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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        • Your understanding of THR_MID is your problem, then. Your stick must be centered regardless of the THR_MID setting. The THR_MID setting applies a throttle curve during direct throttle control modes. Graph CTUN.WPAlt and CTUN.ThrIn

          Your vibration levels are also awfully high.

          • Thanks for Answering Jon, but according to the APM wiki page, i am well within vibration limits unless that page is out dated? i have ordered an anti vibration unit, because i suspect the wiki is not as up to date for the newer firmware. 

            that aside, i am willing to wait for the 3.2 Firmware, which i thought was releasing end of april, so i can just take off in ALT HOLD/LOITER like i do in stabilize.

            since the THR_MID range is 300-700 it indicates to me that a mid Throttle can be with in that range. what confuses me is why THR_MID is not the governing point for all modes, not every model of quad takes off at the exact same point, there are always slight variations aircraft to aircraft.

            again thanks for your answer it is much appreciated.

            • If you set up the THR_MID correctly, your copter should hover at the mid stick and when you switch between the stabilize and alt-hold/loiter, copter shouldn't ascend or descend significantly.

              I kind of gathered what Jonathan said above from your explanation. You might be a little vague about the THR_MID setting. If your copter is hovering below mid-stick and say that is about 40% of the throttle range, then you enter 400 as THR_MID and when you fly the next time, you need to push the stick to mid point to achieve the same result because the APM applies a throttle curve where the 40% throttle output is NOT achieved with 40% throttle input. It is now achieved when the throttle is at mi-stick (which is 50%). So it sets a throttle curve for you.

              If this is set correctly, your copter should not go up/down during flight mode changes. But you need to set the THR_MID precisely. It is not always 300,400,600 etc. Sometimes it is 350, 375. You need to calculate that based on the number of notches on your throttle stick and where exactly your hover point is... 

              • ALEX!!! that was the BEST explanation i ever had on THR_MID, and it is most appreciated.  

                i knew i was missing part of the info i just didnt know what that was. thanks SO much.

                i will go back thru gauging THR_MID. this helped TREMENDOUSLY in understanding the Purpose of THR_MID, they should copy your comment into the WIKI :)

                  • Developer

                    Exactly, many things are documented, take time to read the new wiki! ;-)
                    However personally I prefer to have linear throttle curve, i don't change that parameter.

                • Developer

                  Check the throttle value in the Planner via telemetry when you are in perfect hovering, then insert this value in the THR_MID parameters, that's all.

                  • Where exactly is this NEW WIKI? i just want to know if i am understanding you correctly, Launch the Quad, get a stable Hover,, Look in Mission Planner and look at the Way Point Planner? or am i looking at the status Tab in mission Planner?

                    thanks again

                  • is this an undocumented feature? :P seriously, do i have to enable something to see this value in planner or is it already being sent by telemetry & already visible? i never heard of this before? thanks for your help Marco.

                • Thank you. Part of the credit should go to Jonathan Challinger. He caught your misunderstanding first and I wrapped it up:)

                  The problem with the Wiki is that so many features being added and many things being changed constantly so it is getting very difficult to keep the Wiki up-to-date. I guess there should be someone whose sole duty is to keep the Wiki up-to-date:)


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