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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Hi Greg,

Sorry to hear about your burnt ESC. I don't believe there is anything that has changed that could cause this to happen.

Hi Wes,

DAlt is what the controllers are being told to do. Alt is the estimated altitude the controller is using and trying to make equal to DAlt. BarAlt is the raw output from the Baro before it is combined with the accelerometers.

I believe we can do better in this area than we are currently.

Last weekend we had our first relatively still day for a while and I thought that I would try autotune again. My previous attempts failed - ran out of battery before finished. I have three quads, a 450, 500 and 550 all now with -rc10 installed and I set the parameters to do just the roll axis on each. The smaller quad ran out of battery after 7.5 minutes without completing roll AT. I normally only ever fly it with that size battery, would a tune with the larger battery needed to complete be valid for the smaller/lighter battery that I normally use? In the case of the 500 quad the roll AT finished near the end of it's second battery (10.5 min). I ran out of time to do any more.

I have a couple of questions. Given both that AT now seems to take materially longer and my recent understanding that each axis is separate, is there a case for automatically saving the "tuned pids" after each axis is complete and then commencing the next AT attempt from the start of the next axis to be done? There may have to be a new parameter value or some other means for the user to tell the AT process not to start again from scratch, but this could be setup at home and then the AT process completed at the flying site without the need to modify the axis parameters between attempts.

Secondly, the time taken to complete each axis has obviously increased, more so if the craft needs to be re-positioned. In a ten minute per axis AT attempt, re-positioning will be needed, I suspect, no matter how still the air. I'm wondering if there is anything particular the user can do in respect of pre-autotune setup to reduce the amount of time needed to complete the process?

Hi Mike,

It is not normal for Autotune to take so long. Can you show me a log?

Hi Greg,

Sorry about your crash....

I had problems with Qbrain in other platforms (32 bit boards.)

I spent one month to understand the problem….really hard….…. After more than 20 crashes, I simulated the problem on the ground …. With physical support one axis platform

And the problem occurs without “loops” too…. With fast commands

So.... maybe is a similar problem.... “frequency”… I don’t know…

and with old APMs boards no problems....

Video with Q Brain (look the video description) 1 year ago….


Video afters change Q Brain



Please could you confirm:


Bitmask: 0:Roll,1:Pitch,2:Yaw
0 None
1 Roll
2 Pitch
4 Yaw

If I select only the roll axis (1) to be auto tune. Then subsequently take off in alt hold and activate autotune until it finishes this axis, Following land and disarm. Is the new PID for this selected roll axis stored or not?

Thank you.


Hi Henri,

Provided you have not turned autotune to the off position then it will be saved.

If I recall correctly WPNAV_UP and _DN used to control the climb rate in althold, this no longer seems to be the case in v3.3, what controls it now?

Stock flashes, no BLheli.

Both HW ESC's are using Intermediate timing. High timing does increase RPM at full throttle.

Pardon, I should have addressed this question to Greg, it is very common for both SK and blheli ESCs to heat up like crazy even at 5-6 amps with pancake motors even though hardware is rated to 40amps... haven't seen stock HW firmware doing this. 

What is the AUW, prop size and brand?

Hi Graham,

I think that the climb rate in AltHold (or any other mode when the Pilot controls atlitude such as PosHOLD, Loiter etc.) is controlled by:

  • PILOT_VELZ_MAX controls maximum vertical velocity in cm/s and
  • PILOT_ACCEL_Z controls vertical acceleration in c/s/s
  • ALTITUDE_HOLD_P  will determine how aggressively ALTHOLD modes will try to maintain the current Altitude.

The WPNAV_UP/_DN params are the climb rates that the controller will attempt to achieve when chaning altitude on its own.  (i.e. You are not manually applying throttle to climb or descend. For Example, during a mission or when changing ALT in GUIDED or during RTL)

CHeck the wiki for detailed info: Altitude Hold Mode

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