accelerometer g force/vectors

Hello,

I was wondering is someone can help me please with the mathematics of forces/vectors and acceleration. Now I realize that I have a good deal to learn on the subject but as I am starting out on this venture the challenge is find the right reference,. Hence I need more than just a little help; so to the problem.

I have an accelerometer that I can read the x, y, z g forces from, and I have record two sets of data that can be found below. The first set is the static, and the second set are reading taken when the device was accelerating. The device is tiled over at 45 degrees around the y axis thus the orientation of the device is x=45, y=0, z=45 for both sets of measurements.

I can calculate the total g force from the device thus:

sqrt(x*x+y*y+z*z) and the angle of an axis thus by the cos-1 thus 0.7 g = 45 degrees.

Now this works for the static case, but does not work for the dynamic (accelerating) case. I have tried to scale the x, y, z g forces by the total g force but the cos-1 produces an incorrect result as the orientation of the device has not changed..

Can you help?

Many thanks in advance IMK

Static Data acceleromter at rest

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X | Y | Z |

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45 | 0 | 45 | Device Orientation

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0.7 | 0.0 | 0.7 | x,y,z g's. Thus sqrt(x*x+y*y+z*z)=1.0 (Scale=1/1=1)

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0.7*1 | 0.0*1 | 0.7*1 | Scale each g value thus

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0.7 | 0.0 | 0.7 | cos-1 eg acos( 0.7 ) = 45

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45 | 0 | 45 | Degress

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Dynamic Data acceleromter moved horizontally

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X | Y | Z |

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45 | 0 | 45 | Device Orientation

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1.2 | 0.0 | 0.45 | x,y,z g's. Thus sqrt(x*x+y*y+z*z)=1.28 (Scale=1/1=0.78)

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1.2*.78| 0*0.78|.45*.78| Scale each g value thus

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0.93 | 0.0 | 0.35 | cos-1 eg acos( n ) = are incorrect ?

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21 | 0 | 69 | Degress

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As the orientation of the device has not changed these angles should be:

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45 | 0 | 45 |

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