Copter-3.3 beta testing

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!

You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –


  • anyone have this???

    thoughts... settings etc etc.. mods youve done...??

    i have one flies pretty good.. getting alot of errors though mainly variances on the compass.. but ive removed the checking feature on that .. if i turn the copter by hand left and right it goes to a green light.. kinda weird... but thats indoors.. im going to try 3.3.2 rc 2 outside tomorrow.. i re set everything from compass rc transmitter even esc calibration.. to make sure im good..

    just wondering if anyone has it what you think etc..

    • T3

      Be careful with the built in buzzer. It may interfere with the Accels and the compass.

    • Developer

      I've got one but I've only put it through some bench tests, I've never actually flown it.  It seemed ok to me except it doesn't allow easy connection of the ground wire to the ESCs.  We recommend connecting the signal and ground wires for all ESC to the Pixhawk because without it the ESCs can be confused about the voltage coming across the signal wire which can lead to ESC reliability problems.

      • Altimeter, geo-reference, laser range-finder

        When a laser range-finder is used is it possible to use this altitude as the default for the geo-reference process.

        As I understand, currently laser-altimeter is not used for auto missions, and probably either barometric or GPS is used for geo-referencing.


  • Moderator
    Hi Cala and Goran
    Thanks for that. So is rc2 considered safe and stable to use? Is there an expected release date?
    • Developer

      I was planning in pushing AC-3.3.2 as the default over the weekend but got caught up with the xracer so I'm just reviewing the support forum and this thread to ensure -rc2 hasn't caused anyone troubles.

      It's not too different from AC3.2.1 so I think it's generally safe to fly.

      • T3


        have you made any tests so far regarding the ICM-20608/MPU9250 and 4kHz sampling to eliminate the need for vibration isolation? ;-)

        Looking forward to AC 3.4 (3.5)!

        • Developer

          I haven't done any tests with the accels running at 4kHz but it keeps coming up in the discussion with Tridge and Paul Riseborough so I think it'll happen at some point in the next couple of months.  Both the XRacer and the NAVIO+ have this IMU and hopefully most manufacturers will move to this IMU sooner or later.

        • Are you referring to Linux rt AP like a Pi2 Navio+?  This would be nice to see.  Just got one : )

          • T3


            I was referring to Randy's comment about the XRacer. It is the first autopilot of the new FMUv4 Pixhawk generation (see: and and it is already (partly?) supported in the master branch. So it will be interesting interesting to follow the development.

            And since the Navio+ also has an 9250 on board...

This reply was deleted.


David Hori liked Isabella Domi's profile
gotham liked gotham's profile
Dec 3, 2020