Updates docstring clarifications for joint modeling in 4.5 vs 5.0 (#3869)

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Add docstring clarifications for joint modeling in 4.5 vs 5.0

Replaces this MR - https://github.com/isaac-sim/IsaacLab/pull/3461

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## Type of change

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- Documentation update

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source/isaaclab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.47.4"
+version = "0.47.5"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/isaaclab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.47.5 (2025-10-30)
+~~~~~~~~~~~~~~~~~~~
+
+Changed
+^^^^^^^
+
+* Added docstrings notes to clarify the friction coefficient modeling in Isaac Sim 4.5 and 5.0.
+
+
 0.47.4 (2025-10-30)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/actuators/actuator_cfg.py

@@ -153,10 +153,16 @@ class ActuatorBaseCfg:
     similar to static and Coulomb static friction.
 
     If None, the joint static friction is set to the value from the USD joint prim.
+
+    Note: In Isaac Sim 4.5, this parameter is modeled as a coefficient. In Isaac Sim 5.0 and later,
+    it is modeled as an effort (torque or force).
     """
 
     dynamic_friction: dict[str, float] | float | None = None
     """The dynamic friction coefficient of the joints in the group. Defaults to None.
+
+    Note: In Isaac Sim 4.5, this parameter is modeled as a coefficient. In Isaac Sim 5.0 and later,
+    it is modeled as an effort (torque or force).
     """
 
     viscous_friction: dict[str, float] | float | None = None

source/isaaclab/isaaclab/assets/articulation/articulation_data.py

@@ -196,6 +196,9 @@ class ArticulationData:
     This quantity is configured through the actuator model's :attr:`isaaclab.actuators.ActuatorBaseCfg.friction`
     parameter. If the parameter's value is None, the value parsed from the USD schema, at the time of initialization,
     is used.
+
+    Note: In Isaac Sim 4.5, this parameter is modeled as a coefficient. In Isaac Sim 5.0 and later,
+    it is modeled as an effort (torque or force).
     """
 
     default_joint_dynamic_friction_coeff: torch.Tensor = None
@@ -204,6 +207,9 @@ class ArticulationData:
     This quantity is configured through the actuator model's :attr:`isaaclab.actuators.ActuatorBaseCfg.dynamic_friction`
     parameter. If the parameter's value is None, the value parsed from the USD schema, at the time of initialization,
     is used.
+
+    Note: In Isaac Sim 4.5, this parameter is modeled as a coefficient. In Isaac Sim 5.0 and later,
+    it is modeled as an effort (torque or force).
     """
 
     default_joint_viscous_friction_coeff: torch.Tensor = None
@@ -347,10 +353,18 @@ class ArticulationData:
     """Joint armature provided to the simulation. Shape is (num_instances, num_joints)."""
 
     joint_friction_coeff: torch.Tensor = None
-    """Joint static friction coefficient provided to the simulation. Shape is (num_instances, num_joints)."""
+    """Joint static friction coefficient provided to the simulation. Shape is (num_instances, num_joints).
+
+    Note: In Isaac Sim 4.5, this parameter is modeled as a coefficient. In Isaac Sim 5.0 and later,
+    it is modeled as an effort (torque or force).
+    """
 
     joint_dynamic_friction_coeff: torch.Tensor = None
-    """Joint dynamic friction coefficient provided to the simulation. Shape is (num_instances, num_joints)."""
+    """Joint dynamic friction coefficient provided to the simulation. Shape is (num_instances, num_joints).
+
+    Note: In Isaac Sim 4.5, this parameter is modeled as a coefficient. In Isaac Sim 5.0 and later,
+    it is modeled as an effort (torque or force).
+    """
 
     joint_viscous_friction_coeff: torch.Tensor = None
     """Joint viscous friction coefficient provided to the simulation. Shape is (num_instances, num_joints)."""