Fixes rigid object's root com velocities timestamp check (#1674)

# Description
The rigid body data properties root_com_vel_w, root_com_pos_w, and
root_com_ang_vel_w currently check the private state field's timestamp
before updating their state. However, the issue lies in the fact that
these COM state properties are incorrectly checking the link state
field's timestamp instead of the COM's own state.

Fixes # (issue)
Replacing root link state with root com state at these properties.

## Type of change
- Bug fix (non-breaking change which fixes an issue)


## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] 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
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

Author: ori-gadot

CONTRIBUTORS.md

@@ -69,6 +69,7 @@ Guidelines for modifications:
 * Muhong Guo
 * Nicola Loi
 * Nuralem Abizov
+* Ori Gadot
 * Oyindamola Omotuyi
 * Özhan Özen
 * Peter Du

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/articulation/articulation_data.py

@@ -547,7 +547,7 @@ def root_link_pos_w(self) -> torch.Tensor:
 
         This quantity is the position of the actor frame of the root rigid body relative to the world.
         """
-        if self._body_com_state_w.timestamp < self._sim_timestamp:
+        if self._root_link_state_w.timestamp < self._sim_timestamp:
             # read data from simulation (pose is of link)
             pose = self._root_physx_view.get_root_transforms()
             return pose[:, :3]
@@ -559,7 +559,7 @@ def root_link_quat_w(self) -> torch.Tensor:
 
         This quantity is the orientation of the actor frame of the root rigid body.
         """
-        if self._body_com_state_w.timestamp < self._sim_timestamp:
+        if self._root_link_state_w.timestamp < self._sim_timestamp:
             # read data from simulation (pose is of link)
             pose = self._root_physx_view.get_root_transforms().clone()
             pose[:, 3:7] = math_utils.convert_quat(pose[:, 3:7], to="wxyz")

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/rigid_object/rigid_object_data.py

@@ -399,7 +399,7 @@ def root_com_vel_w(self) -> torch.Tensor:
 
         This quantity contains the linear and angular velocities of the root rigid body's center of mass frame relative to the world.
         """
-        if self._root_link_state_w.timestamp < self._sim_timestamp:
+        if self._root_com_state_w.timestamp < self._sim_timestamp:
             # read data from simulation
             velocity = self._root_physx_view.get_velocities()
             return velocity
@@ -411,7 +411,7 @@ def root_com_lin_vel_w(self) -> torch.Tensor:
 
         This quantity is the linear velocity of the root rigid body's center of mass frame relative to the world.
         """
-        if self._root_link_state_w.timestamp < self._sim_timestamp:
+        if self._root_com_state_w.timestamp < self._sim_timestamp:
             # read data from simulation
             velocity = self._root_physx_view.get_velocities()
             return velocity[:, 0:3]
@@ -423,7 +423,7 @@ def root_com_ang_vel_w(self) -> torch.Tensor:
 
         This quantity is the angular velocity of the root rigid body's center of mass frame relative to the world.
         """
-        if self._root_link_state_w.timestamp < self._sim_timestamp:
+        if self._root_com_state_w.timestamp < self._sim_timestamp:
             # read data from simulation
             velocity = self._root_physx_view.get_velocities()
             return velocity[:, 3:6]