Fix duplicated inertial property + free joint issue (#765)

* Fix duplicated inertial property issue

* skip explicit torso action is >1D

* Format

* Don't add freejoints for add_mobile_base

Author: kevin-thankyou-lin

robosuite/models/robots/robot_model.py

@@ -202,9 +202,13 @@ def add_mobile_base(self, mobile_base: MobileBaseModel):
         mount_support = find_elements(
             root=self.worldbody, tags="body", attribs={"name": mobile_base.correct_naming("support")}, return_first=True
         )
-        # Move ALL content from robot0_base to the mobile base support (arms, geoms, inertial)
+        # Move content from robot0_base to the mobile base support (arms, geoms), but skip inertial
+        # elements and freejoints to avoid conflicts and MuJoCo constraints
         for child in all_root_children:
-            mount_support.append(deepcopy(child))
+            # Skip inertial elements to avoid duplicates with mobile base's own inertial
+            # Skip freejoints since they can only be used at top level
+            if child.tag not in ["inertial", "freejoint"]:
+                mount_support.append(deepcopy(child))
             root.remove(child)
         self.merge_assets(mobile_base)
         for one_actuator in mobile_base.actuator: