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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Which APM version board are you using?

Randy, Thanks for the reply. I ordered an APM with the ublox a couple of days ago and wanted to make sure.

I had the same effect. Must install, uninstall and install again. After the update, it was V 1.2.32.

You might be looking for a ppm update. Check out the APM wiki when you get a chance.

That's right Balloon, but try to tune better the crosstrack gain.

I don't know.What should increase or decrease for tune crosstrack gain. You can explain for me please ?


Hey Graham,

I've been tuning and tuning. I can't seem to tune out the Loiter and Altitude Hold modes jerkiness too... Pretty frustrating.

I've played around with the Stabilization Angular Rate Control settings, the Stabilize Control settings, and Loiter Angular Rate Control settings. I've adjusted 25% up and down the scale, and the changes that I made doesn't seem  to affect or show any signs of  the rapid oscillation (jerkiness) going away in Loiter and Altitude Hold modes.

Thanks in fact i have updated as per the instruction with flip. But just wanted to know if this new version has the updated ppm or we still have to flash the hex file.

I had the exact same problem, the motors rapidly surging in alt hold and loiter with 2.9. I think the cause is excessive vibration making it to APM; that was my problem anyways. Lowering Thr_Rate_D to 0.004 and changing the MPU6K filter to 20hz fixed it for me. I think the best way is to first work on isolating vibrations; use ACC RAW data flash logs to find the best mounting method for your rig.

Thanks Chris, I will check that out tomorrow.

I tried again today, before i read your reply....Got it to 10mtrs altitude, put it in alt hold, and it dropped 2-3 meters fast then went up a meter , then down, up, down , up ,etc...etc...

 It is like a yo yo !. But in Stab mode it fly's fine. 

This's my PID last setting.

I flew for around 10-20 seconds before going into alt hold, but not a steady hover, as there is not a big distance between elevation and decent with my throttle stick, although I changed Rate roll P to 0.90 today and the quad was smoother. Alt hold turned it into a Physco  Yo Yo.  I will upload some logs for you ASAP. I have a busy weekend. I loaded 2.9, but I did not Reset the APM manually before.

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