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

# Description

<!--
Thank you for your interest in sending a pull request. Please make sure
to check the contribution guidelines.

Link:
https://isaac-sim.github.io/IsaacLab/main/source/refs/contributing.html

💡 Please try to keep PRs small and focused. Large PRs are harder to
review and merge.
-->

Add docstring clarifications for joint modeling in 4.5 vs 5.0

Replaces this MR - #3461

<!-- As a practice, it is recommended to open an issue to have
discussions on the proposed pull request.
This makes it easier for the community to keep track of what is being
developed or added, and if a given feature
is demanded by more than one party. -->

## Type of change

<!-- As you go through the list, delete the ones that are not
applicable. -->

- Documentation update

## Screenshots

Please attach before and after screenshots of the change if applicable.

<!--
Example:

| Before | After |
| ------ | ----- |
| _gif/png before_ | _gif/png after_ |

To upload images to a PR -- simply drag and drop an image while in edit
mode and it should upload the image directly. You can then paste that
source into the above before/after sections.
-->

## Checklist

- [ ] I have read and understood the [contribution
guidelines](https://isaac-sim.github.io/IsaacLab/main/source/refs/contributing.html)
- [ ] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
As you go through the checklist above, you can mark something as done by
putting an x character in it

For example,
- [x] I have done this task
- [ ] I have not done this task
-->

Author: matthewtrepte

source/isaaclab/config/extension.toml

@@ -1,7 +1,7 @@
 [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

@@ -1,6 +1,15 @@
 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 @@ def update(self, dt: float):
     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 @@ def update(self, dt: float):
     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 @@ def update(self, dt: float):
     """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)."""