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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if you are looking at the logs, i agree, but the video tells a different story. what i want to know is why doesnt it descend when flying in reverse? thats gonna drive me crazy!! But in the video you can see the quads go forward on a sloped path, descending. i had to stop their forward motion several times so they wouldnt hit the ground. near the end of both videos i raise the quad up higher, then switch to ALT HOLD, and it just drops down by the time it gets out to the tree. ia m beginning to think i will never figure this out. :(  thanks for responding!!

sorry, the video is a bit long... does it correspond to the log? Meaning are they of the same timelenght? 

One question... this descending you are taling about, at what altitude (more or less) are you starting the experiment (moving forward)?

Yes they both correspond to the logs, what you are viewing is the flight that made that log. I tried 2 different altitudes, start from 8-10 feet, then one from about 15 feet. same result, but it doesnt happen in reverse. i am thinking of just flying my quads in reverse from now on in ALT HOLD :P

hmm I was thinking about ground effect, but 10feet is high enough... Yes reverse your pitch

I haven't looked through all the comments or at the logs but there are a few alt hold issues that we commonly see:

1. slow descent while in Loiter or AltHold caused by the pilot leaving the throttle stick below 40% (i.e. below the deadband).  This sounds silly but it happens a fair bit surprisingly.  You can see if this is the cause by looking at the CTUN message's ThrIn.

2. temporary drop in altitude when the flattening out after high speed forward flight.  This is caused by an aerodynamic effect of the copter.  When the pressure on the top of the copter is higher as it's flying forward and then suddenly released when it leans back.  There's no much you can do about this except try to redesign the aerodynamics of the copter.  If the pressure is balanced between top and bottom of the copter the effect is greatly reduced.

3. barometer drift caused by weather changes.  This will be different on different days though.

at 1. : but if WPAlt is constant... doesn't that mean the throttle is at 50%? PS, I have DAlt in stead of WPAlt with my older version.

thanks Randy!! i can assure you my sticks are at 50%, at least VISUALLY they are. i am Using Turnigy 9XRs Radios for all Quads. ALT HOLD is tricky on all three. wierd thing is, flying in Reverse back to Take Off location there is no drop or descent, it makes a bee line right back?

ThrIn shows at or about 560-600 solid on the value graph. Loiter is rock solid, stays put every time at about 10 feet.

Have you tried re-calibrating the accelerometer?

Looking at the videos the APM seems tilted down slightly at the front end and with the mounting changes it might be worth a try if you haven't already.

Just remember you're making the quad frame level not the APM when you're setting it. I had to make a perfectly level platform to do mine and even then the side positions were a bit hit and miss.

After that, i'm as confused as you are :-s


i have re-calibrated the accelerometer, even re-calibrated the Compass after mounting the new anti-vibration mounts. Mission planner shows it to be level

Why do I's got to get the BROKEN one :P

Could it be as simple as where the Receiver wires are positioned?

All three Quads had the Receiver Wires position on their Left Sides dangling down. i have now spread them apart, one at the rear and one as forward as i can mount it, exposed underneath the body. i have adjusted all the quads receiver wires like this and will test tomorrow.

i realize i am just grasping at straws here but i dont have any other answers unless there is something unique to the Turnigy 9XR running Open TX.

thanks for everyones help, it is appreciated.

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