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 –


        • Artem,

            I started a discussion on RCG about coaxial efficiency per eCalc authors. I tried various prop combinations and found the most stable to date was using Xoar 15x5 top and Xoar 14x7 bottom, tried different timings as well which did make a difference.

          As you can see, I had the same problem as you:


          Below is with Xoar 15x5 top and Xoar 14x7 bottom. I bought some 14x8 but broke one of the blades and never reordered. I now have genuine T-Motor 15x5.5 top/bottom and it is not as stable; haven't flown it for quite some time but want to put the Xoar 14x7/14x8 on the bottom. One thing I'll say is the cheap props flex way too much and cause oscillations. 

          I also believe the axial distance between the props changes things as well, and with much confidence conclude no two Y6's are the same (had three of them), nor does one size fit all. I'd like to try BLHeli firmware on the HW Xrotor ESC's on this copter. 

          Xoar 15x5 top Xoar 14x7 bottom. Very stable and reduced VRS substantially.


          Link to RCG discussion:

          Link to eCalc essay:

        • Developer

          Hi Artem,

          Sorry, Typo. KV

        • Hi Artem,

          I use 13x5 upper and 14x7 lower. Rcout is almost equal for upper and lower motors.


          • 3702854085?profile=originalThx,  what is your AUW and motor  KV? Thank you! 

            • AUW 2650g

              Pixhawk AC 3.3.2

              Neo M8N

              EMAX MT3506 650KV

              Kiss ESC 18/30 A

              Multistar 10Ah 4s 10C.

              Aeronaut Cam Carbon light 13x5 upper / 14x6 lower.

              ->26 min hover.

              I also tried APC Electric 13x4,5 / 14 x 7.

              Both Setups work fine. I think for an efficient coax setup you need more pitch and larger diameter for the lower prop.

              • Yep,  AUW is about what I thought. Thank you! 

            • Everything I've seen tested so far is either from a test stand of hovering.  Like helicopters, once you start to move and enter ETL (effective transitional lift), a lot of the vortex interference will dissipate.  given the vortices travel downward, I wonder if mounting the rear arms higher than the front arms would help?   Sounds like a job for Simscale : )

              • Its a Y6, coaxial. 

                • Then you'd just raise the single back arm.  Funny you'd mention a Y6, I was thinking of a Gryphon 1400 Y6 with a bent arm on the rear and 6 of the new KDE 8218's.

  • Any suggestions on improving noisy IPD EKF values? It appears that it is mostly related to a Noisy Barometer. I've got vibrations well below acceptable levels. 

    The Pixhawk is housed in an rctimer dome.

    I loose about 5-10 feet of altitude transitioning from hover to directional flight. I've increased EKF ALT Noise to 3.7 and its subdued the rather aggressive drop to a sustained slow drop over about 10 seconds vs 1-2 seconds.

    Still would like to improve on this.


This reply was deleted.


Shivchand Jaysaval liked Shivchand Jaysaval's profile
Aug 25