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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Here is the log. I'll do another try on Wednesday when it should be less wind here and of course I can do another test when the next RC is out.


Changed droneshare settings. Maybe now? I did change back. Btw, why p limit in mp is 0.2? 0.35 on mine seems to be ok..?

I restarted the Autotune since the quad descended really low the first two times and I didn't remember it doing that on the previous version.

Is there any more information on what changed to reduce the CPU load so drastically?

Hi Kuisma,

Rate D is limited at the lower end to 0.002.

I think I see the problem.... maybe.... It looks like the release went out with AUTOTUNE_AGGR set to 0.05. This tends to be a little sensitive, the default should be 0.1.


Hi Maciej,

The release went out with AUTOTUNE_AGGR set to 0.05. This tends to be a little sensitive, the default should be 0.1.

I suspect we will get a lot of failed autotunes until the next release candidate because of that default value.


I have an older version of Alexmos board. On previous firmware, it was working fine with PWM RC input. The board is connected to pixhawks Aux1 and configured through the gimbal settings in mission planner. In AC3.3rc1, the same setup fails to work. I think it is related to the feature of the firmware that supports Alexmos boards through the serial interface. But my Alexmos board is not capable of Serial controls. The only way that made my setup work is by directly connecting the RC in of the Alexmos board to the receiver module thus allowing it to work with PWM.

It would be really useful to be able to tell autotune what size the drone is and what application it is used for and tune accordingly. I have an 800 and the 3.2 tune makes it far too twitchy for video work. 

I noticed an immediate improvement on my newly built quad. It takes off much more nicely and descent is smoother. No Auto Tune done yet, but just did one yesterday with 3.2.1. Based on comments I think I'll wait.

That's my 2 minute observation report :)

Are there any plans in the future for Altitude Verification/Input using LidarLITE?

I tested 3.3 today with a early model lidar-lite attached using the PWM interface, following the wiki instructions.

It appears to work hand-held (sonar alt makes sense while disarmed.) However, I had rapid, short climbs when switching into alt hold or pos hold.

My quad is a bit heavy for it's size, 400 class, 8" props, 1.8kg but flies fine on 3.2.1. Winds were light and variable.

Here's the flight with Lidar-light active. Here's one without.

Also, I'll add to the report that Pos hold is not showing up as a valid mode, but only with the lidar active.

APM Planner won't calibrate accelerometers after 3.3

I screwed up and started a discussion instead of a reply so copied to this discussion

I am pretty sure this was caused by the 3.3 upgrade.  I have successfully calibrated the accelerometers many time recently and when I tried after 3.3 it times out and will not calibrate.  I hooked up my trusty Iris after several attempts on my 550 and the Iris responded as normal.  I then hooked up a spare pixhawk and uploaded 3.3, attempted a calibration with no results.  Neither unit will calibrate now even if I revert back to 3.2.1.  I took the 550 to School today and successfully calibrated 3.3 with a PC running Mission Planner.  I came home this afternoon and uploaded 3.3 to my Iris and it now has joined the other two in the calibration fail pile.  I am now out of tricks and could use some help.


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