Update default contact model to Soft and remove deprecation warning

src/jaxsim/api/model.py

@@ -247,7 +247,7 @@ def build(
                 The optional name of the model overriding the physics model name.
             contact_model:
                 The contact model to consider.
-                If not specified, a relaxed-constraints rigid contacts model is used.
+                If not specified, a soft contact model is used.
             contact_params: The parameters of the contact model.
             actuation_params: The parameters of the actuation model.
             integrator: The integrator to use for the simulation.
@@ -282,7 +282,7 @@ def build(
         contact_model = (
             contact_model
             if contact_model is not None
-            else jaxsim.rbda.contacts.RelaxedRigidContacts.build()
+            else jaxsim.rbda.contacts.SoftContacts.build()
         )
 
         if contact_params is None:
@@ -2344,9 +2344,6 @@ def update_hw_parameters(
 
     Returns:
         The updated JaxSimModel object with modified hardware parameters.
-
-    Note:
-        This function can be used only with models using Relax-Rigid contact model.
     """
 
     kin_dyn_params: KinDynParameters = model.kin_dyn_parameters

src/jaxsim/rbda/contacts/soft.py

@@ -130,16 +130,12 @@ class SoftContacts(common.ContactModel):
     @classmethod
     def build(
         cls: type[Self],
-        model: js.model.JaxSimModel | None = None,
         **kwargs,
     ) -> Self:
         """
         Create a `SoftContacts` instance with specified parameters.
 
         Args:
-            model:
-                The robot model considered by the contact model.
-                If passed, it is used to estimate good default parameters.
             **kwargs: Additional parameters to pass to the contact model.
 
         Returns:

tests/test_api_model_hw_parametrization.py

@@ -5,6 +5,7 @@
 
 import jaxsim.api as js
 from jaxsim.api.kin_dyn_parameters import HwLinkMetadata, ScalingFactors
+from jaxsim.rbda.contacts import SoftContactsParams
 
 
 def test_update_hw_link_parameters(jaxsim_model_garpez: js.model.JaxSimModel):
@@ -401,6 +402,18 @@ def test_hw_parameters_collision_scaling(
     # Define the scaling factor for the model
     scaling_factor = 5.0
 
+    # Recompute K and D, since the mass is scaled by scaling_factor^3
+    # and the expected static compression of the terrain is approximately
+    # proportional to mass/K and divided by the 4 contact points.
+    K = model.contact_params.K * (scaling_factor**2)
+
+    # Strongly overdamped, to avoid oscillations due to the high mass
+    # and the low penetration allowed.
+    D = 8 * jnp.sqrt(K)
+
+    with model.editable(validate=False) as model:
+        model.contact_params = SoftContactsParams(K=K, D=D)
+
     # Define the nominal radius of the sphere
     nominal_height = model.kin_dyn_parameters.hw_link_metadata.geometry[0, 2]
 
@@ -413,6 +426,9 @@ def test_hw_parameters_collision_scaling(
     # Update the model with the scaling parameters
     updated_model = js.model.update_hw_parameters(model, scaling_parameters)
 
+    # Compute the expected height (nominal radius * scaling factor)
+    expected_height = nominal_height * scaling_factor / 2
+
     # Simulate the box falling under gravity
     data = js.data.JaxSimModelData.build(
         model=updated_model,
@@ -424,7 +440,7 @@ def test_hw_parameters_collision_scaling(
         base_position=jnp.array(
             [
                 *jax.random.uniform(subkey, shape=(2,)),
-                nominal_height * scaling_factor + 0.01,
+                expected_height + 0.05,
             ]
         ),
     )
@@ -440,9 +456,6 @@ def test_hw_parameters_collision_scaling(
     # Get the final height of the box's base
     updated_base_height = data.base_position[2]
 
-    # Compute the expected height (nominal radius * scaling factor)
-    expected_height = nominal_height * scaling_factor / 2
-
     # Assert that the box settles at the expected height
     assert jnp.isclose(
         updated_base_height, expected_height, atol=1e-3

tests/test_automatic_differentiation.py

@@ -297,7 +297,7 @@ def test_ad_soft_contacts(
     model = jaxsim_models_types
 
     with model.editable(validate=False) as model:
-        model.contact_model = jaxsim.rbda.contacts.SoftContacts.build(model=model)
+        model.contact_model = jaxsim.rbda.contacts.SoftContacts.build()
 
     _, subkey1, subkey2, subkey3 = jax.random.split(prng_key, num=4)
     p = jax.random.uniform(subkey1, shape=(3,), minval=-1)

tests/test_simulations.py

@@ -579,6 +579,7 @@ def test_simulation_with_kinematic_constraints_4_bar_linkage(
     data_t0 = js.data.JaxSimModelData.build(
         model=model,
         velocity_representation=VelRepr.Inertial,
+        base_position=jnp.array([0.0, 0.0, 0.10]),
     )
 
     # ====
@@ -607,7 +608,7 @@ def test_simulation_with_kinematic_constraints_4_bar_linkage(
     pos1 = H_frame1[:3, 3]
     pos2 = H_frame2[:3, 3]
     assert pos1 == pytest.approx(
-        pos2, abs=1e-6
+        pos2, abs=1e-5
     ), f"Frame position mismatch. pos1={pos1}, pos2={pos2}, diff={pos1 - pos2}"
 
     # Orientation check