Updates Joint Friction Parameters to Isaac Sim 5.0 PhysX APIs (#557)

# Description

Updated Joint Friction Parameters to Isaac Sim 5.0/ PhysX APIs and
exposed joint's viscous_frictions and dynamic_frictions.


## Checklist

- [X] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [X] I have made corresponding changes to the documentation
- [X] My changes generate no new warnings
- [X] I have added tests that prove my fix is effective or that my
feature works
- [X] 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

source/isaaclab/isaaclab/actuators/actuator_base.py

@@ -86,7 +86,13 @@ class ActuatorBase(ABC):
     """The armature of the actuator joints. Shape is (num_envs, num_joints)."""
 
     friction: torch.Tensor
-    """The joint friction of the actuator joints. Shape is (num_envs, num_joints)."""
+    """The joint static friction of the actuator joints. Shape is (num_envs, num_joints)."""
+
+    dynamic_friction: torch.Tensor
+    """The joint dynamic friction of the actuator joints. Shape is (num_envs, num_joints)."""
+
+    viscous_friction: torch.Tensor
+    """The joint viscous friction of the actuator joints. Shape is (num_envs, num_joints)."""
 
     _DEFAULT_MAX_EFFORT_SIM: ClassVar[float] = 1.0e9
     """The default maximum effort for the actuator joints in the simulation. Defaults to 1.0e9.
@@ -106,6 +112,8 @@ class ActuatorBase(ABC):
         damping: torch.Tensor | float = 0.0,
         armature: torch.Tensor | float = 0.0,
         friction: torch.Tensor | float = 0.0,
+        dynamic_friction: torch.Tensor | float = 0.0,
+        viscous_friction: torch.Tensor | float = 0.0,
         effort_limit: torch.Tensor | float = torch.inf,
         velocity_limit: torch.Tensor | float = torch.inf,
     ):
@@ -131,7 +139,11 @@ class ActuatorBase(ABC):
                 If a tensor, then the shape is (num_envs, num_joints).
             armature: The default joint armature. Defaults to 0.0.
                 If a tensor, then the shape is (num_envs, num_joints).
-            friction: The default joint friction. Defaults to 0.0.
+            friction: The default joint static friction. Defaults to 0.0.
+                If a tensor, then the shape is (num_envs, num_joints).
+            dynamic_friction: The default joint dynamic friction. Defaults to 0.0.
+                If a tensor, then the shape is (num_envs, num_joints).
+            viscous_friction: The default joint viscous friction. Defaults to 0.0.
                 If a tensor, then the shape is (num_envs, num_joints).
             effort_limit: The default effort limit. Defaults to infinity.
                 If a tensor, then the shape is (num_envs, num_joints).
@@ -156,6 +168,8 @@ class ActuatorBase(ABC):
         # parse joint armature and friction
         self.armature = self._parse_joint_parameter(self.cfg.armature, armature)
         self.friction = self._parse_joint_parameter(self.cfg.friction, friction)
+        self.dynamic_friction = self._parse_joint_parameter(self.cfg.dynamic_friction, dynamic_friction)
+        self.viscous_friction = self._parse_joint_parameter(self.cfg.viscous_friction, viscous_friction)
         # parse joint limits
         # -- velocity
         self.velocity_limit_sim = self._parse_joint_parameter(self.cfg.velocity_limit_sim, velocity_limit)

source/isaaclab/isaaclab/actuators/actuator_cfg.py

@@ -141,18 +141,26 @@ class ActuatorBaseCfg:
     """
 
     friction: dict[str, float] | float | None = None
-    r"""The friction coefficient of the joints in the group. Defaults to None.
+    r"""The static friction coefficient of the joints in the group. Defaults to None.
 
-    The joint friction is a unitless quantity. It relates the magnitude of the spatial force transmitted
-    from the parent body to the child body to the maximal friction force that may be applied by the solver
+    The joint static friction is a unitless quantity. It relates the magnitude of the spatial force transmitted
+    from the parent body to the child body to the maximal static friction force that may be applied by the solver
     to resist the joint motion.
 
     Mathematically, this means that: :math:`F_{resist} \leq \mu F_{spatial}`, where :math:`F_{resist}`
     is the resisting force applied by the solver and :math:`F_{spatial}` is the spatial force
-    transmitted from the parent body to the child body. The simulated friction effect is therefore
-    similar to static and Coulomb friction.
+    transmitted from the parent body to the child body. The simulated static friction effect is therefore
+    similar to static and Coulomb static friction.
 
-    If None, the joint friction is set to the value from the USD joint prim.
+    If None, the joint static friction is set to the value from the USD joint prim.
+    """
+
+    dynamic_friction: dict[str, float] | float | None = None
+    """The dynamic friction coefficient of the joints in the group. Defaults to None.
+    """
+
+    viscous_friction: dict[str, float] | float | None = None
+    """The viscous friction coefficient of the joints in the group. Defaults to None.
     """
 
 

source/isaaclab/isaaclab/actuators/actuator_pd.py

@@ -379,6 +379,8 @@ class RemotizedPDActuator(DelayedPDActuator):
         damping: torch.Tensor | float = 0.0,
         armature: torch.Tensor | float = 0.0,
         friction: torch.Tensor | float = 0.0,
+        dynamic_friction: torch.Tensor | float = 0.0,
+        viscous_friction: torch.Tensor | float = 0.0,
         effort_limit: torch.Tensor | float = torch.inf,
         velocity_limit: torch.Tensor | float = torch.inf,
     ):
@@ -387,7 +389,19 @@ class RemotizedPDActuator(DelayedPDActuator):
         cfg.velocity_limit = torch.inf
         # call the base method and set default effort_limit and velocity_limit to inf
         super().__init__(
-            cfg, joint_names, joint_ids, num_envs, device, stiffness, damping, armature, friction, torch.inf, torch.inf
+            cfg,
+            joint_names,
+            joint_ids,
+            num_envs,
+            device,
+            stiffness,
+            damping,
+            armature,
+            friction,
+            dynamic_friction,
+            viscous_friction,
+            effort_limit,
+            velocity_limit,
         )
         self._joint_parameter_lookup = torch.tensor(cfg.joint_parameter_lookup, device=device)
         # define remotized joint torque limit

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

@@ -190,13 +190,29 @@ class ArticulationData:
     """
 
     default_joint_friction_coeff: torch.Tensor = None
-    """Default joint friction coefficient of all joints. Shape is (num_instances, num_joints).
+    """Default joint static friction coefficient of all joints. Shape is (num_instances, num_joints).
 
     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.
     """
 
+    default_joint_dynamic_friction_coeff: torch.Tensor = None
+    """Default joint dynamic friction coefficient of all joints. Shape is (num_instances, num_joints).
+
+    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.
+    """
+
+    default_joint_viscous_friction_coeff: torch.Tensor = None
+    """Default joint viscous friction coefficient of all joints. Shape is (num_instances, num_joints).
+
+    This quantity is configured through the actuator model's :attr:`isaaclab.actuators.ActuatorBaseCfg.viscous_friction`
+    parameter. If the parameter's value is None, the value parsed from the USD schema, at the time of initialization,
+    is used.
+    """
+
     default_joint_pos_limits: torch.Tensor = None
     """Default joint position limits of all joints. Shape is (num_instances, num_joints, 2).
 
@@ -330,7 +346,13 @@ class ArticulationData:
     """Joint armature provided to the simulation. Shape is (num_instances, num_joints)."""
 
     joint_friction_coeff: torch.Tensor = None
-    """Joint 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)."""
+
+    joint_dynamic_friction_coeff: torch.Tensor = None
+    """Joint dynamic friction coefficient provided to the simulation. Shape is (num_instances, num_joints)."""
+
+    joint_viscous_friction_coeff: torch.Tensor = None
+    """Joint viscous friction coefficient provided to the simulation. Shape is (num_instances, num_joints)."""
 
     joint_pos_limits: torch.Tensor = None
     """Joint position limits provided to the simulation. Shape is (num_instances, num_joints, 2).

source/isaaclab/test/assets/test_articulation.py

@@ -1899,5 +1899,44 @@ def test_spatial_tendons(sim, num_articulations, device):
         articulation.update(sim.cfg.dt)
 
 
+@pytest.mark.parametrize("add_ground_plane", [True])
+@pytest.mark.parametrize("num_articulations", [1, 2])
+@pytest.mark.parametrize("device", ["cuda:0", "cpu"])
+def test_write_joint_frictions_to_sim(sim, num_articulations, device, add_ground_plane):
+    """Test applying of joint position target functions correctly for a robotic arm."""
+    articulation_cfg = generate_articulation_cfg(articulation_type="panda")
+    articulation, _ = generate_articulation(
+        articulation_cfg=articulation_cfg, num_articulations=num_articulations, device=device
+    )
+
+    # Play the simulator
+    sim.reset()
+
+    for _ in range(100):
+        # perform step
+        sim.step()
+        # update buffers
+        articulation.update(sim.cfg.dt)
+
+    # apply action to the articulation
+    dynamic_friction = torch.rand(num_articulations, articulation.num_joints, device=device)
+    viscous_friction = torch.rand(num_articulations, articulation.num_joints, device=device)
+    friction = torch.rand(num_articulations, articulation.num_joints, device=device)
+    articulation.write_joint_dynamic_friction_coefficient_to_sim(dynamic_friction)
+    articulation.write_joint_viscous_friction_coefficient_to_sim(viscous_friction)
+    articulation.write_joint_friction_coefficient_to_sim(friction)
+    articulation.write_data_to_sim()
+
+    for _ in range(100):
+        # perform step
+        sim.step()
+        # update buffers
+        articulation.update(sim.cfg.dt)
+
+    assert torch.allclose(articulation.data.joint_dynamic_friction_coeff, dynamic_friction)
+    assert torch.allclose(articulation.data.joint_viscous_friction_coeff, viscous_friction)
+    assert torch.allclose(articulation.data.joint_friction_coeff, friction)
+
+
 if __name__ == "__main__":
     pytest.main([__file__, "-v", "--maxfail=1"])