Hello everyone!
Just got my board manufactured a few weeks ago, so it's time to post a little description of my ongoing project here, so this is it:

Here is what's embedded onboard:

Processing elements:
- CPU: Microchip dsPIC33F256 at 40Mhz, allowing a processing power of 40MIPS and with 12bit resolution ADC for better accuracy in measuring the values of analog sensors.
- FPGA: Will take care of converting PWM data from receiver (12 channels supported) and reencode PWM data to servos (12 channels). This way the board is able to support any receiver available, including thoses using PCM encoding.

Sensors:
- 3 axis accelerometer with 4 sensitivity scale (from Freescale)
- 1 axis gyro on the Z axis, with a 150°/s max sensitivity, and integrated temperature sensor
- 2 axis geomagnetic compas
- Barometric pressure sensor
- 2 hall effect sensor, for rotor ans motor RPM monitoring
- Thermocouple, for engine temp. sensing
- Electric field imaging device with 3 antennas (one for monitoring fuel level)
- Ultrasonic range finder, up to 8 meter (driven by the FPGA)
- 12 channels WAAS GPS receiver, outputing NMEA or proprietary 5Hz protocol

Communication:
- Embedded audio/video transmitter with 2km range
- Modem (integrated in FPGA) for sending live flight data to ground on the audio channel of the transmitter
- Orders can be sent by dedicating one of the remote control channel

Imaging:
- An embedded sony 7.2Mpix still digital camera with video mode. All controls (zoom, focus, shooting mode, trigger) are operated remotely
- Tilt rig from 0 to 90°, for pointing the camera remotely

Misc:
- An embedded 4 elements LiPO battery charger, and intelligent battery fuel gauge embedded in the battery pack
- Pushbuttons, buzzer and LEDs
- Serial port for ground debug

The board is still in testing stage, and most of the passive components need to be ordered, but it is comming. The real challenge will come with programming!

On this aspect, I have only 4DOF on the inertial unit...
this raise the same questions that Harrison Jones have in his dual axis accelerometer project, as far as how much will be enough for hovering. I still have an easy way to upgrade my board to 6DOF if I need it but I would rather avoid it if possible.

I understand that gyro on the yaw axis is absolutely mandatory to keep the heading (plus the compas will help), but any displacement of the helicopter should generate an acceleration. I understand then that there's lot of issues as to what created the acceleration and how to process it, as well as drift due to noise and the minute measurements necessary. However, I don't understand how gyros can help if the helicopter is in constant velocity translation: the accelerometer won't register the displacement of course, but the gyros shouldn't as well as there's no angular velocity involved in translation.