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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Hi Artem,

Sorry, Typo. KV

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.

Relationships between PID settings - Vibration - INS_ACCEL_FILTER settings?

Can anyone explain these relationships? I found on my FW-450 with Pixhawk (3.3.2 fw) / RCTimer MT2610 920kv, BLHeli 30A, 1045 prop at default I_ACC_FLtr = 20 and using 3DR foam for FC mounting I have vibration (IMU_AccelZ plot) between -11 to -9 (+/-1g) should be good (at least it is 5 times smaller than recommended) but in AltHold it is still jumps up and down a bit.

On newly assembled nighthawk clone (320 base with APM mini, M8N GPS, EMax MT2208 II, BLHeli-20A) FC set on harder foam and this FC is small and light so not much vibration dampening. At filter INS_MPU6K_FILTER set for 20 vibration between -15 and -5 (AccelZ) with filter set to 15 - vib. -12 to -7 but the flight behavior (oscillations) as if I am tuning PID, very similar to a bit higher values of rate P.

Is it possible to set lower values of INS filter (to get lower vibration) and compensate oscillations with PID tuning?

APM is notorius for vibration sensitivity, I could not get it to PosHold almost at all, Pixhawk is a bit better, but only with very soft foam pad - may be it could be alleviated by FILTER - PID conbination? 

Any Ideas? Explanations?

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.

Thanks randy ^^ greatly appreciate your effort in talking to us **ALL** !!

My flight log can be downloaded here:


I guess the funny error codes are indeed due to some single corrupted values in dataflash log. I can see there is also an abnormal value in CTUN::ThrOut, whose value is as large as 10^36!!

I bought the USB-fpv receiver from the link below, which is the CUAV chinese online store.


The product name is "CUAV VMR32 5.8G". There is one thread on rcgroups advertising it.


Thanks for all the links ^^ Let me also get in touch with Tower guys. Wish some days later I don't have to mount both FPV monitor and android tablet all on my remote Tx~~



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

Hello, I just want to report that today I  finally was able to fly, the weather wasn't allowing.

3.3.2 flew awesome! No issues. Congrats to this great team!

I am having 'Compass variance error' since upgrade to 3.3.2. I was flying beta versions previously with no issue. The problem seems to be worsening as well.


1000mm hexacopter, New Pixhawk (imu failure on previous one), CSG Shop M8N XL (primary GPS), Generic Neo-M7N, RFD900, 1.2 video tx, Frsky X8R rx, 900 mhz gps dog tracker

6s dual 8000mah batteries

AUW ~6kg

It gives no indication of failure at startup, but once I get off the ground in stabilize it will randomly do a roll pitch and then maybe give me a compass variance error and then do a large pitch or roll twitch. I can switch into alt. hold and pos. hold and it will do the same thing. The twitches are getting worse with each flight it seems. I tried recalibrating the compass with no improvement and I just tried switching to the 2nd gps compass (did calibration) and the same results. I'm not very experienced at log review and hope someone can help.

In this log I took off, saw a twitch, switched into alt. hold, pretty sure I heard the computer say 'compass variance error and then it pitched back and left pretty hard. I recovered and land ASAP.

TIA for help!


Look at the compass?_dev_id. My pixhawk have the internal ID = 131594. My external ID = 73225 , it is a genuine 3dr ublox gps. In my conf , the compass_dev_id is the external  and compass 2 is the internal. You shoud set the compass_primary to wherever your external compass is at. Try that and see if helps.

I have never used compass_learn...

Thanks for the advice, I do have the external as primary. I ended up moving the pixhawk and the zubax another 10mm off the deck and it seems to have helped a bit. I did four consecutive calibrations and they were not too far off from each other and passed pre arm checks each time.

Cheers, RB

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