This project contains the autopilot and on-board computer firmware
code for a quad- / tri- / dual copter I'm making mainly for aerial
photography for OpenStreetMap.  The flight computer is based on
an Arduino Duemilanove board with several sensors (see below) but
the code is mostly generic.  The most tricky part is definitely the
AHRS maths which is very platform independent.

There are other projects that implement an Arduino-based or AVR-based
autopilot, namely there are at least these: Ardupilot/Arducopter,
Openpilot, mikrokopter.de and to some extent the kkmulticopter
firmware.  Arducopter/Ardupilot and Openpilot implement the real
thing: a kalman filter in floating point with matrices and/or
quaternions.  This is a bit of overkill for a real-time process on
an Atmega processor.  microcopter.de is quite cool but code is a
little chaotic, in German, and not freely-licensed.  It's also
very much adapted to a single hardware platform.  All these projects
also have mainly ms Windows support for the ground station code and
only some partial or unofficial/unsupported unix/linux code.
kkmulticopter, while it has a really simple and fast code, is too
simplified and uses mainly only a very precise gyro, while my
platform can make use of other sensors, but its gyros are far from
perfect.

The hardware was selected to use the cheapest usable parts to make
the whole project easily reproducible.

The current hardware confiuration in my device looks something like:

 ,-------.
 |Arduino| >--- 3.3V ---...
 |  Due  |
 | -mila |   5V DC in from uBEC to Vcc
 | -nove | <--- 1x --,                     ,-----------< 11V battery
 | ,-----|            >-- 4x --- 4x 30A ESC
 | |     | >--- 4x --'                     '-- 4x -----> 4x brushless motor
 | |  A  |   4x PPM signal from digital OUT
 | |  t  |
 | |  M  | <----- Analog -----< LPR530AL 2-axis gyro <------ 3.3V ---..
 | |  e  |
 | |  g  | <----- I^2C -------< CMPS09 3-axis Mag&Accel <--- 3.3V ---..
 | |  a  |
 | |  3  | <--- PPM @ 4x or 1x digital IN ---< E-sky stock radio rx <-- 5V --..
 | |  2  |
 | |  8  | <--- UART ---< LS20126 GPS <-- 5V ---..
 | |  p  | <--- UART ---> Xbee Pro modem @ 868 MHz <--- 5V ---..
 | |     |
 `-^-----' >--- UART ---> onboard FT232 <--- USB ---> PC
   <------------ 5V DC in -----'