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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Norman, I like that you have your motors under the arms (at least it appears that way). That's eight less "impacts" on the frame per revolution!

got a little problem right now, my tricopter always try to roll to the left..

i've check for any hardware problem, switching motors and esc but nothing helps..

i've done recalibrating accel and compass, also not helping..

i hope someone could help me with this.. attached is my log and param..


I noticed in the video that the cone shaped holders were pushed in on both sides of the PROP.

All the APC propellers that I've ever bought have an off center hole on the front side, that's where the plastic gets injected (the spru) and it is drilled afterwards. (Those holes always look ugly)

The hole on the back side where the insert ring goes,  is created in the mould and it is true to center.

Anyways my point is that when balancing the propeller, the cone side of the holder should go into the back side and on the front side of the propeller the flat side of the cone shaped holder should be pressed against the propeller.

This is also how the propeller centers itself in the collet when mounting it on the motor.

By front side I mean the side with size markings.

Those may not be APC propellers in the video, however.

Hi Andre nice to hear another South African been playing with drones few months now still lots to learn used to live in Durban fly helicopters for many years now just nice to play with something different how far have you got with your drone

I agree with most things there but strongly disagree with the "mount hard" part at least when it comes to the APM.  An APM flapping around is not good but hard mounts to the frame are also not good in my experience anyway.

I've brought up the naza approach with the 3dr hardware guys.  I'm not sure if they'll go that way or work on the case so that the whole board is more isolated...anyway, i passed on that information.

Try using the trims on the Tx, it's not recommended but works fine otherwise do the autotrim procedure -

Thanks Chris

Is it something to do in MP to be in Auto Cal ,

I will try what your said.

It would be nice if there was some kind of "motor balance" mode. Basicaly a mode where you can choose which motor to run, and then read out the accellerometer data in the missionplanner.

I agree with John for the motor mounts point. I tested an aluminum boom with a mounted motor using various materials between the boom and the motor trying to isolate it. The results from seismograph (iphone app) was that the less vibration came without any elastic material under the motor....

Hi George,

Been flying planes, helis, 50cc's and everything else I can strap a motor to for about 9 years now, but only bought my APM1 about 18 months ago.  I dont get much time to test and when I do the weather is either bad or a new firmware has been released, and then I have to start from the beginning again.

Managed to fly v2.9 on my quad last weekend and it's the best I've ever seen it fly, especially in alt_hold.  Once I've got the loiter tuned in then I will upload some waypoints and give them a try...

Hello guys! Thanks for the nice job! I do not know if this is discussed in this thread before, bit I realized that in mission planner/flight data/quick, the altitude is based on barosensor instead of sonar. I checked that the sonar is enabled and in the CLI it gives me numbers. So, why in the "quick" the altitude is not taken from the sonar? I assume that with the new 2.9 code, the sonar may be used for other purposes and not for altitude measurements. Is that correct.

PS: in previous versions of arducopter I had very solid altitude hold and loiter based on sonar.



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