Mechanica works well on assemblies. Simplification usually requires significant reduction of components in addition to simplification of each component. Symmetrical divisions of model can be done with assembly cuts. I always remove fasteners and then rebuild the connection with something less complex.
You need to assign material properties to each part. If you forget one, Mechanica will usually flag an error but not always.
Connections between parts are critical. Mechanica hates interference fits. If the surfaces of 2 parts mate, mechanical will now automatically weld them together. If 2 parts don't touch they will move independently. This can make model indeterminate if a component is not properly restrained. Many other connections such and springs and bolts can be added to the connection set.
Mechanica does not look at case where deflection causes 2 parts that don’t touch to move into an interference condition. Assumption is that the 2 parts are free to deflect through each other unless you build a connection (usually will give usable results).
On a complex assembly I will usually start with just one or two components that I can restrain and analyze. Everything else is suppressed. Once I get the analysis to run without error I will incrementally add components. Makes errors that prevent the analysis from running easier to find, especially if you run out of memory.
