APM Copter 2.9.1.b has been released to the Mission Planner and is also posted in the downloads area.
2.9.1b is a maintenance release incorporating changes to 4 default parameters that have been optimized since 2.9.1 was released.  There are also 4 minor bug fixes.  There are no code function changes or additional features.
The changes are:
1) reduce default INS_MPU6K_FILTER to 20hz
2) reduce InertialNav Z-axis time constant to 5 (was 7)
3) increased max InertialNav accel correction to 3 m/s (was 1m/s)
4) reduce yaw_rate P default to 0.20 (was 0.25)
5) bug fix for alt_hold being passed as int16_t to get_throttle_althold_with_slew which might have caused problems if you climbed over 320m.
6) bug fix for throttle after acro flip (was being kept at min throttle if pilot switched out of ACRO mode while inverted)
7) bug fix to acro trainer to do with roll correction 
8) prevent cli from being entered more than 20seconds after reboot.
Users are recommended to:
    Update Mission Planner to 1.2.41 and
    Update their flight code to 2.9.1b from the Firmware tab on Mission Planner. There is no need to go through a new configuration process in the Mission Planner.


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Hey - I finally helped find a real bug! :)

It was, to say the least, exciting. Sigh.

Hi Randy, sample question: where load rc-5 after rc-3, do I need to to Erase and/or Reset of APM?

Because after erase, I need to recalibrate ESC, motors, motorcomp, etc which are lost by erase.

Which are mandatory steps when load a new firmware/rc?


I tried again with rc5 and reduced roll/pitch (0,11) and yaw rates (0,15) and found it to be much smoother. ALT_HOLD and LOITER are really good. I also reduced WPNAV_SPEED to 400. The stopping is now smoother too. By reducing the THR_MID to 450 it reduced the drop in altitude on switching to LOITER from STABILIZE although still present. You know your parameters really well.

One thing I noticed is that RTL doesn't yaw in the direction of travel. It just stays at the last yaw angle while flying back. Any parameter to make it have yaw in the direction of the flight path?

Thank you,


My altitude is reading erroneously . I have my copter sitting on my dining table and it's reading over 300 ft. I'm not using a sonar. APM 2.5 is stock with case and foam covering the baro from 3DR.

Is there way to calibrate the altitude or barometer?


    Ok good news.  There's a new WP_YAW_BEHAVIOR parameter that you can set.  It defaults to 2 (look at next waypoint except for RTL).  This is one of those things that is definitely a personal preference 'cuz i've received requests to make it act in all these ways.

0 NONE - auto pilot will never control yaw during missions or rtl (except for DO_CONDITIONAL_YAW command received)

1 LOOK_AT_NEXT_WP - auto pilot will face next waypoint or home during rtl

2 (the default) LOOK_AT_NEXT_WP_EXCEPT_RTL - auto pilot will face next waypoint except when doing RTL at which time it will stay in it's last

3 LOOK_AHEAD - auto pilot will look ahead during missions and rtl (primarily meant for traditional helicotpers)

Is beta v3.0.0rc5 available to use?  I understand "at your own risk".  I'm wondering if it is a full functioning firmware available for anyone to try.


     Thanks as always for your testing.  Yes, we need to do something about dealing with bad GPS data.  It's come up from DaveC and a couple others as well.  It's possible it's more noticeable now that loiter is hopped up with inertial nav....or maybe it's better now that we have two sources of position (accels and GPS).

     The GPS failsafe is in the events.pde's "failsafe_gps_check" function.  It's called at 50hz and checks if we've lost GPS for at least 5 seconds.  We don't look at the hdop values at all....one idea is to reduce our reliance on the gps when the hdop value gets too high.  It needs some more investigation..


      Have you done the accelerometer calibration in the mission planner's Config, ArduCopter Level screen?


     Yes, it's available through the mission planner's Firmware screen.  At the bottom right you'll see a 'Beta firmware' link.  Click on that and you should see all the version numbers under the frame types increase to 3.0-rc5.

     If there are no objections from the testing team I hope to ask more people to start trying it soon after the Sparkfun AVC completes this weekend (I can't handle the support load of a new release until that's done).  Basically we want to take a slower approach to the release than we did with 2.9.  So we're doing extensive testing with the beta testers, next we will ask a wide audience of people to voluntarily give it a try.  After that group is all happy and we've sorted out any issues we will move 3.0 to be the default.

Hey Randy,

Thank you for replying to my inquiry.

I just attempted the accelerometer calibration in the missioner planner's config, but the altitude is still reading over 300 ft while sitting stationary on my dining table.

Thanks Randy.  The reason I asked is I installed 3.0 on my quad and can't get the motors to come alive.  The ESC's are calibrated and all four function correctly when connected individually directly to the Rx throttle.  The APM arms but the ESC's just beep as if throttle is high on power-up.  I did Tx calibration with throttle trim and sub trim at 0.  When powering the quad I even had the Tx throttle trim set to lowest position and still ESC's won't behave.  Maybe I'm missing something?

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