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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Congrats gentlemen. Really excellent work.

I can build and upload 2.9-rc5 no problem. However, when I then try to load the released 2.9 via mission planner, the radio calibration does not work in that it will not refresh values from the transmitter. Going back to the rc5 build works fine again. I have tried various permutations of erasing and resetting from the CLI but no luck. Is there something here I am missing?

Great Video, great 2.9, :-)))

lots of thanks to all who made this happen!!!

Let’s go flying, can’t, mad Southerly blowing :-(

Thanks for the new version, will test it just as soon as the snow passes...

got a couple question:

is this release is the same with RC5 ?

with this accel graph, i should keep my INS_MPU6K_FILTER to 0 right ?

fly tested with my tri, stock pids, except for rate_roll.. alt-hold was very nice.

i personally like to land with alt-hold, just lower the throttle and it will gently descend. once it hit the ground, close the throttle and switch back to stabilize..

any idea how to tune throttle accel P and I ? if is it too high or low ?

KUDOS TO THE WHOLE TEAM...specially to Randy and Marco...

Accelerometer calibration needs to be done everytime or just once???
I had the same problem but not exactly the same though....

Go to the advanved parameter list and choose 0 for voltage and 1 for current...
I have my voltage plugged into A0 and current into A1.

Probably the numbers need to be changed in the battery monitor menu

Thanks! Just once.

Thank you for the reply Saurabh Srivastava I tried A0 & A1 but it gives me 050Saurabh Srivastava instead of 11V .With the 3DR power module and his cable I dont know what pin are used ,but A13 is correct for voltage (gives the right value at least)

Stefano: I may have missed something but I didn't know the CLI could be used over wireless. Has that been added while I wasn't paying attention? (very possible ;-))

dudz: you've probably got a problem with your sonar sensor. Disable it and try again. 

Yes Chris, now is possible, but also with the release 2.8... :-)
There's some good security for skip the CLI via wireless if the motors are armed or the quad is in flight.
You can enter the CLI via radio only in the first 20 seconds when you connect the main LiPo.

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