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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since your running 530kv motors with simonk firmware esc the sync issue is very possible. That spin was like I have never seen before. I would highly doubt that any SW issues such as EKF would cause that type of spin. Highly doubt it.  If it was a flyaway maybe even a high pitch or roll uncontrolled but that spin no way.


Is this the file I need to direct APM P2 to install in my quad frame / pixhawk to test boat mode? ArduCopter-v2-2.px4

Here is a log of the Copter flying perfectly fine!

Had to rar it because otherwise it would be over 7mb.

didn't have a smaller log with active GPS.

Thanks for your efforts!


how can I reproduce this type of error?

would you recommend BLHeli then?

I first want to find out the issue of the crash before changing anything.

First I highly,highly recommend BLHeli for those motors. Second yes you can recreate it if its an issue but not sure how since I have never had that problem and have always been using BLHeli  Never had to search it but I have heard that you can recreate it. You can also improve it by lowering the PWM frequency I believe with RC_SPEED parameter or something similar. If I were you I would flash BLHeli and that way you have nothing to lose really. And do more tests with props upside down.

If it is a sync issue I am not sure how you can actually find that out from logs. Since its from ESC onward and pixhawk does not have visibility there as far as I am concerned.

hey, you are of course right but it's really strange, that it flys fine and from one second to the other it just fails.

I am also very new to the logging thing and just did basic checks before. Therefore I also don't know what to look for.

The props were all tight!

What vibe levels are ok? Do you mean the VibeX, VibeY, VibeZ parameters?

The high z vibes are from the landing, I guess.


ok, thank you very much for the information.

I will now first try to recreate the issue by full throttle individual motor tests, let's see how that ends..

you can try giving your ESC+motor extreme change of throttle input. if there is out-of-sync issue waiting to happen, these test should kick them right out!

make sure you use your fight controller hardware to drive your ESC/motor speed. for making sure the signals in your test-bench is exactly the signals during actual flying.

I had a crash with my big copter also due to out-of-sync!! the ESC was DYS simonK 30A! since then I bench-test ESC for checking any out-of-sync hazard.

you may check out my video on out-of-sync test: https://youtu.be/NfBgwYjyU1k. hobbywing Pentium pro 30A is also unhappy with my copter! while hobbywing x-rotor 40A works perfectly and it is "certified" to be in mid-air with me ;)

Saw this over at RCG


If you're running BLHeli and 14.2 then you need to upgrade to 14.3

"I've just read that 14.3 is out due to 14.2 having motor glitch issues near high throttle. Check it out."

I´m quite sure there is no problem with your esc. While the coopter descends all RCOUT channels are close to each other

and the copter doesn´t flip. It follows the desired attitude quite well:

I think there is something wrong with the IMU of your AUAV. In the ATT readings there is no sign of the spinning we can see in the video. Looks like the FC tried to compensate a wrong detected spin from the IMU:

Hi Dave,

The log you provide doesn't appear to be from your crash. Can you please give us that log.

Hello, I think you maybe downloaded the wrong log.
After a request, I posted a log of the Copter flying OK:
The crash log is in the first post:

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