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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vibration levels abit high but there was a 23mph gust winds 

vibration within normal levels on not so windy days


My setup
17x5.5inch props
390kv motors
30amp Simonk afro esc
10000mah 4s
Pixhawk 2.4.6
Flys for half an hr

ok thanks yea I reduced WPNAV_SPEED_DN to 4.0m/s only and now it seems to be working ok, it slows down nicely at about 10meters and lands softly....thanks Rob

Nice setup but it looks like you push the quad speed envelop to hard. Theoretical max propeller air speed with lowest measured bat voltage approx. 13.6V with 390kV motors and 5.5 inch prop is approx. 12.3m/s. To be able to move air faster increase voltage or change motors and propellers

Hi stubugs,

Sorry, I need a data flash log.

Thanks I thought it might be on limits of the motor and props don't really want to go any more power or I'd loose flight time

Thanks for looking into Rob! But when I use prevuious version 3.2 with this coaxial octorotor everything all right (I didn't change battery and didn't calibrate ESC's). I change only version APM. With 3.2 I can control multirotor. With 3.3.1 it flipped over.

I don't see anything in particular wrong.  I'd recommend trying a few things:

  • re-calibrate the ESCs
  • do the motors test to ensure the motor order and direction is correct (check the props too!)
  • if the above doesn't help, try going back to Copter-3.2.1 (it's still available through the MP's previous firmware link) so that we can be sure it's a firmware issue.  If Copter-3.2.1 works but Copter-3.3.1 doesn't then it's likely a firmware issue and we can look into it further.


It depends upon the FS_BATT_ENABLE parameter.  Probably best to peek at what that is set to.

Thank you for your help, I'll try to apply the strategy that you proposed.

Just a quick question. What did you mean by the following?

Check to make sure your copter is stable when quickly rolled and pitched to 45 degrees and the stick is let go. Don't hold the stick to build up speed, this test should be done as quickly as possible.

Should the quad withstand when I do the same but speed it up significantly first?

Hey Randy,

I've been testing the V2 via PWM connected to the Pixhawk (using master branch). I also see the jump, often to 12.02m. I also see the PX4Flow Sonar jumping to 12.02m.

Did you guys also see the jump via I2C, or only via PWM?

hi please find attached log

many thanks stuart


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