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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Just curious: Where do they place the Pixhawk? :-)

Went out to test rc10 this morning on my PH deadcat running Tiger MT4006s 10 inch props on 4s.  Took right off in althold and stabilize so I decided to run the autotune set at .07 -AGGR.

It took about 13 minutes to tune the three axis.  The motions were much less pronounced than autotuning in 3.2; pitch and roll seemed to be about 15 degrees as apposed to the 30 degree plus when ATing in 3.2.  Decided to land and disarm due to low battery warning.

Swapped batteries, installed Gopro and armed.  On throttle up immediately one motor failed to spool up to full speed, I dropped throttle, but it was too late.  The Vbrain 25a 4-in-1 esc burst into flame.  Fire went out in about 5 seconds with no other damage to the CF framed quad.

Wasn't sure how to set logging but it appears that MP 1.3.31 doesn't like the files.  It will not auto analysis the logs.  Message" Could not add reference to assembly mtrand.dll" followed by "Bad input file".

Am I just snake bit again or is there something in autotuning rc-10 that could have stressed one motor in 15 minutes?

Logs included:

Hi Randy,

Have we got any closer to what to do with this issue?  I understand that the message is ambiguous in APM:Copter V3.3-rc10 but I have not been able to find a way out of it.  Do you have any suggestions as to how to track down why EKF is unhappy?  

I have tried disabling PreArm checks entirely and thepre warning message persists.  The LED shows flashing blue when any GPS-reliant mode is selected prior to attempting to Arm. In Stabilize mode (as expected) the status LED is green and arming is possible. 

I have on occasion seen the Pixhawk status light go green in GPS (Fence enabled) mode if I wait long enough.  Yet the HUD says 3D fix and Sats are >= 6.  

this worked great for me, solve the problem plus love the enhancements!!

Hi Randy...I will make the suggested changes and give it a try, the Pix is mounted on one of these (link below), not sure I can try something better...I have always struggled a bit with minimizing vibes on this copter (Tarot 680). Winds are calm today so it wont have the same issue, but they should pickup tomorrow again....thanks a lot for looking into, you guys are awesome!

one more thing, should I try AUTOTUNE first also?


log from burn up


tune file too large to load

How heavy is your copter? I've found those Qbrain ESCs to run very hot on 4s, maybe the autotune just pushed it over the edge?

I'm running a 4 x 25a esc on a test copter at the moment, and at an AUW of 2kg, and 20A total draw at hover, the ESC gets uncomfortably hot after a 10 minute flight.


I have no way to weigh the quad but it should be close to the 2kg mentioned.  Others flying with full FPV that mine lacks are about 2.2 kg.

It flew fine for about 8 months and autotuned in 3.2.  Since changing to 3.3 I have now lost two motors (just found one on closer inspection) and two 4-in-1 escs. 

So uncertain what the issue(s) is.  3.3, undersized escs or two bad motors.  There are quite a few quads with the Tiger MT4006s motors using 4-in-1 escs.  Most of them are using the Emax 25a, but it doesn't play well with the Pixhawk.

@ Greg

I believe that when you land and disarm you "accept the auto tune" and these values will be used onward. (this is why some people, including myself, just do one axis at a time.)

You said " Decided to land and disarm due to low battery warning." So good or bad you saved the new PID values at that point.

I could be wrong but it worked that way until RC-8 or 9.

Perhaps you could place back your saved parameters before this auto tune and do one axis at a time.



Are you suggesting that doing the 3 axis at one time stressed the esc and that doing one at a time would avoid this?  Steady flying to low battery warning didn't seem to cause problems in the past.

No I am suggesting that doing one axis at a time give generally enough time for a battery to do so. 

- So you take off in alt hold activate auto tune with your pre programmed switch.

- You land and disarm (that save the "auto tune" PID for this axis.)

- Placed a new  "fresh" charged battery ready for next axis.

- Using Mission Planner, change the next axis you want to "auto tune".

And you do the same for the 3 axis. 



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