ArduCopter-3.1 released!

After months of testing AC3.1 is finally available in the Mission Planner and GitHub.

Warning #1: If the vehicle is left landed (but armed) while in AltHold or Loiter mode for more than a few seconds, the vehicle may suddenly jump into the air the moment the pilot raises the throttle above zero.  The reason is the baro altitude may fall while the vehicle is sitting on the ground.  In AC3.2 this bug is fixed because we reset the target before take-off.

Warning #2: Motors will spin (slowly) by default as soon as the copter is armed!  You can switch this feature off by setting the MOT_SPIN_ARMED parameter to zero.

Warning #3: if you see "Bad Gyro" on the HUD then you may have a blown 3.3V regulator.  See this thread for details.

Warning #4: if you use a sonar set the SONAR_GAIN parameter to 0.8 or lower

Warning #5: Trad Heli users should now connect their main rotor ESC to APM's RC8 output

Warning #6: Trad Heli BUG causes loss of collective control in ACRO mode if swash type set to flybarred (i.e. not flybarless).  Will be fixed in AC3.2.


The major improvements over AC3.0.1 are (full list here):

1. Pixhawk support (Tridge & PX4 development team)

2. Autotune of Roll and Pitch gains (Leonard/Randy)

3. Drift mode (Jason)

4. Improved Acro (Rob/Leonard) and new Sport mode (Leonard)

5. Arming, Take-off, Land in Loiter or AltHold

6. TradHeli improvements (Rob) including:

a) support for direct drive tail rotors

b) smoother ramp-up of main rotor

c) reduced collective for better control in stabilize mode (STAB_COL_MIN, STAB_COL_MAX params)

7. Support for SingleCopter (Bill King)

8. Performance improvements resolve AltHold troubles for Hexa & Octacopters

9. Safety Improvements:

a) GPS Glitch detection (Randy)

b) Motors spin when armed (Jonathan Challinger)

c) crash detector shuts off motors if copter flipped for 2secs

d) batt failsafe option to RTL instead of LAND, gps failsafe option to trigger AltHold instead of Land

e) more pre-arm checks of inertial nav speed,

10. Bug fixes:

a) optical flow working again (although performance is still not great because not integrated with inertial navigation)

b) ROI working (use DO_SET_ROI command)


How to upgrade:
Click on the MissionPlanner's Initial Setup >> Install Firmware screen.  The version numbers should appear as "ArduCopter-3.1", then click the appropriate frame icon and it should upgrade as per usual.

Special thanks to Marco and the many beta testers on the AC3.0.1 thread who put their copters at risk during the testing of this new version and uncovered many problems so that you don't have to!  Here are some of their videos: loiter in wind, patio sonar, autotune, autotune2, roi, beach, acro, vrbrain, tricopter, train spotting, radio failsafe, the tree, double loiter


If you haven't seen it recently, please check out the ArduCopter wiki.


Feel free to post comments below and we're going to use the new APM Forum for support issues so please post your support requests there.

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    • Developer


           That's the classic symptom that shows up in the existing inertial nav when it's exposed to high vibration.  It's somewhat expected that the altitude and climb rate don't match because the complementary filter is trying to make sense of incompatible information from the accels and baro.  It is slightly odd that the climb rate always goes negative in these situations..I'm unsure whether it's an issue in the inertial nav library or an issue in the accelerometer hardware.

           The only way to resolve this on the APM2 is to cut down on the vibration in the frame or adjust the mounting of the flight controller.  With the Pixhawk it should be more resistent because it has dual accelerometers.

      • Interestingly, I got the very same problem on my new Hexa with PixHawk.

        As per logs, vibrations jump on both IMUs. And it looks, like full throttle is given prior to increased vibrations. So it might be, that vibrations are a consequence of full throttle, and not vice versa. However it is hard to say for sure.

        • Developer


          In AC3.2 we have an EKF that can be used by setting the AHRS_EKF_USE parameter to 1 (then reboot the board).  It's not fully tested and I've heard it's a little jerky in Loiter (a problem we will resolve for AC3.2.1) but in any case this is the longer-term solution to resolving the solving this problem which is caused by accelerometer aliasing due to high vibration.

  • Ok Guys I have a very interesting problem most likely to do with the Pixhawk than the firmware .. could also have something to do with the compass cali in MP going bad.. here is my story. 

    Just built a new machine (one of many) Finished set up and it was flying quite well, including a demo to the customer and interested parties.. (copter has been built for weed spraying etc) we were invited to do a demo at Scion Institute the following week , so we went down there and flew , but I noticed GPS was not holding well (copter trying to fly off) and Mag field was too low, so I could not use Loiter mode .. However upon returning home I plugged the Pixhawk (supplied by 3DR) into the Laptop and checked Mag field  and checked Compass .. weird thing was the compass did not seem to be moving correctly in the HUD .. anyway after trying several times to re calibrate the compass each time failing, I noticed the onboard compass was only showing pixels gathering on one (1) axis on the MP calibrate screen .. MMmm, so I though the compass must be corrupt did a full reset and erase and started right from the beginning..once again when it came to calibrating the compass it was only showing activity on one axis on the new fancy MP Cali screen.. So I thought the compass must be DEAD, so I fitted an external Compass and redid the calibration .. having to do include the new  upside down move..and the calibration this time was fine ..I did a test flight and the Loiter held just fine , previously it would try and fly off to who knows where !   So wtf ?

    The mag field was an interesting one too .. I could not figure out why I was only getting 220 - 270 strength.. started trying all sorts of stuff , long story short was I had the short 90 degree mini lead plugged in so I could access it easily .. well due to it being 90 degree plug it meant that the lead had to go around the front of the pixhawk  and terminate towards the rear .. so it lay neatly under my dome, well after removing the extra little usb lead .. the mag Filed jumped up to 680 instantly .. Note: the USB lead was not powered it was just sitting there.. So the lead was affecting the mag field alot ! I will note i had already removed this lead when trying to calibrate the onboard compass so it was not the reason why the compass is not working ..  

    Any thoughts ?? Anyone have similar issues with the on board compass going dead ?  At least you know now what to do the when you see the mag field too low ( remove any thing you have in front of it )  in my case a short mini usb lead.

    Regards Reuben

    • 3702494831?profile=original

      • Developer

        So that looks like very bad offsets possibly caused by having metal near the compass.  The Pixhawk board itself causes quite large offsets on the internal compass which is why I'd recommend always using an external compass.

        Re your work on a weed sprayer.  There is an undocumented SPRAYER feature in ArduCopter.  I've done a videoof the original project I did that prompted this development in case it's of interest.  Basically it allows controlling a pump and a sprayer depending upon pilot input and vehicle speed.

        • Hi Randy 

          Just an Update .. My pixhawk still does not calibrate the internal compass..

          here are some photos of my Spraying copter with interchangeable spray booms and solenoid to switch between different jets..


          • Developer


                 That is super cool.  How are you activating the sprayer?  You know that there's a sprayer library in ArduCopter?  it's not well documented but it can be enabled if you compile the code yourself.

                 We're going to fix the issue with the internal compass not being calibrated in AC3.2.  This affected me personally at Sparkfun because the external compass failed on my final run and I ended up with the vehicle doing toiletbowling.  So I'm highly motivated to fix the issue.

            • Randy,

              Good to see you at SF.  Do you know how many ended up in the water by the end?  I had to leave about 1:30PM.

              May I ask where the sonar is in AC3.2 for APM?  I've been holding off going to the latest release until I see the sonar will work again.


              • Developer


                     It was a big year for crashes.  Nobody went in last year but this year I think Three planes went in over the day (Philip Rowse's, Michael Oborne's and Greg Fletcher's) and Rob's trad heli went in the previous day during a practice run.  I think 1 copters went in the water but I forget which one.  There was one trad heli that had a bit of a scary high speed crash into a fence (incorrect power set-up caused brown-out) and a multicopter that went to one side of the crowd.

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