hovering in stabilize mode?

Even it is not a good idea to land in case of failsafe when within 15m. Imagine you are cruising over a lake and are close to the bank and so within the 15m, but over water. Landing will not be the best idea in this situation I guess.

A little off topic. Since I am very confident in 2.9. Successfully put on 3 small Quads without incident, am thinking of putting on my DJI S800

Does anyone know of someone who has successfully tuned in S800 which, as you know, is significantly larger than my DJI's 450 and 550?

Thanks!! JEFF

rate_p is at 0.155, rate_I is the one I took to 0.45...all is well.

And Acro Trainer...WHY?  Isn't that Stabilze mode?  Maybe without the Accel?  Why not call that out or expose it as a mode setting.

I'll make the change to the setting.  Acro mode is where I fly this thing most of the time anyway.

Any ideas on the loiter?

What is your motor? Low kv with small props?

I'd like it to fly in ACRO mode most of the time.  If I want a stabilized aircraft I'll switch to stabilize.  Seems strange to me that you'd want a stabilized ACRO mode.

Nothing else I fly returns to level when I release the's odd behavior to me...that's why I spent the time trying to tune it away.

DT750 motors rewound to 880KV with 10x4.7 props.

Fairly high performance.

I had a look, it appears to me like your are having a radio failsafe event:

// turn on throttle failsafe if no update from ppm encoder for 2 seconds
if ((millis() - APM_RC.get_last_update() >= RADIO_FS_TIMEOUT_MS) && g.failsafe_throttle && motors.armed() && !ap.failsafe) {

I can't figure out what EV 15 and 29 mean.

CLI stands for "Command Line Interface". It's basically the Terminal mode in the Mission Planner(MP).

What's about my problem? The logfile shows a radio failsafe event. Then it shows LAND. When it should land, why did it jump to the ceiling, then fall down, jump to the ceiling again and if the propsafer would not have been done his work, it would have been jumped up and down, until the battery was discharged..

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