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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My GPS problems are solved.  The Spektrum TM1000 telemetry was interfering so it has been removed.  I also had it mounted too close proximity to the GPS.  The GPS is now mounted on top of a 3/8” diameter carbon fiber rod and is positioned high above the APM.  The 900 MHz telemetry is mounted on the opposite side of the Quad form the GPS down low on the landing skid.  I use a ¼ wave antenna made from stranded wire instead of the rigid plastic antenna furnished with the unit – better for crash I think.  The GPS now allows a solid Loiter as soon as I lift off after short waiting period for the GPS LED to show a 3D lock.    I woke up at 4AM this morning and thought it would be a good idea to fly the Quad - 60 YO man flying his toy in the middle of the night.  I’m having a blast with this thing.

If i can suggest that genius guy who make new web page change the WRONG picture of Y6 setup

and make the right one as here

this stupidity cost me 3 carbon props and one 60$ motor(wires from base of stator pulled out),bent leg too...


     Sorry for your troubles but thanks for the report.  It'll be fixed shortly!

eh,it was my foult too,bcs i was so sure everything is tuned well that i try to take off despute visible problems in control....i went y6 way bcs i wanted redundancy as well as camera view clerance,but i must say that y6 is most dificoult setup i had so far,its wild beast hard tu tune and everything must be very precise in 1/10 of mm.....also i have to report that new Ublox 7N module ( APM2 works very well,but i am not sure if used all the adventages of it


I think in addition to removing the TM1000, raising the GPS well above the spinning carbon props is the answer to a solid lock.  Now I can lift the machine immediately when the GPS shows a lock and put it into a stationary Loiter without it veering off in some direction like a headless horseman.  It doesn’t need extra time to acquire the satellite constellation or almanac.  Now I begin the next phase of fine tuning the flight parameters, investigating alt hold, and finally autonomous missions.  I think I’m about half way to the finish line.

Thanks, I will give it a try, though, I am not sure if I described it correctly. My one copter that lands good, it bounces a little but this one, it lands then it seems the motor speed increases to fly it back up.

I will give t a try anyway, I am wondering if I am not trying to land too close to the ground, I have been testing it from only about a foot high, maybe I should try higher starting point.


"ArduCoper V2.9.1" code on "VR Brain" FC board by "Virtual Robotix Italia" (MTK GPS):

Special thanks to:

- Roberto Navoni and Emile Castelnuovo (by "Virtual Robotix Italia")
- 3DRobotics
- ArduCopter Developer Team
- DIY Drones community
- Lorenzo Gualiumi (the filmer)

Soon I'll start also same tests on PX4...


Nice copter! And the PH is not bad for MTK anyway :) . I will do my next vaction in Italy that's for sure now :)

How about a photo?

Hi Marco , 

thanks for your great review :) Today and Yesterday the Pilot of VRI doing his first Hacking Day. We solve a lot of problem on our quad and the result after setup is wonderfullllllll :)

Great stable flight

Great loiter with Ublox GPS 

Great altitude hold and auto landing .

Great return to landing point and

Great Auto Navigation 

After solved the bug on 3dr radio also the telemetry was very usefull for debug the problem to our quad.

These are the VRI (Virtual Robotix Italia) pilot during hacking day at the field ,with their quad with onboard VR BRAIN 4.0 and 3DR Ublox GPS :)


This is our fb page :)

with realtime update of our work :)




Well,  I don't think that's it, I tried increasing the landing speed to just 60, first try it landed beautifully, like it has in the past at times. The second, third and 4th try, not so good. other than that it flys great in stabilize, althold, and loiter modes.

I t actually goes up about 2 or 3 feet on the first  re-lift, when coming down after re-lift, my front props hit the dirt on a couple trys and my back right (#4) hit dirt on the last try. ( i think that is because I switch to stabilize mode at zero throttle to get it to stop) I dont think t is a param because when it works it lands so nicely.

 The only thing I have done lately was to recalibrate my esc's and I am using a different transmitter. I was using a 9x and changed to my futaba 9c because one of the gimbal pots went bad on the 9x.

I also disabled the sonar and optical flow sensors, in case they were causing problems

here are the logs from today



     Someone has fixed it now!. txs again.

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