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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It seems it will be solved in the next release

I didn't get an error message; I got a compiler error.  config.h says that class 75 is ok to run 3.3, but the code wasn't written to support it.  I'm just curious which was the error.

The APM boards are HAL_CPU_CLASS_16, not 75.  Config.h explicitly allows cpu class 75 for v3.3, but the code wasn't written with that in mind.

I'm just curious if they meant to allow it, and then didn't take care of it properly, or if it wasn't supposed to be allowed in the first place.



Thanks for finding the specific compile issues.  This is more of a dev question so it'd be better to bring it up on the drones-discuss email list.  I think we just don't know if the EKF will function on the FlyMaple (and similar).  If it can run the EKF at 400hz then we can easily modify those #if lines that you've found so that it compiles for the FlyMaple again.  If the CPU isn't up to the task then I'm afraid we will be forced to drop support for the board and I'll modify the #error message so it pops up the failure for anything with CPU_CLASS < 150.

The timing on the board can be seen by looking at the dataflash log's PM message.  There's a number of long loops and maximum loop time.


may have found an anomaly using RC 7 in GUIDED mode:

When radio is off, everything works okay.

When radio is on (flight mode switch set to GUIDED also) motors start spinning fast when arming through mavros. My RC has throttle to medium as default, so tried pushing throttle to zero. This actually made motors spin even faster. Logs show RCin as steadily climbing when RC is on, and as zero when RC is off.


Hi, i fly 2 weeks on 3.3 RC 7 all is great but the pixhawk overwrite the m8n config and i must wait 10 minutes for hdop under 2,3 with 3.2 i wait at same day 10 minutes earlier 3 minutes for hdop under 1,8.

Sorry for my bad english.

3.3 RC 7 is pretty cool only gps is extremly slow.

I have configure ublox manual over passtrough all is fine 2 minutes for hdop under 2,3.

When i disconnect the battery for 20 seconds i wait 5 minutes an have hdop over 3

In u center i see all my config is @ m7n settings this is bad


Thanks for the report.  Any idea which settings are being changed that cause the slower lock time?  Would it be possible to run back-to-back tests with AC3.2.1 and AC3.3 with the Log Bitmask set to "Log while disarmed" so we can see the difference?

Sorry to be annoying but we have seen this type of report with releases in the past and often it's comes down to environmental factors that happened at the time of the firmware upgrade.  Still, that may not be the case this time so if you have some more info that would help.

By the way, AC3.3 allows controlling some settings of the GPS using these parameters:

  • SBAS_MODE : allow enabling/disabling SBAS
  • MIN_ELEV : minimum elevation of satellites above the horizon


If you have dataflash logs that'd be great.  The pilot's inputs should be completely ignored in Guided mode with the exception of the yaw input so it does sound very strange indeed.

i ran 3.3rc7 for 20 flights or so and also with an M8N and didnt experience any of the issues that Dennis is seeing....I actually ran with two GPS, M8N as primary and 6H as secondary


For sure it depends on your location, but 10min and even 3min sound too high. In Germany it is always < 1min with an M8N - no matter is AC3.2.1 or AC3.3. So maybe something is wrong with your module?!


By the way, in the dataflash log's UBX1 and UBX2 messages there's some additional info including a jamming number (see field "jamInd").  Not sure but these may also provide some additional information when the GPS signal is facing interference from nearby electronics (like FPV equipment).

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