PhysX Configuration

PhysX Configuration#

PhysX scene-level settings live on PhysxCfg, which replaces the legacy PhysxCfg from Isaac Lab 2.x. Per-actor settings (such as per-articulation iteration counts, contact filtering, or material properties) continue to be authored on the USD schema; see Schema Configuration Classes for the schema-level configuration helpers.

The example below shows a representative PhysxCfg for a contact-rich manipulation task:

from isaaclab.sim import SimulationCfg
from isaaclab_physx.physics import PhysxCfg

physx_cfg = PhysxCfg(
    solver_type=1,                       # TGS
    min_position_iteration_count=8,
    max_position_iteration_count=64,
    min_velocity_iteration_count=1,
    max_velocity_iteration_count=4,
    enable_ccd=False,
    enable_stabilization=True,
    bounce_threshold_velocity=0.2,
    friction_offset_threshold=0.04,
    friction_correlation_distance=0.025,
)

sim_cfg = SimulationCfg(dt=1 / 120, physics=physx_cfg)

Common Parameters#

The following list highlights the parameters that most often need tuning. The full reference lives on PhysxCfg.

Solver Selection#

  • solver_type: 1 for TGS (Temporal Gauss-Seidel, default) or 0 for PGS (Projective Gauss-Seidel). TGS is the recommended default for articulated robots; PGS can be more forgiving on stiff legacy assets.

  • solve_articulation_contact_last: alters the articulation solver order so that dynamic contact is resolved at the end of the solve. Useful for stiff gripping scenarios. Requires Isaac Sim 5.1+.

Solver Iterations#

  • min_position_iteration_count / max_position_iteration_count: clamp range applied to every actor’s individual position-iteration count.

  • min_velocity_iteration_count / max_velocity_iteration_count: clamp range for velocity iterations.

  • enable_external_forces_every_iteration: applies external forces on every TGS position iteration. Reduces noisy velocity updates at additional compute cost; ignored with the PGS solver.

Contact and Stability#

  • enable_ccd: continuous-collision detection for fast-moving bodies.

  • enable_stabilization: extra solver stabilization pass; recommended only when dt is large (< 30 Hz). Corrupts contact-sensor force-magnitude readings — disable it if you rely on the contact sensor for force observations.

  • bounce_threshold_velocity: relative velocity threshold [m/s] above which contacts bounce.

  • friction_offset_threshold: contact point distance [m] at which friction forces are applied.

  • friction_correlation_distance: distance [m] used to merge nearby contacts into a single friction anchor.

GPU Buffer Sizing#

PhysX on the GPU does not dynamically grow scene buffers, so undersized buffers crash or silently drop contacts. The gpu_* fields on PhysxCfg control these capacities. The defaults are tuned for a few-hundred-environment locomotion task; large multi-thousand-environment manipulation tasks usually need to raise:

  • gpu_max_rigid_contact_count

  • gpu_max_rigid_patch_count

  • gpu_found_lost_pairs_capacity

  • gpu_found_lost_aggregate_pairs_capacity

  • gpu_total_aggregate_pairs_capacity

  • gpu_collision_stack_size

  • gpu_heap_capacity

PhysX prints [PhysX] warnings when a buffer is exhausted; treat those as hard failures and re-tune.

See Also#