Fixes noisy velocities around limits

source/isaaclab/docs/CHANGELOG.rst

@@ -1,6 +1,17 @@
 Changelog
 ---------
 
+0.48.1 (2025-11-10)
+~~~~~~~~~~~~~~~~~~~
+
+Added
+^^^^^
+
+* Added :attr:`~isaaclab.sim.PhysxCfg.enable_external_forces_every_iteration` to enable external forces every position iteration.
+  This can help improve the accuracy of velocity updates. Consider enabling this flag if the velocities generated by the simulation are noisy.
+* Added warning when :attr:`~isaaclab.sim.PhysxCfg.enable_external_forces_every_iteration` is set to False and the solver type is TGS.
+
+
 0.48.0 (2025-11-03)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/sim/simulation_cfg.py

@@ -99,6 +99,19 @@ class PhysxCfg:
         Enabling this flag may lead to incorrect contact forces report from the contact sensor.
     """
 
+    enable_external_forces_every_iteration: bool = False
+    """Enable/disable external forces every position iteration in the TGS solver. Default is False.
+
+    When using the TGS solver (:attr:`solver_type` is 1), this flag allows enabling external forces every solver position iteration.
+    This can help improve the accuracy of velocity updates. Consider enabling this flag if the velocities generated by
+    the simulation are noisy. Increasing the number of velocity iterations, together with this flag, can help improve
+    the accuracy of velocity updates.
+
+    .. note::
+
+        This flag is ignored when using the PGS solver (:attr:`solver_type` is 0).
+    """
+
     enable_enhanced_determinism: bool = False
     """Enable/disable improved determinism at the expense of performance. Defaults to False.
 

source/isaaclab/isaaclab/sim/simulation_context.py

@@ -792,6 +792,19 @@ def _set_additional_physx_params(self):
         physx_prim.CreateAttribute("physxScene:solveArticulationContactLast", Sdf.ValueTypeNames.Bool).Set(
             self.cfg.physx.solve_articulation_contact_last
         )
+        # -- Enable external forces every iteration, helps improve the accuracy of velocity updates.
+
+        if self.cfg.physx.solver_type == 1:
+            if not self.cfg.physx.enable_external_forces_every_iteration:
+                omni.log.warn(
+                    "The `enable_external_forces_every_iteration` parameter in the PhysxCfg is set to False. If you are"
+                    " experiencing noisy velocities, consider enabling this flag. You may need to slightly increase the"
+                    " number of velocity iterations (setting it to 1 or 2 rather than 0), together with this flag, to"
+                    " improve the accuracy of velocity updates."
+                )
+            physx_scene_api.CreateEnableExternalForcesEveryIterationAttr(
+                self.cfg.physx.enable_external_forces_every_iteration
+            )
 
         # -- Gravity
         # note: Isaac sim only takes the "up-axis" as the gravity direction. But physics allows any direction so we