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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Are you using the I2C interface or one of the other options (analog, serial)?

If it's I2C then that's only available with Copter-3.3.3 (which is out now).

Hi Randy,

Thanks for the reply!

I used the serial port. 

  • SERIAL4_BAUD=19200
  • RNGFND_TYPE=8 (LightWareSerial)
  • RNGFND_MAX_CM=2500

Checked the Lightware with the analog and with a pc and works.

Just wanted to make sure its fully tested and if anyone else tried it yet.




hi bro, what's Lightware ? using for ?

Flew my TBS Discovery with AC3.3.3, so far, it's stable :)

Hi Randy

and thank you for your grate work.

I installed the version 3.3.3 in pixhwak. Today i had a test flight.The GPS locked 11 sat bat after armed and the copter was in the air I lost the gps and the copter return to  failsafe land. I am trying  3 times with the same results.

Thank you in advance.


pixhwak 3dr

telemetry 3dr 433mhz

battery 16000mah.

gps m8n ublox


It is clear that you have bad GPS reception. It may be caused by GPS receiver low quality, bad cables or GPS jamming if it is close to a transmitter.

Do you have the GPS on long pole above the radios and the FPV transmitter?

With 3.3.2 or 3.2.1 I didn't have the same problem.

No gps problem until armed and after 1 minute flight.

The cabling is not very good. It is better to have them tighten together to the platform, not spread in the air. Use braided shields to have proper cable runs.

To protect the GPS from the inferences can use aluminum foil glued below the GPS body(all the black lower body.


Anyone know what .cpp file has the hard coded rate P limits? Or is this done in Missionplanner? Looking to try lowering the p limit to .06

Hi everybody. I happened to install the Copter 3.3.3 on my Octa-Quad where I was flying the 3.4-dev of January 27th. The system turned to have a poor heading hold (oscillations of even 20 deg) and a poor position hold. I thought It might be due to a magnetometer calibration (as I moved the GPS on the back), so I calibrate it again, but same behaviour. In order to stop the oscillations in LOITER I had to increase the POS_XY_P from 1.5 to 2.5... Is there any major changes that are influencing that behavior? 

I am about to upload the previous firmware and to make other flying test, maybe I could upload a set of telemetry that might be helpful for finding any possible issue

This is a capture of the Heading vs Desired Heading. It happen to get worst in Guided mode

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