Warning #1: an issue has been found with Tower's Pause button which can cause the vehicle to fly to an old position if the vehicle has not sent a position update to Tower in some time.

Warning #2: Copter-3.3.2 fixes a bug found in Copter-3.3.1's desired climb rate initialisation which could lead to a sudden momentary drop when switching from Stabilize or Acro to AltHold, Loiter or PosHold.

Warning #3: Copter-3.3.2 fixes an issue found in Copter-3.3.1 which could lead to hard landings in RTL or AUTO if the WPNAV_SPEED_DN was set too high (i.e. >400 or 4m/s) and/or the WPNAV_ACCEL_Z was set too low (i.e. <100 or 1m/s/s).

Warning #4: a bug was found in Copter-3.3 which could cause a sudden crash if you abort a Take-off initiated from a ground station.  Video description is here.  The bug is fixed in Copter-3.3.1 so we recommend upgrading.

Note #1: AC3.3-rc8 corrected a long standing bug in the HDOP reporting.  HDOP values will appear about 40% lower than previously but this does not actually mean the GPS position is better than before.
Note #2: if upgrading from AC3.2.1 the vehicle's accelerometer calibration needs to be done again.
Note #3: set SERIAL2_PROTOCOL to "3" and reboot the board to enable FrSky telemetry like in previous versions.
Note #4: the wiki will be updated over the next few weeks to explain how to use the new features

Copter-3.3.1 is available through the mission planner.  The full list of changes vs AC3.2.1 can be see in the ReleaseNotes and below are the most recent changes since AC3.3.

Sadly this version (and all future versions) will not run on the APM2.x boards due to CPU speed, flash and RAM restrictions.

Changes from 3.3:

1) Bug fix to prevent potential crash if Follow-Me is used after an aborted takeoff

2) compiler upgraded to 4.9.3 (runs slightly faster than 4.7.2 which was used previously)

Changes from 3.3-rc11:

1) EKF recovers from pre-arm "Compass variance" failure if compasses are consistent

Changes from 3.3-rc10:

1) PreArm "Need 3D Fix" message replaced with detailed reason from EKF

Changes from 3.3-rc9
1) EKF improvements:
    a) simpler optical flow takeoff check
2) Bug Fixes/Minor enhancements:
    a) fix INS3_USE parameter eeprom location
    b) fix SToRM32 serial protocol driver to work with recent versions
    c) increase motor pwm->thrust conversion (aka MOT_THST_EXPO) to 0.65 (was 0.50)
    d) Firmware version sent to GCS in AUTOPILOT_VERSION message
3) Safety:
    a) pre-arm check of compass variance if arming in Loiter, PosHold, Guided
    b) always check GPS before arming in Loiter (previously could be disabled if ARMING_CHECK=0)
    c) sanity check locations received from GCS for follow-me, do-set-home, do-set-ROI
    d) fix optical flow failsafe (was not always triggering LAND when optical flow failed)
    e) failsafe RTL vs LAND decision based on hardcoded 5m from home check (previously used WPNAV_RADIUS parameter)

Thanks for your testing!

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Perhaps it's usefull if you share a photo of your build, It's looks strange that you have so higher values in Roll than Pitch, did you complete well Pitch and yaw autotune?

It's usefull for experts if you share your autotune log too. 


    yes, you got lucky there.  That's the exact case where it gets itself into a bad state.


    ok, sorry for the troubles!

To add a bit more detail, internally Copter has an auto-armed flag that should always be true if the vehicle is flying autonomously.  It's primary function is to stop the vehicle from beginning an autonomous mission unless the user has raised the throttle.  In the case of the take-off being initiated from the ground station we were not checking that flag.

Copter-3-3.1-rc1 has appeared in the mission planner so all feedback welcome.

It actually has some additional changes beyond this fix:

  • compiler updated to 4.9.3 (code runs slightly faster than with older 4.7.2 compiler)
  • TradHeli changes ahead of next round of beta testing (should not affect multicopters)
Thanks Randy for the speedy resolution. Yes your video describes exactly what I did before the crash. I will test as soon as I have my quad repaired. :-)

So here is photo of my build.

and log file

hope link will work


or https://www.dropbox.com/s/gu7qkezv4c1yae6/2015-10-18%2016-29-26.log...

thanks a lot!

Attached are graphs of accels for IMU 1 and 2 and vibration which I believe reflects IMU2 the LMS303D.  This is a 3DR Pixhawk

The accel readings for the Z axis show considerably higher amplitude on IMU2.  It appears the difference is noise / vibration on IMU2. as average amplitudes seem close. But vibration on IMU2 appears factors above IMU1.

The vibration show very low readings on X and Y and higher as expected readings on Z.  On higher motor output / acceleration IMU 2 appears to be clipped whereas I would suspect IMU 1 would be fine.  

Looking at the board layout the LMS is out at the corner of the board where I would guess it is seeing some board vibration.

Is this vibration difference  IMU2 being higher a consistent difference typically seen?  Has anyone attempted adding some vibration reduction foam to support the board corner to reduce this?

The copter seems to be handling well even during acceleration but I am concerned around the clipping seen. This was a 15 minute flight and I am not sure if this number of clips is a serious issue.   Obviously 0 is best.  No  issues with Alt Hold very stable on altitude while flying.

I have done a few of revisions on vibration control and reduced the aount of z vibration and clipping events significantly but may have to do more.

Hi folks,

I'm new to this community and I must say great work done my many here, thank you.

Quick question. I just upgraded from 3.2.1 to 3.3. How do I turn off the low voltage audible alarm while my Pixhawk is powered by USB without having to set FS_BAT_VOLTAGE to zero then remembering again before flying. It didn't do it in 3.2.1. Voltage does read correctly on the HUD so I don't need to calibrate the device.



Very similar than my new build  http://diydrones.com/forum/topics/optimizing-my-first-cuad?id=70584...

I did autotune but without the gimbal in front, then I lower stab pich and roll and rates pitch and roll but pitch stay higher, then I try a second autotune but abort in roll for a lost signal problem and now waiting a calm day to re do for a fine tunning but the copter is flying well, I have to put a cover, look my post. If you want, I can share my actual pids

Randy: It's possible to add to new vers a prearm check against distracted women safe?

If the pilot try to take off in an undesirable mode like Land or autotune for ex. prearm check don't allow you to take off?.

When this can happend? when you have land or autotune in a switch and forgot to unswitch the copter take off completly uncontrolled, autotune goes up and down crazy, fortunetly my copter is designed for that distracted woman and no crash consecuences. :)

What's mean "Err flight mode 15"?

Only a detail, 3.3 is nice. Updating to rc1. Thank's

Never mind. Found a failing USB power supply. Once changed the Pixhawk is now operating as it should, and did,at the correct USB voltage and alarm silent.


"Err flight mode 15" would mean that it was unable to enter AutoTune (AutoTune is flight mode #15).  This could happen if the vehicle wasn't in AltHold when you tried to engage AutoTune.

Many thank's Randy, that's explain all; I notice that when the copter can't engage one mode, becomes crazy, I observed in 3-4 oportunities, It's possible to change something in code if copter can't engage a mode stays, for ex in the last mode that was flying well and no become crazy? I observe in the two copters and with APM 3.2.1 and 3.3; only to take in mind, we have to pay more attention what we are doing when we fly too ;) .

Thank you Cala for your answer. I would be grateful if you could share your PIDs. We've got different props but i thing pids could be similar (not equal).

so if i'm flying with gimbal should i adjust pids manualy for only one axis? for example first for pitch and than for roll?

how to start? First from P? or I? or D? or Stab? :) a lot of question for such a "little copter":)

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