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'm a little worried about that solution because using the level command is removing all the accelerometer scaling and offsets.  I think it will negatively impact your alt hold performance significantly so I higly recommend using the new accelerometer scaling method and then using the auto trim to sort out the misaligned hub.  You can even do the "save trim" method without flying..just push your roll or pitch stick and click the channel 7.


     Great, thanks for that.  Hopefully we can get this sorted.


    great pic!  No need to recalibrate accel and compass if you save the params.

Finaly I solve my configuration problem for the 3DR power module , The sensor pins are A12 for current and A13 for voltage .In mission planner I édit ParameterMetaData.xm to change the values from

      <DisplayName>Battery Current sensing pin</DisplayName>
      <Description>Setting this to 0 ~ 13 will enable battery current sensing on pins A0 ~ A13.</Description>
      <Values>-1:Disabled, 1:A1, 2:A2, 13:A13</Values>


<Values>-1:Disabled, 1:A1, 2:A2, 12:A12</Values>

Then I can put the value A12 in BATT_CURR_PIN and I have correct amp values now

Anyway my hexa flyes well in 2.9 !! nice work guys !!

I am still trying to find out if and how the Loiter jerkiness (as I call it) can be prevented, the 3S to 4S change would probably need the normal PID's reduced as I'm not sure yet what parameters to change to stop the jerkiness in Loiter. Let us know if you experiment?


I hope this is ok to post this here, at least I figure the correct people will see it.  I had been seeing a small problem with the MP update.

I had updated to ver 1.2.30 when it first came out, since then (I think from the day or 2 after it updated) I have been getting the update message the first time I run MP every day, I hit ok to upgrade. It starts and gets through quite a bit of updating then gives me a message saying update failed (message about files altered, and one time about part not being a valid app, or slightly different messages). this happened to me quite a few days, when finished it still says ver 1.2.30 so I check the downloads page and see 1.2.30 s the latest version posted. so I let it go till today.

Today I uninstalled ver 1.2.30, reinstalled it, ran it and got the same results, update message, I hit update and failed. I re downloaded ver 1.2.30 and tried again, same thing.

finally I uninstalled and reinstalled ver MissionPlanner64-1.2.19.msi, got the update message, ran it and it worked, now I am running ver 1.2.32. (I dont see it in the downloads area, but it did update to this.

Just thought I should report this, incase anyone else is seeing the same thing..



I have exactly the same issue. The artificial horizon after calibrating the accelerometer a couple of times is still leaning to one side. Only by a couple of degrees, but as far as I am aware the calibration platform is flat. Will a couple of degrees make a difference or should the horizontal line be perfectly flat after calibration.

This is on a Hex.

This's Loiter and Guided mode by 2.9 

Hi Randy,

So am I correct in saying that one could calibrate the APM board (with casing) before it is build into the quad? I'm thinking about connecting the board and running the leveling sequence while resting the case on a table in various postions and then keeping the INS_xxx and INS_ACCSCAL_xxx values.


Nice Pic

Graham: What GPS are you using? I'm seeing totally rock solid Loiter with the uBlox. No jerkyness at all. 

Don: I think what's tripping you up is that the throttle must be in the middle position to hold alt. (There's a "deadband" of 20% or so in the middle that all counts as middle). Remember that in this mode your throttle now is controlling altitude, not the throttle itself.

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