i create this system with a subsystem (blue part + brown part.... with flexibility). The Cube slide on the long part.
It works fine on assembly design, but when i create mechanism (Mechanical system Design new UI) connexion with parts on subsystems are not added.

So:
- i add submechanism 
- i need to create the new joints (between long part and brown part, and between cube and blue part) ... but i can't add joints

Any ideas ??

Actually, i need to go to Motion Design to create the joint !