Displacement of a rotating body using 3-axis accelerometer

[Crawl]

Hello all,

I am trying to determine the displacement of a free falling body, which is pivoting about a known location, with experimentally acquired accelerations. I know the initial location and orientations of the accelerometer and its 3-axes. I tested the accelerometer in my office to measure linear displacement in a single direction, with good results. My issue with determining the displacement of the free falling body is that once the body begins to free fall I no longer know the orientation of gravity while it accelerates, and thus I cannot subtract the gravitational acceleration components from the respective recorded accelerations. Fortunately, one axis can be neglected as I am not concerned with the forward/backward movement of the body. My initial thoughts were to take the recorded accelerations and subtract the gravitational components and assume that the remaining accelerations are due to centrifugal acceleration, thus I would be able to solve for the rotational velocity. 

I would appreciate any advice you might have.

Thanks,

Chris

[Hummer1]

If the body is "free falling" not near its terminal velocity, and the accelerometer is attached to it::: Then the accelerations (in all three directions) integrated twice will give you  (orientation), and the position of the center of mass will be given by the s= s0+V0t+1/2gt^2 thing.  are you expecting gyrations caused by external forces...? That is the only thing the accelerometer is going to measure after release...until the body approaches terminal velocity and is no longer being accelerated by g...If the accelerometer is not mounted at the cg, and the object spins...then that is a whole nother kettle of fish...

Hope that helps. 

 (good explanation... http://en.wikipedia.org/wiki/Accelerometer )

Hummer1 

[Crawl]

Hi Hummer1,

My use of "free fall" is poor. I essentially have a body that is sitting on a tilt-table that (very) slowly rotates until the CG passes over the pivot point, then begins to experience rotational acceleration due to gravity.  Once the body begins to accelerate it pivots approximately 75 degrees until impact. My interest is the velocity of the body just prior to impact. The accelerometer was placed at the CG. I know the location of the accelerometer and the orientation of its axes at the instant begins to experience rotational acceleration and the instant just prior to impact. I need to be able to try and account for the direction of gravity and the rotational acceleration, thus I would be able to subtract them from the acceleration readings and assume that the remainder is due to centrifugal acceleration.

Thank you for your time,

Chris