PhysX Configuration

PhysX Configuration#

PhysX scene-level settings live on PhysxCfg, which replaces the Isaac Lab 2.x PhysxCfg imported from isaaclab.sim. In Isaac Lab 3.0, import PhysxCfg from isaaclab_physx.physics instead. 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=False,
    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. For Isaac Lab 3.0, the supported Isaac Sim versions include this feature; it depends on PhysX schema support introduced in 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 for low-rate simulations, where the simulation timestep dt is larger than about 1 / 30 seconds (below about 30 Hz). This pass can make contact-sensor force magnitudes inaccurate, so keep it disabled 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#