Interpretation of dynamic simulation results.

[Bill Swann]

In the attached image, the position and velocity of the crank are graphed. I understand the spike in the velocity curve - it is the speed change when the piston goes thru top dead center. What I do not understand is how to change the start angle on the position curve. It is listed as -138 degrees in the data set. How do I change the initial conditions? The spring acts not as a spring, but as a damper / disipative force.
Thanks

[JDMather]

>how to change the start angle on the position curve
If I follow I think you need to edit the Properties of the Crank Revolution Joint - Initial Position.

Also I think I would display those two graphs separately.

Can you post what you have so far so that I can experiment with the assembly?

[jean-yves.machillot]

Hi Bill,
I think you use the automatic translation from constraints to joints then you have a certain initial position in joints. If you want to obtain 0.0, you can either change the initial position but the mechanism moves also or you can add an offset to the initial position (right click in the field and check "Set Offset", look at the attached image). With this feature, the initial position equals 0.0 and the mechanism does not move. Of course, the position starts to 0.0 in the Output Grapher.
The spike in the velocity curve means the crankshaft is quickly accelerated and slowed down, what is the effect you want and how do you model it ?
Thanks
JYves