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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How is the sonar on this version? On my 3.0.1 it isn't great but other than that I have a perfect flying machine.

I just checked your username and it is working fine.  You have to make at least one moderated post before your account is fully activated

Can we Add an Explanation of Thr_IN THR_OUT to the Log Diagnoses Wiki ? I forgot what it means When ThrIn Is above ThrOut. am i under powered? How do you correct that? Change THR_MID? i dont think this counts as  a support question on firmware 3.1, thats why i asked it here? thanks in advance

Hi Gary, That is what I used. I checked another thread that had an attachment. That attachment was a zip file (.zip extension). I was wondering if my file wasn't showing up because it has a .log extension.

Randy, two weeks ago I asked for help because I was having a message "bad compass health" using an external mag. Ended up I changed the external mag for another one, same type, and problem is gone. No more error messages. Maybe i just had bad luck with that first external mag. 

APM now its working pretty good. No more heading problems, loiter is perfect (outperform my naza at strong wind), no more TBE, no more yaw problems. You guys did a pretty damn good job. Thank you.

Only problem i am facing now (last one) is when the quad hit the waypoint it drop from sky and when it almost hit the ground it goes up fast back  to the right altitude and go to the next waypoint. It is behaving like that when reach every waypoint. Could be a problem related to an uncovered barometer?

My best regards,



Hi John,

Sonar on 3.1 is not great either.  Have a look here:

Thanks Andre something to keep in mind i guess. After reading that it could be "gain" issues I might lower even more from 0.8 to maybe a 0.5. The copter does great above sonar height and I mean its perfect i could be happier I just have to always not to myself not to hit loiter alt hold in sonar range but I will try it and see what happens. Maybe i need to put a mattress under it lol... 

ArduCopter 3.1 Traditional heli will destroy your heli if you manage to fly unarmed in stab mode and switch to AltHold. As soon you switch to AltHold the collective pitch will go to the minimum position, and drives the heli like a rocket into the ground.
It happened to me. The heli flew like a dream in stab mode but unarmed until I tried AltHold.
You are able to get collective pitch if unarmed, so you not realising that the APM has, after a while disarmed again. ArduCopter 2.7 allowed NO collective pitch if not armed.

Hello,Randy!I've flied the AC3.1hexa for many times.In loiter mode,I tried takeoff and land,when i push the throttle slowly,it works properly,but when i push the throttle fast,it will takeoff suddenly sometimes,and the throttle is lower than the mid.How it happens

I faced the same problem when giving a yaw input in any mode using the baro...

It went away after covering the baro with a piece of foam.

Now it's perfect.

Great job done on this release !!!

makes sense your explanation to me, wondering thy the logic was changed.

i am at the point to try the AC31 on my 450 class heli. good to know this before trying.

испытания прошли успешно, благодарю - the tests were successful, thank

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