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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O, ok, thank you Randy for responce. So if compass movement doesn't agree with lets say acc data this message will be triggered as well, correct? 

No problems here.   Stabilize, alt hold, pos hold, auto mission, land all worked fine no issues. 

+1, No more change mode issue


have you made any tests so far regarding the ICM-20608/MPU9250 and 4kHz sampling to eliminate the need for vibration isolation? ;-)

Looking forward to AC 3.4 (3.5)!

Are you referring to Linux rt AP like a Pi2 Navio+?  This would be nice to see.  Just got one : )

Hi Cala 

Yes, I fly OK but I loaded ver3.2.1 after some repairs a few weeks ago and then put it away to work on a project then came back to this and just wanted to catch up. 

The snow will stop me flying until the weekend so I can wait until 3.3.2 becomes the default, Thanks Randy , great work.  your ongoing development is superb. 

The purpose of the simulator was to identify ESC sync issues. They are caused by fast variations of throttle input. With the simulator, I can put out much faster variations of throttle, but it still didn't fail.

Hello George, sorry for the late answer but I was busy working on the copter :D

I also hear that sound and am wondering what it came from.

I agree, that it sounds like something is breaking.

The issue is: I am so sure that the mount didn't break in the air because of the following reasons:

After the crash, the broken off motor mount was exactly where the copter was, so it couldn't have fallen off during flight.

If it would have been broken off during flight (not fallen off fully), the still spinning prop (the Pixhawk was still telling the ESC to turn the motor) would have at least scratched an arm or something but it hasn't.

As you can see, It's just unreal and I can't believe it.

Speaking about the video you posted:

I agree that this is the weakest point of the motor mount (they are out of plastic) and if it breaks, it breaks at that point, but i don't think it can break because of the thrust (also tried it at my bench)


I was referring to Randy's comment about the XRacer. It is the first autopilot of the new FMUv4 Pixhawk generation (see: https://pixhawk.org/modules/pixracer and http://www.auav.co/product-p/xr-v1.htm) and it is already (partly?) supported in the master branch. So it will be interesting interesting to follow the development.

And since the Navio+ also has an 9250 on board...

Hey leonard, sorry for the late answer.

please also read the post I made above (here: http://diydrones.com/xn/detail/705844:Comment:2141745)

the arm that broke is arm 2 (rear left).

To your thoughts at 1:

sync issues were tested at my bench and I didn't find anything unusual :/

Ice could have been at the props but if so, it couldn't have been much, as I didn't fly high before the throttle burst.

Also I put circuit board paint at my ESCs to protect them from any water.

interference on the signal line could have been there, but I don't think, that could be the cause for that sudden failure.

See the above post for information regarding your second point.

One arm was slightly rotated after the crash (maybe 3-5°) but as I said, I couldn't move it afterwards. It must have been from the hard crash.

I have no idea what caused the vibrations :( maybe I just have to live with this not understandable crash of course mostly because the copter was too far away to see the decent good enough to see any breaks :/


the arms are very stiff. however the folding mechanism could be the weak point which allows vibrations to occur.

Hi Dave,

If one of the arms was rotated by 5 degrees after the crash then that fits all the symptoms. I suspect the sound you hear is the arm rotating under the large vibration forces I see in the logs. 5 degrees may not have been enough for me to see the lost lift from that motor.

This may have been made possible because of the cold air letting things move just a little easier than they do when everything is back up to temperature.

You are in good company with that crash, Marco had a motor rotate 90 degrees on a hex. Thankfully arducopter kept is stabilized nicely an he was able to land it without damage.

I think you are safe to assume this is the case and give things another try.

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