[Joe Johnson]

the problem with using an accelerometer rather than a gyro (i.e. an angular rate sensor -- in the old days, angular rate sensors actually had spinning masses in them that were mounted on a complex mechanism with very good bearings that allowed the spinning mass to keep pointing in the same absolute position regardless of the oreintation of the outside -- this took advantage of the so called gyroscopic effect -- conservation of angular momentum actually but I digress...) is that accelerometers give well... a measurement of acceleration. If the sensor is not accelerating then it can be used as a tilt sensor by measuring the acceleration due to gravity, but if it IS accelerating, life is much more complex -- I think too complex for your system to noodle out.

Gyros -- angular rate sensors -- have there own problems. They too don't give angle -- they give angular rate. But, you can integerate them once to get angle -- this introduces a problem with drift (small errors add up to eventually get the angle estimate off target). Drift can be managed with some creative coding to zero the integration -- when you get to that point, we can talk more.

Joe J.