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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Try setting the LED MODE to 99. If the flashing is much faster when it occurs, you know that it's the low battery alarm that's occurring. 

Yes, it's IMO kind of annoying that the Arm remote LED behaves as a regular "copter LED" as far as low battery etc. flashing (actually, all except the GPS 3D Lock remote LED will, IIRC - been a while). I'm afraid you won't be able to prevent that without changing the LED code, which isn't difficult, but it puts you on a road you might not want to get started on.

I don't think its low voltage.  I'm running two 2200 3S LiPo's in parallel and when I recharge they each fill with ~ 950 mA for a six minute flight.


I am having a problem with land mode with one of my copters, I have 2 quads with apm25's on them. When I switch to land mode I pull the throttle to zero once I see it is bringing itself down, on one copter lands perfectly the other lands perfectly sometimes, at other times when I switch to land mode it brings itself down nicely and touches down, but then it raises its self about 1/2 to 1 foot then drops then repeats, like it bounces. I have t switch to stabilize mode, with the throttle at zero,  to get it to stop I am not sure what is causing this. I know this copter has landed fine in the past (well it still does at times)

 I have checked through all connections, and reflashed it, erased the parameters, I think I did everything I can think of. I will attach a log file that has a good landing on it and a bounce landing on it,  . If someone can take a look at it and let me know what they think it would be greatly appreciated.



edit: I forgot to attach the log, I will below

file fro above post, bounce landings


Don't be distracted by that fact (I was...), it doesn't matter, the remote Armed LED will eventually flash. I never did try to figure out exactly why they do the "low voltage flash" when I appear to have set the low voltage level properly and the battery is nowhere near discharged. My point (for me at least...) is that I never want the Armed LED to flash unless the APM is disarmed. How about you?

I don't care if the other remote LEDs flash (I have one for GPS Lock and another for good/low HDOP) once the copter is armed (under any circumstance) because they aren't going to be potentially dangerous, and they're of no real use to me once the copter has lifted off anyway. I just don't like my copter sitting on the ground, just after a flight and not disarmed, ready to go for maybe another short flight, with the remote red Armed LED flashing such that it could be interpreted as disarmed. Naturally I always did a "disarm" until I fixed it, but still... I have an external lipo monitor device that appears to be very accurate and it's set similar to the APM low-voltage, yet the external device doesn't beep; I go by that device since I tested it and it works properly.

Sorry for the long reply, but we all have different requirements, and the beauty of our OS code is we can change it to how we like when it doesn't match the general requirement as provided by the developers.

Its probably not the same problem, but I have bouncy landings when I have mounted the APM on very soft mounts.

For now I only have the two remote LED's.  It only makes sense that the ARMED LED stay lit when it is ARMED and go dark when NOT ARMED.  Blinking at altitude doesn't make sense at all.


I actually removed the foam from under the apm to see if it would help.  I am not sure if it would have ever landed because I always switch to stabilize to shut down, but it seems like it gets a little higher each bounce, it flys back up.



Increse your landing speed. The higher the landing speed, the earlier the motors will cutoff, and less bouncing. The key is to find a sweetspot between acceptable landing speed and motor cutoff bouncing effect.

Post Blog Rejected: RC Helicopter Kills Toddler in Malaysia

Hi John,

It is the mission of DIY Drones to only promote the positive side of hobby drones so, unfortunately, your blog post will not be approved. This unfortunate incident has already received sufficient exposure on other web sites.



Thomas sorry but I think you miss the point here. Firstly this happened yesterday about 30min drive from where I live so how can it be so fast it is now everywhere else on the other web sites? Stuff that happens in Malaysia just doesn't travel out that fast mate!

Its nice to post the positive side of DIY RC models but people also need to be made aware of the possible dangers of them as well. May be if you post this on DIY Drones it could help prevent a similar type of incident which was the reason I posted it.

Now how are you going to feel if someone else child get killed and it might have been avoided if you when and posted this article?


I use v2.9.1-dev, make level und do Radio calibration. All OK.

Now I turn on under Hardware Optflow and sonar, then set CH7 to sonar.
Disconnect vom MP

Try to connect und now I get no Mavlink connection.
Can anyone understand?

Regards Peter

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