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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Liking the sound of ESC calibration for SimonK.

Hello..does this means we can use new type of ESC wich have FET instead of diode?The name is UltraESC

they are described as this;

"new ESC based on a MCU which has a HW PWM unit especially for driving three phasis BL motors.
because of that it can do high frequencys (6-128kHz), a clean active freewheeling(HW deadtime generator and complementary PWM) and the mcu dosent need to hadle the PWM .. so there is more time for other tasks"

here is link to RCGroups 

in one of the videos from Warthox testing them at the end it says:ultraESC setup;imput PWM 1KHz,motor PWM 32KHz,active freewheeling enabled(shyncronius rectifications),MWC(multiwiicontroler) output PWM 1KHz

...since i am no expert at all i wonder is that kind of setting is possible ("with the 11 or 16 bit timer of the atmega32u4 and the atmega2560 its no big deal  its just a different timer adjustment. the 1kHz signal is also the same as MWC's normal signal .. just 500-1000us instead of 1000-2000us. i just did some test versions. if the ESC is available and the MWC community is ok with it, ill add a define 

it should also work for the 328P's 8 bit timer .. but i dont tested it for now (it would be a waste of resolution  )."....with APM2/2.5 and where

I wonder what its made off, looks like carbon. I guess any conductor will do.


That GPS signal display in the link is good. Does anyone know a way to show our APM GPS in a better way. Number of sats and hdop is not that informative.


I suspect many people fly like me, with a PC nearby indoors logging, but not visible or audible. I turn my PC speakers way up and open the windows just to keep track of mode changes and battery levels.

Does anyone know of a simple device to get PC audio into an earpiece ideally up to 300mts? I guess like a walkie talkie.

If that were possible, more use could be made of MP speech warnings, adding things like GPS warnings. There should also be a reasonableness check for if the APM is naving to anything over 500mts away.

A bluetooth headset/ear piece would do the job, assuming your computer has bluetooth.

I set my Radio for maximum range and resolution. Personally I have never set my throttle fail-safe. I set my channel 7 to RTL and my receiver fail-safe to 1/4 throttle and channel 7 high. This means if I loose radio contact I get RTL but I can always manually switch into RTL at the flick of my channel 7 switch.

This isn't what I suggest others do, it is just what works for me.

Just while I am on the subject of RTL, this isn't a mode for the first time flyers. You need to get stabilize running and PID's tuned. Then you can ensure that your navigation PIDs are tuned and working well. Only then can you safely use RTL.

My normal take off procedure is to turn on my Tx, then power my quad. I then give everything a quick once over, reset my flight timer on my radio and check for a GPS lock. I do a careful launch in stabilize and after about 10 seconds I land at my desired home position. I disarm and rearm and launch again. I then increase altitude to 5 meters and engage Alt_Hold, then Loiter being ready to switch back to Stabilize if there is a problem (GPS can be moody). Only after this will I rely on RTL to do what I expect. Then I can FPV.

As for the last part of your post, I am not sure I understand what you did to get higher than your min_throttle setting when your motors first start turning. My understanding of the code suggests that you will always start at MIN_Throttle setting as you increase your throttle, otherwise you would never be able to arm.


     Not sure this is too related to 2.9 really.  But in any case, it is likely possible to support ultrapwm but you'd need to make some changes to the APM_RC library.


That is probably the only thing I haven't previously filmed!

Going from memory, set throttle trim midway, calibrate tx in MP.

The idea then was to be able to set trim to minimum to give some throttle dead space. What happened was that you could increase the throttle stick, nothing happens, then suddenly  at about 1/4 stick, you get sudden 1/3 throttle or so.

Before and since then I have always done the calibration in MP with throttle trim at min. Difficult to get that wrong accidentally... And flown with trim at minimum.

Never had a problem, many, many, auto flights, but just wondered where others place their throttle trim (a) at calibration and (b) during flying?

The point I make is that if you accidentally move the trim post calibration, then funny unexpected things can happen in flying...

I've been flying all my quads with SimonK FW for the past18 months, never had an issue...

In fact I wouldn't build a quad now without incorporating ESC's not flashed...

Randy,  after I load RC2, can I reoad my parameters I tuned for RC1, or do I need to set to default and change manually..  Usually when I reload, I do a wipe........thanks Jeff

Hi Jeff, You should be able to reload your RC1 parameters. I don't believe that it will be a problem. In general though I would wipe.

Leonard. Thanks. So you suggest to erase logs and EEPROM and reset before I install any revision. That's what I do but my quads are overpowered DJI 450 so I change about 12 parameters manually. Thanks! JEFF

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