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# How to determine joint axis of operation?

## How to determine joint axis of operation?

(OP)
To measure the forces on the bearings inside a MacPherson shock absorber (strut), I built a simple test model to test the behavior. In the first model I placed the strut vertically (lower and upper mounting point exactly above each other), so the axis of operation of the joints (bearings) were straightforward. R1: [1 0 0] R2: [0 1 0] R3: [0 0 1] P1: [0 0 1]

This model seems to work according to expectations. The normal forces on the bearings matched the ones determined by hand calculations.

In a second model, I placed the strut according to the real coordinates, so it will not be completely vertical, but under a small angle.

The question is now, what should be the axes of operation?

Vertical test model:
http://www.2shared.com/file/2EoCm68I/test_shockabsorber_MB.html

Inclined test model (also uploaded to this forum):
http://www.2shared.com/file/Eskbij2r/test_shockabsorber_MB_inclined.html

Picture of the test model:
http://imageshack.us/photo/my-images/84/testmodel.png/

Drawing of shock absorber:
http://imageshack.us/photo/my-images/10/shockabsorber.png/

### RE: How to determine joint axis of operation?

(OP)
Nobody knows how to determine these axes of operation?

### RE: How to determine joint axis of operation?

(OP)
The orientation of the base is just [0 0 0]  (Euler x-y-z) with respect to the world coordinate system.
The world coordinate system is defined as follows, when looking to the rear view of a vehicle:
x -> inside the screen/paper
y -> horizontally to the left
z -> vertically upwards

Or isn't this what you mean?

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