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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The motor imbalance is quite easy to see from the dataflash logs.  Just take a log from a vehicle doing a regular hover and plot the first 4 channels of RCOU message (assuming it's a quad).  If the distance from the highest to the lowest motor is over 200 or 250 then the motor imbalance could be the cause.  Perhaps one of the motors is tilted.If you post a dataflash log I can peek at it if you like.

hi randy,

that´s sound interesting to check the tilted motors.

can you explain it with a picture. attached is a log of me. it´s 3.2.1. i hope it´s ok in this thread.

thank you very much


Sbus out is not implemented yet. Just make a Y harnes for your sbus. Also, it is much better to use sbus ou pin for RSSI so you have that info on your OSD. 


I'm unable to use my tarot t2d gimbal with 3.3 on pixhawk. I have been using it connected directly to my rc on channel 6. Today, I setup the camera gimbal on mission planner to RC9 output / rc6 input according to the wiki. The gimbal initializes with the blue led steady ( no signal )  and the cam pointed to the front ( horizon ). When I press the motor switch , the blue light starts blinking and the camera turns downward, but I'm unable to control it with the RC6 switch.

Could someone confirm that it is working with 3.3 version and perhaps point me to a soution?

Many thanks in advance

6 flights today with my rebuilt copter.
Everything is fine.
Good to go!

I think Robert once said that it was working. Maybe is not so difficult to implement. I would also be saffer than using a Y cable


Here it is for the log, it shows an imbalance of about 100pwm which is fine.  I encourage you to try it yourself though, it's really very easy to produce these types of views.


  If you get time, would you please look at these Auto Tune results for my latest quadcopter build? It's an H4 Alien 680. The props are APC 13x5.5 MR, smaller than desired, but I could not find the adapters for the 14".  It had one squirrely event during roll while AT, but other than that it went smooth.  

Why is the Stab Pitch and Roll so diverged? The COG is darn close, and it seems to fly ok, although only flew it for a few minutes in perfectly still winds :)

Link to flight log


An observation.

Yesterday I tried Auto Tune. The copter would not hold altitude while in Alt Hold, which is commonly reported by many. The AT was aborted and I discovered the vibration levels had worsened.

Today after improving the vibration levels by > one order of magnitude, during AT the copter held altitude much better.

Confirmation bias or a connection?


Great that you got the vibes reduced that much.

Bad vibrations will certainly affect AltHold performance.  It's absolutely critical and we recommend people designing/building copters to check their vibration levels (see First Flight section's Measuring Vibration wiki page) and the live vibration monitor added in Copter-3.3 was added to try and make doing this a little easier.

Copter-3.3.1 is out as the official release now.  Thanks for the confirmation from Miroslav, Yssaril, RandyB, JoeG, Stephan and perhaps a couple of others that -rc1 seemed ok!

Thank's Randy, we don't have to change rc1, it's the same no?

Another thing, when I installed the 3.3 with pix my OSD read all in 0, I have to change sr values before some reading, now I noticed another persons with same problem, perhaps it's usefull to have the correct SR values for OSD as standard params not to have that problem? or if you are not using osd you need different params?


Thanks for all the Dev's work on the new release.

So I previously was using 3.2.1 and it was working.

I now loaded 3.3.1 on my PixHawk on my desk, only using my USB cable for the power to the PixHawk (as I have often done).

The firmware flash seemed to go ok. I power cycled.

I keep getting errors that I don't remember seeing before:

PreArm: Accelerometers not healthy

So I went to do the Initial setup, and tried the Accelerometer calibration.

Then I get this error:

Place vehicle level and press any key.

Initialising APM...
Initialising APM...
accel[1] not healthy
Calibration FAILED

Ok, what do I do? Why do I get an accel[1] not healthy? I can't remember ever seeing this before.

Or, MUST I test this with a flight battery, and not only powering the PixHawk with my USB cable?

Thanks for any hints!

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