[chuck-users] Calculating Motion with Accelerometers

[Inventor-66 at comcast.net]

Regarding methods for caclating motion with accelerometers:  

For the two sensor approach, you subtract the two linear accelerations to get an angular acceleration, and I believe you also divide by the distance between them.  Then you integrate to get angular velocity and integrate again to get angular position (orientation).  To get the X, Y, Z position you just pick one of the sensors and integrate to get velocity then integrate again to get distance.  Now that I think about it, you'd have to remove the gravity vector by taking the high-pass filter of the acceleration with a low cutoff frequency first, or else by subtracting it off.  

The "trick", as i understand it, is to take advantage of the gravity vector so you only need one sensor.  In this case you low-pass-filter the acceleration to get it's "DC" or "near-DC" component, which should give the orientation vector.  Then you high-pass-filter the acceleration to get it's X, Y, Z component and integrate twice to get distance.  It's a touchy sort of trick that requires tweaking and yes, it probably doesn't do so well with sudden motions.  I'm not sure how well either would work, but I'm going to experiment and give it a try.  

Les
(Inventor)