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 had a good experience flying 2.9 today after being away for 6 months with no copter. Had my first ever rock solid loiter with a bit of wind. Props to the developers!

I rebuilt my original 3DR quad with a jakub gimbal using good servos, and put some dt750s with gemfan 11x4.7's on, and a set of 3DR radios. It goes pretty well now!

The only thing that is annoying me isn't really 2.9 specific, but it's that my minimOSD won't update with data until I connect to mission planner with the 3DR radios. I understand this is because the tx line isn't connected on it, but a lot of the time I will go out and fly without taking a laptop, and I still need the OSD to work (mainly for battery info etc). I've tried enabling the SR3 update options in the parameter list, but it still doesn't update the OSD data without the radio being connected. (thread link)

Is this the best way to achieve operation of the OSD without radios being connected?

Will it actually cause problems if I do connect the tx line of the minimOSD in parallel with the 3DR radio? 

Thank you for the help, I'll try this tonight.

Kind regards


If you have only the minimOSD connected then you will need to add the OSD Tx lead like so:
UART           OSD (osd only)

could also connect

I just checked the ArduCopter wiki and nothing has been posted there in terms of updates. It does not mention that 2.9 is out. I am assuming that all the tips that are there will no longer be valid as far as initial setup is concerned? They seem to apply to 2.8 but with all this new calibration stuff, I am not too sure what to do.

I am about to mount my APM2.5 with Ublox on a spider X quad but a little reluctant to try and fly it. With all this new information out, I suppose I should wait until the wiki is updated? Is it safe to apply 2.8 setup routine to the 2.9 software at all? Just trying to avoid seeing my quad jet into the sky full speed like a bat out of hell!

2.9 release looks promising, amazing work from the dev team, you guys are incredible. I can`t wait to try, just being a little chicken here with all the mixed feedback.

Wiki is traditionally always out of date, but a good general guide!

v2.7 series was pretty solid on default config.

V2.9 has the usual teething problems, but don't ignore the setting up procedures as shown at the beginning of this thread, which over rides the wiki.

Hi Guys,

Please help me out. I have uploaded 2.9 to my Quad (previously on 2.8) and have made the changes as described on the first page of this thread.
Problem is this, I could hardly hold the quad at a fixed altitude after the changes due to the throttle being very un-responsive I then changed the Throttle rate settings back to what they where in 2.8 and that worked allot better. Why? (this is taking the throttle rate P from 6.0000 to 0.6000)
Also, when I had my copter connected to the Mission planner to download logs just now, it talked to me. It said something like BAWI every 10 seconds or so. Any idea what that could be?
Thank you

Ok.. just have a quick question...

What is the parameter "AHRS_COMPASS_USE" used for?

When I upgraded to 2.9, it got enabled and my quad used to yaw about 25-30 deg automatically in the stabilized mode. I was so damn worried... when I disabled it, everything worked fine... does that need to be enabled? Would disabling have any other impact on the quad?

Also, when I start the quad, the stabilize mode with "simple" works normal... but after a few minutes of flying, the compass seems to be disoriented from the original heading....
If I'm overpowered, would it help to curve throttle so hover is near 50% mark instead of 30%?
Another question. ..

I have leds connected to my APM. Once the gyros are initialized, they start blinking. Once I arm the quad, the frequency of blinking increases... earlier in 2.8.1 they used to go solid. However, in 2.9, at times they go solid and sometimes they blink fast.

My led use is set to 1. What does the blinking mean?

Randy, I have just flown again after upgrading my onboard Mediatek GPS to v1.9. Loiter is still quite busy/twitchy/jerky but I can't objectively say it's better than v1.6 in this respect, positional hold seems good but again I can't say without a doubt it's better. Is there a way to quantify the improvement from the logs?

Looking forward to the new Loiter

Initially, I saw the same thing. I have mine set to 99. Green LED's on the front arms flash on boot and then go solid on a GPS lock and flash 3 times when a waypoint is hit. The back legs have red LED's and they flash on initial boot and go solid when the quad is armed. When I first set it up the red ones would flash rapidly when the quad was armed. They are also set to flash 3 times upon hitting a waypoint. (so far the waypoint flashing is untested) However once I powered down and then back up again, everything seemed to work just fine, without the fast flashing upon arming. I don't think that I changed a thing - but there's a lot going on during a complete setup so it's possible that I may have tweaked something and not known it. (this is on APM 2)

WOW!  that is a super stable release!  Will try to do a video tomorrow, winds were so strong this weekend that I did not think it would fly.  But it did.  Great job guys, this is worth sending a newsletter email to all my customers telling them to make sure to update to 2.9 era! 

Super excited, now let's get the Follow me box working! :) 


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