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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Test with ArduCopter 2.9.1. Was in Loiter and switched to Land. There was some jerkiness in loiter but it is pretty good even with my non-updated MediaTek GPS (the update process looks a bit daunting and I'm working on getting my uBlox replaced...never worked for some reason). Altitude hold is awesome especially with the modification of the THR_MID parameter since you don't get the jumps/sinks when switching in and out of ALT.

I have the 880 motors with 11 inch props installed. The video flips around in the end because I was worried that I would hit the pole but it cleared it. This release is looking really good and can't wait to try it with the uBlox. Thanks!

If I intend to remain with ArduCopter 2.8.1, which Mission Planner should I use? I did upgrade MP to latest 1.2.32 and it looks the accelerometers are not more calibrating, HUD remain tilted and is not put is back horizontally.

I did notice on MP1.2.32, calibration page, is it mentioned "2.9+" under the calibration button. Do this means MP1.2.32 is only for 2.9+, correct?

I am also curious as to what version of Mission Planner supports 2.8.1 and at what point is it no longer supported (2.9.+ )

Does anyone know the answer to this as it is quite important to what version of ArduCopter firmware you are running.

Thank you for looking at it.

I'm using the ESC from the DIYDrones Hexcopter kit with the defaults, so it looks like the defaults are Soft Cut-Off Low Voltage Protection, with Medium Low Voltage Protection Threshold, 2.85V per cell, 11.4V for 4 cells. Regardless, I would think if the ESCs hit their cut-off voltage, the APM would continue to work and send telemetry. BTW, I'm using the APM Power Module with Deans Connectors.

I'll see if I can replicate it once I get it back together, albit a little closer to the ground.  :)

Having trouble uploading 2.9.1

Try reboot the computer if you haven't already?

Randy,sorry to be a pain in the but,am I right in saying if I purchase a PX4,it will run 2.9.2 when released and use mission planner,your's gratefully,Marty.and thank's for your help

Good point.

So now we need an adaptive system that correlates Thr_Cruise to a motor battery voltage! :D

Hi Randy, uploading a video clip, to demonstrate the problem;

I now have many auto missions with my new H frame quad and 2.9.1 is fantastic but I have been experimenting with the more exotic mission planner waypoint functions.

It probably me but the only ones that seem to work as advertised are waypoint, do change speed, loiter time and land.

I was hoping ‘loiter turns’ would circle nose to center to enable filming of a selected point. For that matter circle mode doesn’t seem to work either, more like a drunken loiter. Have tried different radiuses but it seems to manage about ¼ turn and get stuck.

I need the quad to reach a certain height to clear treetops before proceeding but ‘condition change alt’ seemed to get ignored.

Like I said it probably me but any advice appreciated.

Quick video of simple mission at only 2m/s



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