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!

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      • Marco,

        Could you give a more detailed advice on what exactly affects this decent behavior? It worked in 3.2 release, what is different now? What parameters control stability during descent as it is the only situation where this platform wobble occurs?

        • Developer

          Hi Paul,

          Could you provide a log so I can see your parameters and what is happening.

          • Hi Leonard,

            Was there anything obvious in the log I posted?

          • Sure.

            Here it is. I had to switch off hi rate logging as Randy suggested to try to fix GPS issues, it seemed to help.

            If you look at vibrations graph you can see how after 3:30min mark IMU Z accel goes crazy.

            It is what it does at descent. No idea why, it was a relatively calm day.

            If you want the video you can also hear what motors are doing, it does not seem to be normal, IMHO.



      • it is rc8 autotuned setup, in perfect conditions, no wind, with 0.05 setting, done twice to see minimal deviation from first autotune result from second. it is tuned as well as rc8 thinks it should be.

        there are no issues at climb, no issues with horizontal movement in calm conditions.

        with moderate to strong wind circle mode causes similar platform shakes at certain angles, and same shakes always at descent. from what I remember it was not doing it like that with APM and 3.2. vehicle is well balanced and has no issues.

        what specifically 'bad setup' means in this regard? what can be adjusted to fix this?

  • I recently flashed the 3.3rc8 and it has been working great for me.  I had some tip overs however because my landing gear were to long and wobbly.

    No that is corrected.  

    the propeller tips were a little bit chipped and worn though and I wondered what my vibration level was.

    It seems to fly fine, but I don't want to run into an unexpected situation due to vibration.  

    So, I weighted it down with about 15 lbs of steel and performed the test in MP.  This copter is an animal, 15" blades, 380rpv pancake motors on 6S. It is pretty scary even tied down in the living room of my house.  I was afraid to go to 3/4 throttle but I got close..

    I'll post the graph, bit I think the vibration level t looks like it is within the recommended limit.

    I also looked at the flash log to try to correlate different indicators to try to educate myself on what the parameters all mean.

    I notice, (and see this often) that when looking at the chart produced looking at rcou for example.   It shows mode changes to alt-hold and Poshold even though I was not touching the transmitter and was locked into the compass/motor vibration test.

    What does that indicate?

    the .bin and the graph correlating to the comp mot test



    • Developer


      The vibration levels look ok.  Around 20m/s/s which is maybe 50% higher than my IRIS but still in the acceptable range.  I think that holding the vehicle down may invalidate the testing though, because it should affect the vibration levels quite a bit.  I expect holding the vehicle down actually makes the vibrations higher though so I think it's ok.

    • Sorry had to repost the vibration test graph


  • Any idea why when the copter is switched in to any mode that requires the baro it has a 1 second full throttle climb then returns back to the requested altitude?  It hovers exactly at mid stick in stabilize.  No expos or anything in tx.  I upgraded from 3.2 per the directions and it started doing it.  I did an eeprom erase and started with a fresh 3.3 rc8 and a fresh parameters and still the same thing.  Log and picture are attached.



    • T3

      A first guess since I currently cannot check your log file: is your buzzer located pretty close to the autopilot - or on the same vibration damped platform?

      Best regards,


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