Hi fellow people,

Some time ago I got interested into Segway and thought of reproducing one. I made my own:

Video here :
http://www.youtube.com/watch?v=CTeuohFkMlg

You can see an ugly arm which acts as a floor riding sensor(a free arm which is connected to a potentiometer to act as an angle sensor)
Originally I Intended to use an accelerometer (ADXL202 two axis accelerometer) as a tilt sensor to read the angle of the robot to the ground. Since they measure the earth gravity, if rotated in an axis they will read differently which lets them to function as a neat absolute tilt sensor.
However they are intended to measure acceleration, and therefore can only be used as tilt sensors with acceleration introduced on them. Otherwise the acceleration will ruin the tilt measurement.
I've been told with the use of another one I can measure the acceleration and decrease it from the reading of the original one letting me end up with the angle at the end. I've told that this can be done barely with op-amps! Recently, I faced with another project report in which I think some one had used the same technique. I have taken the image circuit from here and you see it below:


I am not so intelligent when it comes to physics and mathematics mixed with analog circuits. Does anyone has any idea about this circuit and what it is doing ? Is this what I am guessing ?
Anyother ideas about how to measure angles ?

back from long absence,
Farshid