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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I have a Storm32 board and the issue with the serial protocol is defenitly not fixed in RC 10.

The only option is to downgrade Storm32 firmware to < 0.78.

Maybe some features work but the channel control (Yaw or tilt) does not.


Thanks for the report.  I'll bet that's caused by the slight change in the shape of the pwm->thrust curve.  If you'd like to confirm (I'd kinda like to know actually) you could try changing MOT_THST_EXPO from 0.65 back to 0.50.


This can be caused by the configuration messages from the flight controller to the GPS not getting through.  It may be a one-time thing or it may be because the GPS cable has been damaged.

This weakness has been there, as you suspected, since we changed the hdop value in -rc8.

It's possible to add a check into the driver and/or it possible to update the GPS configuration using u-center to specify the dop message is required so that it's sent even without the flight controller asking for it.

Just upgraded from rc9 to rc10 and a funny thing happened.  Before I could load 10 and had the USB cable plugged in the failsafe went off.  Very load and scary.  Unplugged the USB cable and plugged it back in and all was well.  updated to 10 and did a test flight.

Like the serial ports coming on right away now.  Use to have to wait a half a minute or so for it to go active and sometimes not at all.  Now it seems to be right there.

Test flight was good as always.

Hi all,

Sorry for re-posting several times on this forum as I was unable to catch attention from people ^^!..

Would anyone mind to have a look into my log? It was a flight with 3.3-rc8. During battery failsafe LAND, my copter didn't land straight down but leaned forward instead. 

In this flight I was hovering my copter few meters above ground, trying to deplete the battery completely to test its flight time.

When battery fail-safe kicked in, the copter gradually pitched forward by itself. This forward-pitching was not commanded by me. I tried to pull it back but it didn't respond. It finally landed into a rainwater drainage few meters in front of me. 

My FS_BATT_ENABLE was set to 1 so I expect it to land vertically down. 

Following I plot my pitch input (RC channel 2) vs. DesPitch. When battery failsafe kicked-in, the desPitch drifted away by its own and didn't follow my pitch input.

Does anyone have idea why this could happen? I was flying in alt-hold mode immediately before BATT_FS kick-in.  

And does "BATT_FS LAND" accept pilot input during landing?

I have attached log in the following link. Very much appreciated if you could have a look at it.


Thanks a lot for your help,


No promises on the serial interface working but the MAVLink interface should work although I have not tested it really recently.


I guess you mean the battery failsafe?  I think that means that it did not detect that the USB cable was connected.

Are you using a Pixhawk or some other board, maybe an AUAV board?

The battery failsafe is disabled when it thinks it's connected to the USB port.  Because of a hardware issue on some significant number of AUAV boards we've made that USB detection slightly more conservative. Previously it just relied on getting the power from the USB port but now it relies on getting both power and succesfully connecting to the laptop/desktop computer.

I imagine what may have happened is that when the USB port was plugged in, it was providing power but for some reason USB communication was not actually possible.

That will be a slightly crappy outcome if we've solve one problem (a work around for a harware issue) at the expense of creating problems for others without that hardware issue.

This was a real Pixhawk less than a year old.  The cable I was using may be the issue since I didn't really see the port show up on the computer.

If the battery fail safe is set to low, you may not have enough power to make a controlled landing. I made this mistake once trying to test max flight time. The voltage dropped to low and the quad nearly fell out of the sky.

I would suspect that you did not have enough power for the quad to respond to your inputs as shown in the difference between the desired input and what actually happened.

I have destroyed enough lipoly battery packs to give up on max flight time. I land at 3.5v per cell and have set a new goal of determining the max usable flight time landing with a 20% reserve, just as is recommended by nearly every manufacturer. Now my batteries last a long time and my quads receives a lot less damage.

I had the same thing  happen.. with an AUAV board..  USB 1/2 way plugged in and it beeped loudly, like the battery alarm.  I re-plugged it and it was fine. 
I'm not sure I'd call it a problem, and would maybe just make a note in the documentation that it can happen if your USB cable is faulty. 

Which log bitmask values should I follow, the ones on arducopter page or those in the MP? Or something else?

I need to use autotune_axes, I'd like to tune roll and yaw, what should I enter? 5?

Are these the values: 1 roll, 2 pitch, 3 both, 4 yaw, 5 roll & yaw, 6 pitch & yaw, 7 all?

I changed MOT_THST_EXPO from .65 to .50 as requested. The motors would not spin until MOT_SPIN_ARMED was at 75 so that change didn't have any effect. Fortunately I was using a GCS at the time this first happened and appreciated that the craft was armed even though the props were still.

I tried to look at the log file for this session but it is 178mb and crashes Mission Planner (or overstresses my PC) whenever I attempt to load it.

I also accidentally powered up the copter and armed it without a SD card installed with no warnings from Mission Planner. I feel sure I got a warning last time I did that.

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