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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Copter-3.3.2-rc2 is available through the mission planner's beta firmwares link. Changes are in the release notes
(https://github.com/diydrones/ardupilot/blob/master/ArduCopter/Relea...) but here they are along with a video
showing the major reason this version is out.
1) Bug fix for desired climb rate initialisation that could lead to drop when entering AltHold, Loiter, PosHold
2) Fix to hard landings when WPNAV_SPEED_DN set high in RTL, Auto (resolved by using non-feedforward alt hold)
3) Reduce Bad AHRS by filtering innovations
4) Allow arming without GPS if using Optical Flow
5) Smoother throttle output in Guided mode's velocity control (z-axis now 400hz)

Hi Leonard,


Is the latest successful tune. This was in pretty quiet conditions.

My other posts:





I think my original issues were because one ESC was badly calibrated. Once I fixed that things worked better modulo the low P values.

Hi Cala and Goran
Thanks for that. So is rc2 considered safe and stable to use? Is there an expected release date?

Hi Leonard,

So the 0.004 value was set by autotune both in roll and pitch. If I do a manual tune on roll then a value of 0.003 seems pretty stable, 0.004 is borderline. So I'm interested in the 0.001 value - that seems way below any setting that would lead to fast oscillations. Is it worth me trying this? Like I said n my previous post the main issue seems to be not having a high I value - that leads to a lot of problems. Also what determines a good stab roll value? In the Dave C method he recommends a value of about 3. Autotune selected 9 in my case - what does this affect and how can I tune it? There doesn't seem to be any way to map it to channel 6.

I attached a log with me manually tuning Roll P from the autotuned values.


Hi Andy,

The low D term is so Autotune can tune it properly. It would be great if you could give it a go. Autotune needs to be able to go lower than the optimal value to find it that is why it needs to be so low.

Based on your issue we are reducing it by default.

If you could take the time to do Autotune in some good conditions I would appreciate it!!


Hi Leonard,

No problem - gale force here, so won't be today!

So just so I get this right - reduce D and leave everything else the same and then run autotune?

Just roll, or roll and pitch? If roll and pitch do I need to reduce D in both before running autotune?

I've just bought some 2200mAh batteries so am hoping I have enough power now to get good tunes everytime.


You are an experienced pilot, nothing is safe and stable guarantee with this toys ;) It's as your oun risck, but if you use the stab release, be carefull to switch from stab to loiter, pos hold, etc., I try many times with beta and the issue go away, but I'm only an user, Randy go to send to stable when he consider safe but really I like this last vers, great dev work. What vers is your last one?

Hi Andy,

Just to be clear. Don't change your tuning parameters of Rate_P_D or any others. What you have done is fine.

I want you to reduce AUTOTUNE_MIN_D to 0.001. This parameter is the minimum D that Autotune can use. 

Does that make sense?


I was planning in pushing AC-3.3.2 as the default over the weekend but got caught up with the xracer so I'm just reviewing the support forum and this thread to ensure -rc2 hasn't caused anyone troubles.

It's not too different from AC3.2.1 so I think it's generally safe to fly.

Thanks Leonard, got it. I'm glad I asked!


The compass variance should only happen when the compass doesn't agree with the other movement of the copter.  So if it was oriented incorrectly that would certainly appear.  It can also happen if there's interference from the motors or if there's metal on the frame that warps the magnetic field.

By the way, the "compass variance" is not actually triggered by having internal and external compasses that disagree.  That situation produces the very similar "inconsistent compass" pre-arm message.


What you describe is planned for Copter-3.4.  I have a half-baked development version that uses the terrain database (fed from the google-earth or other mapping services) but it needs a bit more development and lots more testing before it's ready.

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