Hi Tom,
I was curious if you could tell me any more specific information on the papers you used to write your quaternion and kalman code. You reference that they came from Mahony and Beard, but that hasn't helped much since those guys have written sooo many papers.
Currently I'm testing a quaternion algorithim from Madgwick titled "A efficient orientation filter for IMUs and MARG sensor arrays", and I'm mostly happy with it's implementation, but I've noticed that it has a tendancies to get it's direction vector flipped when in the up-side-down condition too long, so I'm wondering what other people have done to get around this or if I'm just being too nitpicky.
By the way, Thanks, your work has been a big inspiration for me!