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.


Views: 298129

Reply to This

Replies to This Discussion

Yes, it sure does!

Leonard, this time I was flying without the gimbal in order to prevent eventually fails during the tune or crash as this (fortunately) but others times I was flying with the gimbal working using stabilize mode only (firmware 2.8.1) and I haven't any problem. I don't know why it occurs (this time I was flying in Alt Hold) but I hope don't crash the octo another time. ;-)


P.D. My philosophy is "if you don't crash, is because you don't fly", congratulations for your work.

Why is it that with 2.9.x in the Mission Planner, the artificial horizon appears to lag behind or at least respond sluggish when I move/tilt the APM around? In 2.8.1 the horizon still responds very quickly.

Does anyone else experience this?

Thanks for the reasonable and open minded attitude Pablo!

The only way I can see Alt_Hold increasing the likelihood of a brownout is that it can be quiet aggressive on the throttle. But that shouldn't do squat on a 3s lipo using a BEC. So I don't have any other ideas or suggestions.

As always we will keep our eyes open for any trends of similar problems and generally keep this in mind when working on the code. But, if you make any progress on working out what happened or have some ideas let us know.

Thanks and good luck!

+1 on this.


Even with two tiny servo's powered from the APM my apm will brown out every time with just USB power, and occasionally on battery power if the servos are up to their limits (quad turned over for maintenance etc) I've never flown like this for obvious reasons.


I recommend to only connect the signal wires to the APM, then power the servos, as you say, from a seperate BEC.

I understand that 2.8.1 had a bug in it that was making it send updates faster than the user had set it to. This was corrected in 2.9.x so it now sends updates at the requested rate. Because the default rate is the same the update rate has dropped for 2.9.x.

That is what I understand anyway. Randy will correct me if I have got something back to front.

Randy, is it better to keep the default INS_MPU6K_FILTER value if it works ok?

20 is the best setting assuming everything is working ok.


     We removed some duplicate sends to the ground station between 2.8.1 and 2.9.1.  In fact, in 2.8.1 it was sending more than it was meant to.  You can adjust the rate that it sends to the ground station in the mission planner's Configuration, Planner area.

Does V2.9 support FrSky RSSI (PWM) input? I did not find any documentation on how to connect non-analog RSSI?


First real flights, without IMU6k_filter (still optimistic :) ). Here are logs, one for indoor test flight, the other was outside, windy 3-5m/s.

If there is something shoud be better, please, lets analyse! 



Been playing around some more and changed the apm mounting.

I have uploaded the last full dump log file, which had sonar on and sonar off although I don't know why it doesn't show it was disconnected when it was physically unplugged and the apm told not to use it on flight 2.

The quad is more stationary with the sonar off, fidgety but stayed relatively well put. When I put the sonar on again, it started to be more active on the throttle, probably the shrubs in my sloping garden, but causes spikes in the traces as it tries to maintain an altitude, is that normal?

So the question is have I sorted out the vibe issues or do I still need to look further in to it? No camera mounted on these tests.


Reply to Discussion



Season Two of the Trust Time Trial (T3) Contest 
A list of all T3 contests is here. The current round, the Vertical Horizontal one, is here

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service