Arducopter 2.8.1 is now in the mission planner and in the downloads area! Remember to do your MP configuration again after loading this code, since it erases your EEPROM and sets it to the new defaults. 

Note: Issues with APM1 user's level feature not working are now resolved.  If you installed 2.8 we highly recommend you upgrade to 2.8.1 as 430 extra bytes of RAM have been freed up which reduces the chance of memory corruption (although we haven't seen any cases of this on the APM2 at least) .

Note #2: this release has not gone out for Traditional Helicopters until they can be tested fully.  Flip and Toy mode have also not been fully tested.

Improvements over 2.7.3:

• Improved ACRO mode (Leonard Hall)
• Improved stability patch to reduce "climb-on-yaw" problem (Leonard, Rob Lefebvre, Randy)
• Rate controller targets moved to body frames (yaw control now works properly when copter is inverted) (Leonard/Randy)
• Less bouncy Stabilize yaw control (Leonard)
• OpticalFlow sensor support for APM2.5 (Randy)
• DMP works again by adding "#define DMP_ENABLED ENABLED" to APM_Config.h You can also log DMP vs DCM to the dataflash by adding "#define SECONDARY_DMP_ENABLED ENABLED" (Randy)
• Watch dog added to shutdown motors if main loop feezes for 2 seconds (Randy)
• Thrust curve added to linearize pwm->thrust. Removes deadzone found above 90% throttle in most ESC/motors (Randy)
• More timing improvements (main loop is now tied to MPU6000s interrupt) (Randy)
• GPS NMEA bug fix (Alexey Kozin)
• Logging improvements (log I terms, dump all settings at head of dataflash log) (Jason)

Bug Fixes / Parameter changes:

• fixed skipping of last waypoint (Jason)
• resolved twitching when no GPS attached (Tridge)
• fixed loss of altitude if alt hold is engaged before first GPS lock (Randy/Jason)
• moved Roll-Pitch I terms from Stabilize controllers to Rate controllers
• TILT_COMPENSATION param tuned for TradHeli (Rob)

Code Cleanup:

• HAL changes for platform portability (Pat Hickey)
• Removed INSTANT_PWM (Randy)

As per usual PIDs are optimised for the 3DR quad with 850 motors and 10" props. If you're using more powerful motors/props and are seeing bad flight behaviour in stabilize, start by turning down Rate Roll P in 25% steps.

Please note that on this release we've moved the Roll and Pitch I terms from the Stabilize controller to the Rate controller. There's some evidence that says this can lead to flips on take-off if you move the roll or pitch sticks around as you take-off so we recommend you leave these sticks in the middle until you're in the air.

Please feel free to report issues you find in the discussion below and/or add them to the issues list.

Thanks and enjoy!

This guide will walk you through the construction for your Arducopter 3DR frame and Power Distribution board.

This Hexa frame is based off the Arducopter 3DR Quadcopter, but includes 2 extra motors for added lift and stability in windy conditions.  This guide will show you how to assemble the kit

Here are two comparison videos of loiter mode for a tricopter fling the latest arducopter 2.6 code, compared to the previous v2.5.5 code.

Thanks to Dean for sharing the videos

Version 2.6 of the ArduCopter code is now available in the AP Mission Planner and in the downloads area!

Updates to MavLink 1.0 means you will need to use "ArdupilotMegaPlanner10.exe" to connect.  If you've updated your mission planner recently you should find this executable in the directory where the mission planner is installed.

The above video is done using a prototype 3dr ublox GPS which seems to have better accuracy than the standard mediatek.

Improvements over 2.5.5 include:
     - MavLink 1.0 support (use with ArdupilotMegaPlanner10.exe) [Tridge, Craig]
     - Stability improvements especially during level hover [Jason]
     - throttle range improvement (higher min and max) [Jason]
     - improved standard Loiter PIDs [Alan, Heino, Jason, Angel]
     - dataflash erase speed up ('+' messages removed but it only takes 6 seconds now) [Tridge]
     - Copter LEDs [Robert Lefebvre]
     - RTL loiter stage target set to home to improve final landing position [Jason]
     - flip & acro improvements [Jason]
     - circle mode target improvement for ground station [Jason]
     - Auto Approach [Adam Rivera / Marco]

Tuning:
PIDs are optimised for the stock Arducopter quad kit with 850 motors and 10" props.  If you're using more powerful motors/props and are seeing bad flight behaviour in stabilize, start by turning down Rate Roll P in 25% steps.

This time we spent some time optimising the loiter PIDs.  Tuning loiter can be tricky so please refer to the discussions which will appear below for more community feedback on what parameters work best.
 
All feedback welcome below.  Enhancement requests and bug reports can be put into the arducopter issues list.  When possible please include logs (tlog and/or dataflash) and tell us whether you're using APM1 or APM2 and what version of the software you're using (presumably 2.6 but tell us anyway!).

Happy flying!

Hardware in the loop simulation for arducopter has been around for a few months already, but it usually requires you to find a quad-copter model for xplane to use yourself, It is not the prettiest model but it gets the job done.  I have attached a decent model of a quad-copter for xplane, along with the parameters (thanks to Jean-Louis) for anyone to easily get started with arducopter hardware in the loop simulation.  Allowing you to test arducopter out in a safe virtual environment.  The file can be downloaded below (Xplane-quad.zip).