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 need help getting the raw AccelZ graph. I have enabled Raw, then went flying. then went to terminal, then log browse. there are no files there. what am I doing wrong?

You need to download the logs to your PC first. Either use the log dump command, or use the log download tool.

Log browse, browses logs after you have downloaded them from the quad. 

I think next to browse is the download button.

It's quirky, complains about the com port, just keep trying, it'll eventually work. 

Bill, when I hit "log download" I get an "Error opening comport" every time. I've tried 20-30 times with no change. what am I doing wrong? it will show a logs window, but there's nothing in it. Does it make sense that when entering the terminal mode the connections shows as disconnected?

Mines the same. I just click on things until it works. Generally, the connect button in the upper right, then back to the terminal, and real quick before the terminal starts, hit the download button again. Sometimes I have to go back to the flight data screen and reconnect, then go to the terminal and real fast go to the download button. 

It's a real pain in the "A" and it's the one thing I've found that doesn't really work right in the MP. But once you get it, and know it does eventually work, then what ever subconscious process provides the magic, gets better at getting it to work. 

More specifically, this works every time for me:

Click "Disconnect" if you are connected, and ensure the correct com port is selected. Then click "Flight Planner", then "Terminal", wait for the prompt to indicate CLI is connected, then hit Log Browse or Download.

My solution to this problem is to click the terminal button. I wait for the terminal to start up. Then I look at the connect/disconnect button. If it is disconnected then I press the terminal button again. This generally restarts the terminal and changes the disconnect to connect.

To make the download work I generally need to ensure that the terminal has started with the mission planner saying it is connected.

Then i download my logs.

thanks guys,

hitting terminal again reconnects and I am downloading all my logs now. On to the next step :)

Hi Leonard,

I dont think the motor or ESC was faulty as it was only jumpy and jittery when I flew in alt_hold, but I think because of the jitters the motor or ESC got cooked because I could smell that lovely burned electronic smell when it crashed...


Nice! What motors/props are you running?

ok, so I've downloaded the logs and went to flight data/telemetry logs/tlog>kml or graph/get graph. I then select "zacc" under Raw IMU. I get a graph of Zacc_Raw_IMU_1 rather than AccelZ. I don't see sonar alt, baro alt etc.


any idea what I'm doing wrong?

Sorry, I can't reply below, so I'm messing up the thread by jumping back to the top. 

Anyways, fish around in all those numbers. Scroll down, a LOT. Look for rows marked RAW, and the AccelZ is in there. Highlight it and pick graph. 

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