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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Thanks for the replies gentlemen,

The problem was fixed by Brad's suggestion. Working on 3.2.1 but not on the latest really confused me.

I really appreciate your help.



The new RTL_CLIMB_MIN parameter made me think of this.  Not that I plan to try this, but someone will probably do it by accident eventually.  What happens if your RTL altitude parameter is higher than your geofence altitude parameter?  This would be an operator error in configuration, but curious what would happen.  What happens if RTL_CLIMB_MIN causes you to climb higher than the geofence altitude?

there is something odd in rc8 I think in how it treats IMU1 and IMU2 data.

Is this graph supposed to be normal? Do you se how IMU2 data spikes over around imu1 data? X is red for imu1 and green from imu2 , blue is for imu1 and pink is imu2 data.

I just do not remember rc7 doing it like that. am I wrong?

Randy, thanks!

Yes, makes sense. I need to find more time to get more familiar with the code.

Hi Wilson,

at least part of the problem is "Wires run in-between, touching both pixhawk and minimOSD." Maybe you can relocate the MinimOSD and some cables so the Pixhawk has some more freedom.

And you should also think about moving the buzzer a litte further away from the Pixhawk.

Best regards,


The following issue has been observed with RC-8:

-  When going from inside to outside with the Pixhawk already powered up no issues. 

-  With pixhawk powered off, going outside and then powering up, sometimes bad Gyro message, and compass variance errors appear. 

-  The change in temperature is ~30-40Degrees F from inside to outside.  

-   Repeating the same process except letting the pixhawk acclimate to the new temperature before powering up. no issues. 

I do not know if the Gyro message and or compass variance error are purely coincidence or not. Should the pixhawk be allowed to adjust to temperatures from location to location? can these temperature swings cause gyro / accelerometer errors? should the gyro's and accel be calibrated in the highest temperature area or does it matter?

Secondly after running Autotune and observing the ATUN data from the log file. I noticed it only provides Atun: RP and RD values. Does the autotune process not test various Rate "I" values? I know that following a successful autotune the rate P and I value for each axis always match. Should everybody expect to adjust their rate I value following autotune or does rate I typically not need to be changed from Rp for the average multirotor?


I had suspected this was a 3.3 only bug and Mark's experience seems to confirm that.

I'm guessing some timing changes exposed this latent race condition sometime in the 3.3 rc series.  In any case, I'd consider it a regression and perhaps you will want to review this PR prior to the 3.3 release.





It'll stop that the lower of the RTL_ALT and the (FENCE_ALT - FENCE_MARGIN) altitude.


Yes, as you suspect using ch6 to "tune" the wp-speed will overwrite the do-change-speed command.

There are a couple of to-do items (here, here) on the issues list to allow setting the speed-up/dn but just haven't gotten to it yet.


That's an interesting report.  Yes, the temperature change can affect both gyros and accelerometers.  We've seen gyro drift of up to 5deg/sec in Planes caused by temperature changes.  As you've discovered, if you let the vehicle sit there for a bit it will learn the new offsets and you should be able to arm and takeoff.

The compass variance could possibly appear because the gyros and compass info become inconsistent but we'd need to see a dataflash log to be sure (make sure to enable logging-while-disabled).

One issue is that the mission planner displays warnings for a minimum of 30seconds.  This can make it appear that issues are lasting much longer than they actually do.  There's a to-do item for all the GCSs to improve reporting of the EKF's state.


Yes, in general we see that IMU2 has higher noise than IMU1.  We think it's a property of the sensor itself.

Thanks a lot Thorsten ^^ Let me try that~

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