I would like to simulate a machine with unbalance motors to see stresses and so on.
The machine stands on rubber isolator so I can't set that surface to fixed...
I have no idea how to set it up, any idea?
You need to know the spring rate of the rubber or the material properties and the design. If you know the spring rate, you can use any combination of "Setup > Constraints > General Constraints", "1D Spring Supports", and "3D Spring Supports". If you know the material propeties, you can model the rubber and fix the other end appropriately.
If you do not know anything about the rubber, then it is hard to include it in the analysis.
Simulation Mechanical user since Dec 1997