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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Yeah that z is too high, can you swap out that ferrous? And maybe move the apm up a bit?

I'll do that.  Any idea how/why the compass calibration got so far off?  Is there a bug in the autocalibrate code? Can I turn off autocalibration (is that the auto declination?)

Thanks Dave,

Yes, I'll do both and check the offsets after the ferrous swap, and then again after the move.  What would be an acceptable z offset?

Also wanted to say your tuning guide has been great.  I'm new at all of this so it provides excellent tuning advice but also helps understand the concepts.

That is always the best way to go. If you get your bare quad flying perfectly - which these days is really very straight forward, then start adding stuff in.


If anything is not right you'll know exactly what it is. And then once you've got it perfect you can do it all again exactly, as many times as you like :)


The best builds I've done have started with the gps, telemetry, sonar and optical flow all removed and the mag disabled. Once it flies just as i want it then i enable the mag and start log checking, then when I'm happy plug in the gps and play with the position and shield. Only then the telemetry and final fiddling to make it all work just as i want it.


Then when i've done everything to my liking i take a load of photos for reference then i take it all off again, over tune the hell out of it and slap on the fpv gear and go for a super fast flyabout, but that's just me! 



Less than 150 is ok, but much lower is much better.


And thanks, it's badly flawed and outdated that guide, it was a practice run that i shouldn't have published and actually is slightly misleading in many ways, but it does encourage experimentation and understanding so for that I am still proud.


And yeah the concepts remain ok. I'm banking on a few days next week to update Gary with the new wiki pages.


My missus better cross her legs, I cant strap quads to table legs with a new baby in the house ;)

Arducopter drifts up when in loiter mode.

I've been enjoying flying the arducopter (APM 2.5 with FW 2.9.1) on my tricopter; however, lately I noticed that the arducopter has been doing something  I have never seen before.

When I put it in loiter mode in GPS lock, it now has a tendency to drift up and not lock in like it used to be. 

Has anyone experienced this before with their arducopter?

yes me!!! I have my quad setup with 2.9.1 , rctimer arduflyer 2.5 , baro covered, turnigy hal frame, 12x45 prop, motors hk 4006 530kv, default pids, stabilize works 100% ok, but im having trouble with loiter (it is slightly climbing)...sometimes after several seconds start drifting away, also now when i do yaw turns, it drifts away too..... never happened ... i will not start a mission with this issues... i was thinking to rollback to 2.8 , this regarding pids , motors, rctimer, baro or 2.9.1??? please help!



mi vibration range... very low i think

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Hello every one!!!

Yesterday I have received my PX4 kit with GPS. I Also tuned my Apm2.5 quad – removed almost all vibration. So I’m ready to be a beta tester of new 2.9.2 on both platforms.

Does anyone know when 2.9.2 as beta or RC? Is it will available on both platforms at same time? Or px4 version comes some time (what time?) later.

Thanks a lot for you work. 

Welcome to the club of drift away’s  while loitering, see here

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