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 your suggestion - I checked the top rear motor and there was indeed play. So I have that resolved now. A subsequent flight felt much smoother. It still drifts away in Alt Hold with no wind, but it's possible that has to do with CoG. This one has been very tricky to balance.

Here's the log in case you're curious.


I didn't have good luck experimenting with the zeal on two copters; replaced one with 3DR foam, the other first with 3DR foam, than added a cheap pixhawk (although a AUAV-X2) platform type like this http://www.rangevideo.com/vibration-mount/849-apm-flight-controller... . The difference is night and day. It would seem the Kyosho should work good, but it really doesn't.

I still say props are a big overlooked factor in vibration and performance, including auto tune. the video below confirms what I've found to be the case: Tarot props are very bad props, not just for vibration either.  Whenever someone tells me they are having issues, my first questions are: 1) AUW 2) motor 3) brand/size/pitch of props.....then work from there.

Apart from T-Motor and a few others, cheap CF props can be the Achilles heel for flight/tuning problems, at least in my experience with >2.5kg copters. I can take two of virtually the same size and pitch props, one being APC MR, the other Gemfan CF TM style, both well balanced, then do AT on both. Every time the APC props fly better and on descent no wobbles or oscillating, plus better stability in wind. On my 750 Y6, the Tarot props were absolutely horrible; switched to APC, much improved 14" was too small with accessories on and bigger battery, 16" is next size up.....too big. Then tried Xoar....excellent. Now it has T-Motor; best efficiency, not quite as good as Xoar for stability because of the pwm divergence.  

The issue isn't just vibration, but weak design causing flexing from the hub outward which promotes "bouncing" and poor handling. Overpowered copters compound these problems. Note in the video that APC ends up the best in the tests done in terms of vibration.


my 2c

Thanks @DG and @Artem, this is the first I have heard that the Kyosho stuff might not work. I have one of those inexpensive isolation platforms so I may try it.

As for props, the rigs I am testing are all spinning APC MR.



  Are you using a Y6 or flat frame?

For my Y6's, these scales make it very simple to get COG as perfect as it can be.


this guy is a Y6 (X2212-980kv, APC 9x4.5MR, 4S 5000mAh, gimbal/GoPro). I will take a look, thanks!

Do you have pics? Sorry if you already posted, but it helps to visually see a setup.

Here's my test quad aka "Dixie Cup". The landing gear is held together with Gorilla Glue; replacing it with hopefully better tomorrow. It really gets pushed hard.

Currently it has the Gemfan props. Well balanced, but there's always something I don't like about the way it flies. Yet after each new 3.3 rc, I put them back on to test.

I swear the next copter at some point will have folding props. So many I've talked to rave about them.

The sliding rails are intended to accommodate balance by sliding battery, gimbal, landing gear, and frame front to back. It would not come close to balance until I turned the battery sideways (funny looking, eh?). In front is a gimbal, GoPro, FPV camera, and vtx.

and bare frame at maiden before silly sideways battery or gimbal, and with crazy long landing gear when I was testing a 10000mAh; have since come to my senses on that:

The goal with this was so see if an extremely basic, small, portable/foldable Electrohub/hardware store build could be used for serious mapping. Easily repeatable, all off the shelf components for the most part.

Letting it pivot on two fingers it feels like CoG is close to perfect. Yet it really seems to want to drift forward in Alt Hold, but also slightly to the side, which is weird to me. So I may try shifting things back a bit to see if that makes a difference. Any other ideas? I can't move the battery further back without interfering with a prop. Cheers.

Are you rear motors turning the wrong directions?  I've never built up a Y6, but I believe they spin opposite of the front motors.  That would explain the odd motor output imbalance that shows up in your log files.

Yeah that rear prop pair definitely needs to be reversed to reduce the yaw imbalance that results from the reduced authority of the bottom props.

Where do you see the output imbalance? It's set up with a "Y6B" layout (referenced on this wiki page) wherein all top motors turn one direction and all bottoms turn the other. You've got me wondering though, so I will double check that Y6B is selected! (just checked, indeed it is Y6B)

Hi Paul,

It is a trade off between noise getting to the ESC's and latency. Many copters don't see an improvement going from 20 to 40 Hz. If enough people report this as a significant improvement then the defaults will change.

Hi Gregmaan,

Sorry but you will really need to go into detail if you want me to understand what you are seeing.

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