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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Thank you for sharing this ;)

I get same message on original Pixhawk

Thank you for sharing ;)

Using AC3.3-rc8 for the first time, I had a catastrophic failure. In my video here, you can see me doing a manual tune at about 20' alt, when it suddenly locked itself to about a 45 degree angle to the right, not responding to controls, and started sliding down that angle. I then cut the power, which is when you see it roll left and crash. I panicked a little, but couldn't let it continue. It also reported that it was suddenly over 4000' alt, and warned me with Tower audio (connected through Bluetooth, not APM radio) that it was over 400' as it was going in.

Attached is my Pixhawk log in .BIN format. I am not good at diagnosing from logs, so any help is appreciated. My copter is broken with parts on order, but I will not fly again with rc8 until I understand better what happened.


in the air may be a different issue of a dynamic interference, I was getting it from compass on my front GPS unit from gimbal motors, when I moved compass to rear mounted second GPS unit and both compass variance and velocity variance warning messages went away.

but prior to that with a mast mount there were compass variances as well, in any mount locations and I tried several.

other, well, method to see if your external compass is acting of - when you do calibration, look for the shape of the sphere of dots that gets created during calibration to be as ideally spherical as possible. if you see it severely distorted - it means you have something wrong. it also helps to do one calibration with no power to ESC, motors, gimbal, etc secondary consumers, then look at offsets and shape of the calibration, then power up all equipment and do it all over again and compare afterwards.

And even after that, as you can see from my exchange with Doug some stupid stuff still can happen with GPS units, due to power feed quality/filtering or interferences, go figure, and with 3.3 it affects EKF and then affects your drone`s stability.

I suspect a lot of reported incidents here are directly related to less than optimal configuration of external compass/gps units as I saw some weird behavior of my drone during polishing up mount locations and wiring.


ok i undestand, the copter hovers on throut of about 230.

Review a blog I put out a while back.

Bigger isn't quite the right verbiage. What many of us have discovered is that the patch antenna coupled with an adequate ground plan and a decent EMI shield will helps tremendously with 1) receiving signals and 2) reducing EMI or as Randy mentioned, jamming although I prefer to not call it jamming. 

There is GPS jamming techniques in the world which is used by some countries to deny their adversaries the capability to access GPS satellites.  So I really don't count electronics on your drone as jamming.  It really falls under interference or EMI.


I have several GPS units, Lea-6H (oldest model 25mm patch antenna) to the M8T (using ground plane, EMI shield and uses 45mm patch antenna). 


You may not need a large GPS unit on a 250 size frame but more importantly, what type of GPS would you need for your vehicle and it's mission.

Hey, I´m using apm:copter 3.3 rc7 and would test the "hott telemetry" function of my graupner rc.

The telemetry function is included and working on the px4firmware used by apm:copter, described here link.

But I could not enable this module on apm:copter by NSH terminal.

Or is it not included/build on apm:copter firmware?

I´ve found the src on apm:copter firmware here github\ardupilot\modules\PX4Firmware\src\drivers\hott.

Is there any possibility to enable this module on apm:copter?

Thanks for your response!

What this the last beta version of AC3.3 without "Compass Variance" issue?

It is the rc5 or rc6?

I get this message on the ground, without arming, so no any current, no EMI ... just still on ground and if I try to move it - I get warning.

https://api.ning.com/files/Dyivh8oZtEx6vGHrt1Zwkbs7s2lPdbbURjFCtsVp...is this the GPS unit you used? See one in the front. If it is not the one, post a picture of yours, so it can be clearly seen.

note how it is mounted on my drone. pixhawk is also directed correctly toward the gimbal. this location of this GPS unit should use ROLL_180.

Both compasses must be aligned correctly and point in same direction. Arrow on the pixhawk should point toward nose, GPS unit should be positioned as shown.

If drone is on the ground it does not mean there is no current.

If lipos are connected - there is current. There is EMI noise from BECs, there is gimbal motors magnetic field, there are signal wires, there is a ton of things.

In a worst scenario there may be some loose metal bolt close enough to the compass mount.


Motors are off, current is very very low, so EMI almost at zero. On my tests gimbal is off too (hardware switch). So, there is not so many things on idle mode what can impact compass.

All this tiny things you are talking about is nothing compared to the current and EMI on full throttle on the air.

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