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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No problem Jeff,

ACRO_P of 4.5 to 9 (202.5 deg/s to 405 deg/s)
ACRO_TRAINER,1 (0 if you want to do flips but you can't do loops yet)

Let me know how it goes!

I am not a beginner. I am used to fly helis from 100 to 600 size. Quad is so relaxing, so stable. I can tell you Acro mode with 0 setting would be very hard to a beginner to start in this mode. You guys did a nice job allowing those kind of configuration. People should read about the updates from this new firmware instead whine about it. I can tell. I have 3 boards here and I am using 2.7, 2.8 and the new 2.9. 2.9 is far better. Just flew my 2.7 and I dont like it anymore.   Cheerz!

This is because you have switched to loiter (Alt Hold) while you are going up. Because you are increasing altitude when AltHold is switched in you get an error build up. Alt hold is quiet aggressive at correcting altitude errors and quickly drops the motors to bring the copter back to the desired altitude. The motors aren't completely stopped but it does sound like it.

Exactly. This is how I avoid this issue. I let the Quad hover in acro just under mid stick. I start to drop VERY slow and kick on Loiter/ALT_HOLD. Cannot even hear the transition. 750KV on large 4S. 2.9 is far superior to 2.8. I have done Autolands in the tightest spaces, hands off, transmitter down, motors stop. On 2.8 this was not pretty.

I am glad you are enjoying it. We still have some improvements to come!

Stock settings on the loiter.  

As I mentioned, I've tried using both P and I terms to eliminate the behavior, but didn't get it to work.

Setup is a fairly stout quad.  Aluminum arms, G10 fiberglass center plates.  DT-750 motors that have been rewound for about 880kv and 10x4.7 props.  The stock tune seems to be pretty close.  I've increased acro_P gain to 0.155 acro_I is at 0.14, and acro-D at 0.005.  All other settings are as stock.  Hover is at about 45% of stick.  It's a bit heavier than I'd like, I need to put it on a diet.

Alt hold is amazing compared to 2.8.1, loiter from a hover is awesome...I just love flying the thing...but when I loiter from speed it takes a long time to stabilize to a point.  It's nerve wracking to see...I'll try to get some video if I can.

I've noticed the same on my quad...I thought it was the motor stopping momentarily, but figured it out when I walked over to it and tried to lift it from a hover...the slightest lift resulted in almost zero throttle (I think 13% is the default minimum?).  then I pushed on it to try to send it to the ground...that was fun.  It resisted strongly!  I recommend it to all to try...but be careful!

After I figured out it wasn't a problem it was fun to abuse it!

Thanks for understanding.  I hope I didn't come across as complaining too just took me by surprise.

I did read the release notes, but I just overlooked this one.  It's still confusing to me when I read it, but with a new understanding, I can see how it documents the change.

You guys are doing good work.  The firmware and software have improved dramatically since the first time I tried to use this board...after hours and hours of tuning I got disgusted and put the board aside and went back to my trusty KK board.  I had some time over Christmas and thought, I'll try this again...tuning happened fast!  The difference was night and day.

I'm pby not a good enough pilot to give you the feedback you'd like on the full acro mode, but I can say, it's a dramatic improvement from the first time I tried it.  I'd do what I can to give you feedback though.

I have noticed though, that I tend toward liking a more aggressive tune...


     In the original 2.9 release video from DaveC he pushed it down with his hand to demonstrate how quickly and strongly it resists.  We asked him to swap that scene out for the bit where he pushes it with a broom 'cuz it's definitely dangerous!

For most of the people who have tried auto-land and usually do it, does the default descend rate of 50cm/sec work fine? Or you need to reduce it? I want my quad to touchdown very lightly and smoothly as I fly on tarmac. What is the ideal rate that the experts suggest?

Help Team, Ok My 1st log or my Z data, I have my APM 2.5 mounted to triple layer of double sided sticker rubber its one solid piece, my frame is a DJI 450 spinning 980kv SSky's, this was logged while Im still tweaking my PID's in gusty windy weather

Do I have too much vibes going on?

I use 30 cm/s. gives it more time, especially in wind to find its mark

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