I've got an assembly of a gimbal that I'm working on. It has 2 DOF, roll and pitch.
I would like to be able to move/rotate the axes at will in the model by drag-clicking, and I would also like to create subassemblies in order to show mass properties such as mass centres (for each axis).
As far as I am aware, in order to generate a COM feature for a group of components, they need to belong to the same assembly/subassembly. My problem is that as soon as I create a subassembly of, say, the pitch axis components, I can no longer manipulate them in the main assembly.
It sounds like you need to set the subassembly to solve as flexible in top level assembly. Right click on the subassembly and select properties. In the properties dialog set the solve as button to flexible.