If you have a Top Level assembly that contains a sub-assembly that you need to allow motion or movement on, you have to use "Flexible Sub-Assemblies". All you have to do is right-click on the Sub-Assembly from the feature manager tree, and then pick The "Properties" button from the pop up toolbar. After doing this, a small window will pop up and you should see the option of Solve as of "Rigid" or "Flexible". Choose Flexible.
Have more questions? Submit a request