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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Yes, they were still physically connected. I did test in Terminal to see if indeed they were disabled. But indeed still electrically connected.

Wow, if I can get mine to loiter that solid I would be one really happy camper.

As you said, maybe some of us have vibration problems that hadn't effected problems before now.  I would appreciate a tutorial of how to look at my raw accelerometer output in the log files.

Maybe that should be step one before upgrading to 2.9?

An easier to get gel vibration damper is Moon Gel.  I found it at my local music store for about $7.

The step one before upgrading imh is "remove unwanted vibration" from your quad, then upgrade to 2.9 and play with "INS_MPU6K_FILTER".


Select the terminal tab. Reset the APM (or power cycle). Press enter 3 times.

You should now have the CLI screen,



Had the samme issue,

Uninstall the APM, Manual remove the remaning files in APM Planner folder under Program Files (but save the log folder if you have log files you want to keep).

Install 1.2.32 from here

Removing the files from the APM Planner folder might not be required, but had a lot of files there.


I'm seeing something odd with 2.9 that I never noticed with 2.8.1 on my APM 2.5.  My copter is sitting dead still on a table and I'm seeing the altitude (and groundspeed a litte) drifting both up and down.  It starts out right around 0 on boot, moves a little, then settles at 0 for a bit, then it starts to drift.  I've tested it with and without the Ubox GPS attached and I get the same results.  Is this normal and I just never noticed it with 2.8.1?  See attached screenshot....


I found the same here and Marco replied.


I'm not sure if it's the same problem although it might be.  The AH attitude isn't bouncing around like in your video.  It's staying dead still.  Just my altitude is drifting either predominantly up or (after a reboot) predominantly down.  AS and GS is bouncing between 0.00, 0.02, and I see it up as high as 012.  Distance traveled is slowly going up as well.  I just tried setting the AHRS_GPS to 0 and at first I thought it was better because it started off at 2 feet (about the height of the table).  But 7 minutes later it's now at 9.50 feet and steadily climbing.  Distance traveled has gone from 110 feet to 275 feet since the boot as well.  I did the calibration.  Not sure what the deal is but it seems like that would cause problems in flight?  Just since I've written those couple of sentences it's now at 11.5 feet of altitude. 


     The barometer drifts around a bit so 10 feet (about 3meters) could be just that.  ..but if it gets to 110 feet (30m) then there's definitely a problem.  You could also try arming the motor (even with batteries disconnected) and you should see it streak back to zero but then start to drift around a bit more but again only within a few meters.

     If you want I can check your dataflash logs for you.  Please enable the INAV message and also during the test arm your motors (with lipo battery disconnected for sure!) and leave your throttle above zero for a while (the dataflash only records logs when the motors are armed for the most part).


     You can sort that out with save trim or auto trim.  The wiki page has been updated now.   Another very direct way to fix it is to directly change the AHRS_TRIM_X and AHRS_TRIM_Y parameters.  X is for roll, Y is for pitch and it's in radians (1 degree = 0.017453 radians).  So say your HUD was leaned over at 10 could change the AHRS_TRIM_X to 0.174 (or maybe -0.174) on the MP's Adv Parameter List screen, press Write Params and it should come back to level.

     Enough people have complained about this that I'll sort something out for 2.9.1 where as part of the accelerometer calibration it puts an initial value into the trim so that the HUD comes out flat.

Yeah, it looks like it's just baro drift and I never noticed it before.  I reloaded 2.8.1 and watched it behave similarly.  Like you said, when I arm it streaks back to 0.


So are the calibration settings saved when you bounce between versions?  I will probably redo the the accel calibration regardless, but I was just wondering.

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