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 Andy,

The D term filtering is something we have been doing from the very beginning (when we put the D term in) and my reading of their thread suggests they may have used our numbers as a starting point. It was only recently I made it a settable variable to ensure we could get the most out of the faster quads while ensuring the larger quads could be kept low on noise.

The reasoning behind the interrupt based control loops is also something we have been aware of and using for a long time however the process of squeezing the most out of the APM has meant we had to make some compromises there. I have been talking to the other devs about restructuring the way the fastest loops are run to keep them closely synchronized with the reading of the rate gyros and outputting to the esc's. Our setup is a little more complicated because we have multiple sensors running at different rates and therefore we need to be careful how we do it.

There is a lot of great engineering going on in all the flight controllers and it is exciting to see everybody try to get the most out of the technology!!!

Thanks for bringing this up, it is always good to have this stuff highlighted in case there is something we are missing!!!!


You can download it from http://www.rappens.se/2015-09-28%2016-53-44.zip , 8 MB so it is to big to attach here.

I analyzed som more and I think it stopped and did some yaw back and forth some more times during the autotune?


Which is precisely why I think you should be able to disable the internal.. maybe you can now and I missed that? I have often gotten the compass's inconsistent warning. Seems like if I could turn the internal off it would be beneficial. There's no failover for added safety anyway that I'm aware of. 

I've had great luck with the mini apms v3.1 on 250's. Just finished building my 4th one and they fly really well all in all. I am thinking though of swapping this one out for a hawk lite before I sell it though just to see how different it flies.

Hi Craig,

I would be very interested to hear how they compare!!!

Please give me feedback on my FPV racer blog page if you don't mind.


+1 - I also would like to have an option to disable the internal compass. I believe it would be beneficial to the system.

it just did it again today, always MAG2 on Y and Z axis only, while MAG never shows any problem...also notice how it fixes itself halfway thru the flight.....is MAG2 the external or the internal compass? 

i think there is an option to disable each compass....but which one is MAG2? I find it difficult to tell if thats internal or external

Hi Leonard- Yes I love good news like this :D

I sent you a message here with some added info which will hopefully be of help in advancing the acro capabilities of AC. I would not have bothered to send I did not feel it was significant.

PS it would be great to have an easier method of calibrating ESCs -  components like motors and ESCs tend to get swapped more often on racer / warp quads due to damage and over-use.

I understand that 1 is the ext compass

Is 3.3 out?
Checked in MP for beta FW and I got "APM:Copter V3.3 Quad"?
Or a bug in MP.


I think it´s out since 14 hours.

APM:Copter Release Notes: ------------------------------------------------------------------ Copter 3.3 29-Sep-2015 / 3.3-rc12 22-Sep-2015 Changes from 3.3-rc11 1) EKF recovers from pre-arm "Compass variance" failure if compasses are consistent ------------------------------------------------------------------

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