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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James, that sounds like a hardware issue. Might want to check your sensors in the CLI Test menu. 

When I go to CLI - the Blue Light goes off: Here is the message:

load_all took 3992us

AP_Motor: failed to create throttle curve

Press Enter 3 times to start interactive setup

then I get the prompt..

Not sure which sensors to test...

I have started with "ins"


Init Gyro

and just hangs there... at this point the blue light comes on solid again..

The 2.5 case comes with pink foam that is supposed to go inside and cover the baro. It is relatively transparent though; I could easily see the orange serial LEDs flashing through it. I'm sure the pink foam works fine and filters most of the light that would make it in. I replaced my pink foam with opaque black open cell foam that keeps all the light out; not sure if it works better because I didn't try the pink stuff first.

Why not make it so that it will RTL facing the launch point and then when the launch point is reached it will simply yaw to face the direction in which it was armed in...?

Thanks Marco for clarifying this. appreciate it.


    Sure, that's possible too.  I'll add it to the list of options.  That's what I personally do manually after the RTL completes but before i take back manual control.

I'm really shooting myself in the foot here... :/

Since most folks entering our hobby start with LOS flight, I think tail pointing home is more appropriate. FPVers and LOS experts are already digging around the parameters a lot... they can handle RTL parameters fine if they want it to point home.

Had a test flight with 2.9. Only hover + ALT hold.

All works smoothly. Thank you!

I turned the rate P sligtly down. I want the hexa to be rather smooth for video use.

One feature has appeared: When putting alt hold on, the hexa drops 1 meter down and slowly starts to rise up a gain. Earlier versions putting alt hold on had no immediate effect - now it shuts down the motors for 0.2 secs or so. This might be a feature and designed this way, but it is a scary moment when the hexa drops first down.

Talon Hexa, Turnigy 2217, 11x4.5, F-40A Simonk

Did you also had a try after unplugging everything attached to your board ? It could be something wrong with a device connected.

I had a similar problem because of the dataflash, I had to disable logging to make my board working again.

This was a discussed problem but this should be removed, we will investigate.
Try with my parameters set and give me your impression.

Yes, this is another great idea, a drone rotation when reached home.
The "problem" is during RTL, i can understand that the missions would like to have the nose pointed at the next WP (I do not like, sorry, "yaw free forever" LOL) but no when reached home, if a newbie lands automatically and then takeoff the drone would be rotated 180°.

Yeah Robert, we discussed but were not very well make this the default.
I repeat, no other system behaves in this way and I think it's pretty obvious, flying with "yaw free" I always know where I pointed the nose, simple, the last position where I put it, if you look at my video is always in the direction of takeoff.
ArduCopter comes from ArduPlane, which is why we have continued with the concept of "plane" in some automatism, but in this case (yaw) in my opinion is wrong.

With heli and plane is another question, i agree.

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