newton-physics · jumyungc · Feb 27, 2026 · Mar 3, 2026 · Mar 3, 2026 · Mar 3, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -42,6 +42,8 @@
 - Add `ViewerGL.log_scalar()` for live scalar time-series plots in the viewer
 - Add `deterministic` flag to `CollisionPipeline` and `NarrowPhase` for GPU-thread-scheduling-independent contact ordering via radix sort and deterministic fingerprint tiebreaking in contact reduction
 - Add `ViewerBase.log_arrows()` for arrow rendering (wide line + arrowhead) in the GL viewer with a dedicated geometry shader
+- Add `SolverVBD.set_joint_constraint_mode()` and `SolverVBD.JointSlot` for runtime hard/soft constraint toggling per joint
+- Add `rigid_contact_hard`, `rigid_contact_history`, `rigid_avbd_contact_alpha`, `rigid_avbd_joint_alpha` params to `SolverVBD` for augmented-Lagrangian contact and joint control
 
 ### Changed
 
@@ -73,6 +75,8 @@
 - Pin `mujoco` and `mujoco-warp` dependencies to `~=3.6.0`
 - Update default environment map texture in GL viewer (source: https://polyhaven.com/a/brown_photostudio_02)
 - Increase conveyor rail roughness in `example_basic_conveyor` to reduce mirror-like reflections
+- Reduce default `stretch_stiffness` from `1.0e9` to `1.0e4` in `add_rod()` and `add_rod_graph()`
+- VBD solver uses augmented-Lagrangian hard constraints for body-body contacts by default (`rigid_contact_hard=True`)
 
 ### Deprecated
 
@@ -90,6 +94,7 @@
 - Deprecate `ModelBuilder.add_shape_ellipsoid()` parameters `a`, `b`, `c` in favor of `rx`, `ry`, `rz`
 - Deprecate passing a `Gaussian` as the second positional argument to `ModelBuilder.add_shape_gaussian()`; use the `gaussian=` keyword argument instead
 - Deprecate `SensorTiledCamera.utils.assign_random_colors_per_world()` and `assign_random_colors_per_shape()` in favor of per-shape colors via `ModelBuilder.add_shape_*(color=...)`
+- Deprecate `rigid_enable_dahl_friction` in `SolverVBD`; Dahl friction is now auto-detected from model attributes (`model.vbd.dahl_eps_max` / `model.vbd.dahl_tau`)
 
 ### Removed
 

diff --git a/docs/images/examples/example_cable_pile.jpg b/docs/images/examples/example_cable_pile.jpg
diff --git a/newton/_src/sim/builder.py b/newton/_src/sim/builder.py
@@ -4213,7 +4213,7 @@ def add_joint_cable(
 
         """
         # Linear DOF (stretch)
-        se_ke = 1.0e9 if stretch_stiffness is None else stretch_stiffness
+        se_ke = 1.0e4 if stretch_stiffness is None else stretch_stiffness
         se_kd = 0.0 if stretch_damping is None else stretch_damping
         ax_lin = ModelBuilder.JointDofConfig(target_ke=se_ke, target_kd=se_kd)
 
@@ -6421,7 +6421,7 @@ def add_rod(
             cfg = self.default_shape_cfg
 
         # Stretch defaults: high stiffness to keep neighboring capsules tightly coupled
-        stretch_stiffness = 1.0e9 if stretch_stiffness is None else stretch_stiffness
+        stretch_stiffness = 1.0e4 if stretch_stiffness is None else stretch_stiffness
         stretch_damping = 0.0 if stretch_damping is None else stretch_damping
 
         # Bend defaults: 0.0 (users must explicitly set for bending resistance)
@@ -6599,7 +6599,7 @@ def add_rod_graph(
             cfg = self.default_shape_cfg
 
         # Stretch defaults: high stiffness to keep neighboring capsules tightly coupled
-        stretch_stiffness = 1.0e9 if stretch_stiffness is None else stretch_stiffness
+        stretch_stiffness = 1.0e4 if stretch_stiffness is None else stretch_stiffness
         stretch_damping = 0.0 if stretch_damping is None else stretch_damping
 
         # Bend defaults: 0.0 (users must explicitly set for bending resistance)

diff --git a/newton/_src/solvers/vbd/particle_vbd_kernels.py b/newton/_src/solvers/vbd/particle_vbd_kernels.py
@@ -16,7 +16,7 @@
 import warp as wp
 
 from newton._src.math import orthonormal_basis
-from newton._src.solvers.vbd.rigid_vbd_kernels import evaluate_body_particle_contact
+from newton._src.solvers.vbd.rigid_vbd_kernels import _eval_body_particle_contact, evaluate_body_particle_contact
 
 from ...geometry import ParticleFlags
 from ...geometry.kernels import triangle_closest_point
@@ -2439,7 +2439,7 @@ def accumulate_contact_force_and_hessian_no_self_contact(
             contact_kd = body_particle_contact_material_kd[t_id]
             contact_mu = body_particle_contact_material_mu[t_id]
 
-            body_contact_force, body_contact_hessian = evaluate_body_particle_contact(
+            body_contact_force, body_contact_hessian = _eval_body_particle_contact(
                 particle_idx,
                 pos[particle_idx],
                 pos_anchor[particle_idx],
@@ -2449,7 +2449,6 @@ def accumulate_contact_force_and_hessian_no_self_contact(
                 contact_mu,
                 friction_epsilon,
                 particle_radius,
-                shape_material_mu,
                 shape_body,
                 body_q,
                 body_q_prev,
@@ -2940,7 +2939,7 @@ def accumulate_particle_body_contact_force_and_hessian(
             contact_kd = body_particle_contact_material_kd[t_id]
             contact_mu = body_particle_contact_material_mu[t_id]
 
-            body_contact_force, body_contact_hessian = evaluate_body_particle_contact(
+            body_contact_force, body_contact_hessian = _eval_body_particle_contact(
                 particle_idx,
                 pos[particle_idx],
                 pos_anchor[particle_idx],
@@ -2950,7 +2949,6 @@ def accumulate_particle_body_contact_force_and_hessian(
                 contact_mu,
                 friction_epsilon,
                 particle_radius,
-                shape_material_mu,
                 shape_body,
                 body_q,
                 body_q_prev,