Cosmos Rocker Arm Pivot Constraints

[rjwoods77]

I am doing a rocker arm in cosmos and have everything all set except for the pivot constraint. I am getting results that dont seems right and I suspect it to be my contraints (fixed all). I have a pure rotation rocker arm(in-plane pullrod setup). How should I lock the frame pivot down? I was thinking you should leave the rotation axis free and lock the others. I am asking before I do it again because I have only one shot access for now until we get our student package and want to make the most of my time.

[rjwoods77]

I am doing a rocker arm in cosmos and have everything all set except for the pivot constraint. I am getting results that dont seems right and I suspect it to be my contraints (fixed all). I have a pure rotation rocker arm(in-plane pullrod setup). How should I lock the frame pivot down? I was thinking you should leave the rotation axis free and lock the others. I am asking before I do it again because I have only one shot access for now until we get our student package and want to make the most of my time.

[DH]

You will definitely not want to constrain the rocker against rotation. In Mechanica I would use a cylindrical coordinate system located at the pivot to constrain the pivot bearing surfaces in r and z, and leave theta unconstrained. I would then apply a load at the pullrod interface and a constraint in z and theta at the damper interface. Leaving the damper interface free in r allows for proper deformation.

I'm not familiar with Cosmos, but you should be able to do this (and much more I hear).

Cheers,

Dan

[billywight]

Just model it as it is in real life - look at the problem and determine what needs to rotate and what needs to be fixed (for every pivot, bolt, etc look at the DOF's and determine what needs to be fixed).

Instead of using a fixed constraint on Cosmos, look at the other restraint types, particularly the one for a cylindrical surface. These make life easy as you don't have to set up extra coordinate systems.