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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Not sure if anyone else is experiencing this, but having uploaded 2.9, calibrated the accelerometer etc.  When the Hex is connected to MP via USB, I see quite a lot of movement on the artificial horizon despite the Hex sitting perfectly still on my desk.

I have included the below video capture to illustrate this issue.

Is this normal behaviour ?

Did you mean version 1.2.30 from the downloads are as I can't see v1.2.32.  My auto-update is currently showing v1.2.31.

Thanks for the tip...

I will give it a try and hope that it fixes the rapid oscillation Loiter and Alt Hold modes.

But, where do I go in the Mission Planner to change the MPU6K filter settings?

I setup level used Bottom spirit level and command level in terminal is Ok. (old method)

It's an APM2.0, and I tried a lot of things, erase methods of v2.5.5 (PageErase), v2.6 (ChipErase) and of course 2.9.0 (BlockErase). 

I tried also to remove and put back the dataflash with a small piece of paper on the top of dataflash to have better contact.

Each time after those operations, it's the same problem, new logs have negative numbers.

I'm running out of ideas :)

Try with "AHRS_GPS" disabled.

Auto-Update makes from MissionPlanner-1.2.19 MissionPlanner V1.2.32.

I noticed the same on my quad...

It's under "Advanced", you have to scroll down a little. The default parameter is "0", which is 42hz filtering... a lot more sensitive to vibration than 20hz.

Not repeatable... I was running 1.2.31 since I started MP and it auto updated yesterday. After reading this, I hit the "Help\Check for Updates", and it still came back with 1.2.31.

Just tested MPU6K set at 20hz and it's still bouncing rapidly up and down when in Loiter and Altitude Hold modes. 


Also, tested at the following MPU6K settings:

Set-point             Results

10hz                    bouncing up and down, keeping its position

5hz                      bouncing up and down, keeping its position


Francis, have you lowered THR_RATE_D? That's an important part of this equation. Try going back to 20hz and lowering D. You might also be able to use 42hz if you set D low enough... depends on frequency and amplitude of your vibes.

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