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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    • Plus 10 !!  Yes I think it should named 4.0 just the facts .. dropped APM Also EKF on as default ..etc .. as you guys say there has been a lot of changes .. why not let APM 8bit have .. 3.2.1...2..3..4..5..  etc and 32bit controllers Have 4.0 ...1..2..3..4 etc 

    • That would be a great idea.

      I think its ok to go for a new major relase just because you drop APM support.

      ATM it is allready confusing which Mission Planner works best with which firmware.



  • Is RC2 still in time for upcoming weekend?

    • Developer


      It's not looking great for this weekend.  A lot of changes have gone in over the past two weeks and there have been some complaints within the dev team that it's become very hard to get the EKF position estimate to settle so that the pilot can enter Loiter, etc.  We need to resolve that before we push it out or it will just annoying everyone far too much.

      • @Randy

        Thanks for letting me know! What this EKF problem is about? I am just finishing my new copter, including landing gear. I planned to use the RX/TX for that but with the new features I would like to plug it on the FC. 

        What nightly build you would suggest with working auto tune? I want to do the maiden flight at weekend

        • The problem is basically trying to walk the tightrope between EKF initialization being too strict and taking too long.  Or being too lax, and having bad initializations leading to potential crashes.

  • This post is actually about an incident with a 3.2.1 large quad, but the fix should go in the next release. I have been flying a very large 14kg quad and all was going rather well with the exception of a lack of power. But what happened was avoidable by myself and by the firmware. 

    I had a brown out due to a bec on the servo rail providing voltage at 5.8-5.9 instead of the 5.5 it was supposed to be putting out. Running the auto-analysis in mission planner never raised any red flags about this high voltage. 

    I could have prevented the total loss of control by having a second bec providing power via the pwr module port, but I did not. Live and learn. 

    What I would like to see is a VCC failsafe. for instance, if a bec is providing power via the servo rail and is going above the 5.7v allowed it should trigger a warning, and not allow you to fly the copter. This failsafe can be manually overrided in the parameters, but for the casual public it should always be on. Maybe a warning at 5.6, and then completely prevent arming at 5.65?

    Also, why would the auto-analysis not warn me of the high voltage?

    Thanks for all your work! If I could write code, I would be all over this project.



    • 14kg quad?what motors is that?

      • Using u10's on 12s. but I am upgrading to u11's now. U10's were a little bit underpowered.

    • MR60

      Hi Craig, sorry for your crash.

      Your idea for a servo rail voltage failsafe is a nice one. However it would not have saved you. The fact you would power also via the power port would not have saved you either. Why? Because if you get a voltage above 5,7V (short burst spikes for example which are frequent if you connect servos on the servo rail), Pixhawk will protect itself by shutting down. 

      So the only good way to avoid your crash was to follow what is written in the manual and plug a zener diode (trimming any spikes above 5,6v) on the servo rail.

      Hope this helps,


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