Ronf,
Thank you for that link, good price on that one! But it is a acceleromter so it won't work (on it's own) for sensing tilt in a dynamic enviroment. I have the sensor hardware covered, accelerometer and gyro, it's how to combine the two readings into one stable tilt angle that is the problem/exercise.

Vacpress,
Thank you! The Kalman code that I posted IS from the NV article. They in turn probably got it from the AutoPilot project on Sourcforge, it's written by Trammell Hudson at Rotomotion. They supposedly used to make low cost IMU's but seems to have moved on to bigger high dollar things.

It was indeed the nBot that got me started on this. I have since looked at everything I could find on the net.

What you say about learning the math is what I'm trying to do here ;-) If someone already had ported it PBP it would be easier (relative term) to understand it than from the C code from Rotomotion.

It seems that some get away by just integrating the rate gyro signal but that doesn't work to good with my sensor, which is the ADXRS150 that I got from www.sparkfun.com

I took the same route as the nBot creator and started by balancing a pole on top of a stable (non tilting) platform. So I have the PID code for driving the motors once I have stable tilt angle feeding the PID regulator.

This is a complex project, motivation and time comes and goes but i WILL make it work, someday.... ;-)

Thanks guys!
/Henrik Olsson.