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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I think mine is .196 if I remember correctly. Flies great. 

Make sure you dont have Ch6 assigned to some tuning parameter. Its a possible ‘gotcha’. There should be a warning that Ch6 (or 7) is already doing something when you set up a gimbal. Also if you have to reverse the gimbal it will also reverse the tuning effect – even if you disable the gimbal again.

Thanks Bill.  I'll keep going on it and report back.


"Z" axes means vertical movement. I believe it is normal to have Z as different values, comparing to XY.

I have the same problem. Mine wants to go off to the left. I have done the calibration really carefully a number of times but still not actually level. When flying it just stater drifting away if I don't give it a fair amount of stick.

This platform's a s***ton of work, but oh my lord is it worth it :)

RTL sorted out, RX failsafes confirmed working. RTL initially set to 1m/s because I terrified I might lose it.  ALT hold and Loiter all checked out.

No more tuning - time to FLY

I had a weird event towards the end where my home position changed.  I have to check my magnetometer offsets because my flight controller is literally an inch away from a 4-1 ESC...but otherwise - everything worked 100%

Thanks, I won't worry about it then!

They definately have a lot of work to do before the next update.


Yeh, the rate values for pitch and roll are heavily dependent on the power of the motors/propellers and the weight distribution of the copter. I find the 3DR quad values tend to be too high for many other copters.

So the short answer is tune for what feels right on your copter, especially on these parameters. And in most cases lower is more stable/safer.

Thanks for the link Lito :)

But my blog post covers it pretty well. Basically it is because of the maths behind the way we define position in space. I am hoping to get a proper ACRO mode into the code in 2.9.3 ish.

Thanks Lito and Leonardt. I am looking forward to 2.9.3 then. There is plenty to practice btw.

Interesting. I am a bit sceptical that an MPU with 20HZ LPF on acc and gyro on a flightcontrol with cycletime of 11ms can rival acro of the cheap boards for sport/trick flying. To achive that every unneccessary stuff must be turned off when switching to acro and back on when switching to stab mode..  ughh. That's a hard job but i will embrace any progress in that area!

Cheers Kraut Rob

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