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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Thanks for the clarification. Wasn't sure if George-Kelley was advertising a different radio, my apologies.

It's surprising that it isn't that expensive?

My radio of choice previous was an Aurora 9 which was expensive and limited in functionality as well.

Thanks for the information.

16 channels haha wow

I know your pain. :)  I fly Futaba most of the time.  The nice thing about these less expensive yet packed with features Tx's that are coming out is that it's pushing the big name players (Aurora, Spektrum, Futaba, etc.) to reconsider their offerings and to pay attention to what the consumers feel is important.


Thanks Dave,
I will have a look as soon as I get home.

And sorry for the capital letters.

Yeah I get that. Hitec is a really good company and I hope they match the competition.

Thank you very much for your help, I really appreciate it.

I was in chat with a few people in a German forum and their guess is that the flightcontroller has loosened itself, a motor mount got twisted or the "Vortex Ring State" https://en.wikipedia.org/wiki/Vortex_ring_state is the cause. Will check tomorrow and am curious about what you think it is. 

From your last log file of the actual spin out your RC Out 1 lost traction causing the value to max out, see graph. I would just hold down the quad and test the motor using the Pixhawk motor test at 100%. I don't know what the purpose of the simulator is when you already have one built in. Once you can identify it and reproduce it on the ground follow standard troubleshooting by swapping one component at a time. Don't over look the power distribution board. I just had an integrated one go bad on my Tarot 680 Pro hex driving me batty for a few days. One motor was slipping poles at > 65%. Good luck.


It's not Vortex Ring State. Something much more dramatic.

Vortex Ring State causes your drone to 'sink' like a yo-yo, even though you give it full throttle to pull out. (until you bounce, stably, off the ground, breaking the vortex ring state, followed by your drone shooting right back up into the air). I've had it, and there are videos on Youtube.

In your video, just before the onset of chaos, it sounds almost like a snapping sound. Can you be sure the broken-off motor in your 'after' pic broke off on contact with the ground (and not in the air?). Even if it dangled, still 'wired up', all the way to the ground?


Can the same principle be applied our custom EPM which myself and Andreas are working on? (which will have UAVCAN).

Hi Dave,

This is an unusual log. There is no obvious motor sync issue or any sign pointing to one motor being lost. The closest to this I can see is that Motor 1 appears to be working a little harder than the rest but this is probably just due to an offset CG or that motor having a slightly lower kv than the rest or something similar.

What this looks like to me is one of your motors has rotated during the full throttle burst. This has then caused a yaw that the controllers are fighting by dropping motors 3 and 4 to minimum. The thing that makes me think that this is the case is that motors 1 and 2 are almost equal suggesting that neither one is bad.

If you have a single motor out situation then you normally see loss of roll and pitch control with a single motor going to maximum.

When you looked over the copter after the crash was any of the motor mounts able to rotate on the arms or needing to be straightened. There is a 1 in 4 chance the motor that rotated is also the one that broke in the crash.

Does any of this match what you saw in your copter as you fixed it?

I tried twisting the mounts and it was impossible to turn them (it was also impossible to turn the mount that got twisted (see photo on the tree stump) in either direction). I really applied a lot of force while my brother did some shocks with a little hammer. if any of the mounts would have been loose, we would have discovered that.. the flight Controller is also fixed. 

also the broken off mount was still in its place (could see that while looking at the remaining plastic part). 

what could be: it was cold that day (around 0°C)  and maybe it was easier to twist.

will put it into the fridge and try again. 

thanks, will try as soon as I have time

I am sure the motor mount didn't break in the air. I would have seen this

hey, I am using a PX4v1 variance board with only EXTERNAL compass present and when moving copter in roll or pitch axis I get "compass variance error". I've triple checked my compass orientation and calibration values are all sub 50. Could one of the devs advise when "error compass variance" can be triggered besides when two compasses do not agree? 

Thank you! 

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