Adds joint effort observation (#2211)

# Description

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This PR adds in a joint_effort observation that exposes the
`articulation.data.applied_effort`

Fixes # (issue)

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## Type of change

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- New feature (non-breaking change which adds functionality)

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## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
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- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
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---------
Signed-off-by: Kelly Guo <kellyg@nvidia.com>
Signed-off-by: Kelly Guo <kellyguo123@hotmail.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: Kelly Guo <kellyguo123@hotmail.com>

source/isaaclab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.37.0"
+version = "0.38.0"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/isaaclab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.38.0 (2025-04-01)
+~~~~~~~~~~~~~~~~~~
+
+Added
+~~~~~
+
+* Added the :meth:`~isaaclab.env.mdp.observations.joint_effort`
+
+
 0.37.0 (2025-04-01)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/envs/mdp/observations.py

@@ -209,6 +209,23 @@ def joint_vel_rel(env: ManagerBasedEnv, asset_cfg: SceneEntityCfg = SceneEntityC
     return asset.data.joint_vel[:, asset_cfg.joint_ids] - asset.data.default_joint_vel[:, asset_cfg.joint_ids]
 
 
+def joint_effort(env: ManagerBasedEnv, asset_cfg: SceneEntityCfg = SceneEntityCfg("robot")) -> torch.Tensor:
+    """The joint applied effort of the robot.
+
+    NOTE: Only the joints configured in :attr:`asset_cfg.joint_ids` will have their effort returned.
+
+    Args:
+        env: The environment.
+        asset_cfg: The SceneEntity associated with this observation.
+
+    Returns:
+        The joint effort (N or N-m) for joint_names in asset_cfg, shape is [num_env,num_joints].
+    """
+    # extract the used quantities (to enable type-hinting)
+    asset: Articulation = env.scene[asset_cfg.name]
+    return asset.data.applied_torque[:, asset_cfg.joint_ids]
+
+
 """
 Sensors.
 """