YAML: simulationclassSimulationConfig

Simulation

Declares the simulation backend and runtime parameters. stereotype selects the engine; UniSimFactory instantiates the corresponding UniSim subclass.

sourcefastsim/configs/simulation_cfg.py

Top-level fields IsaacLab Backend (stereotype: isaaclab)MuJoCo Backend (stereotype: mujoco)PyBullet Backend (stereotype: pybullet)Example Common errors

Top-level Fields5

Field	Type	Required	Default	Description / Constraints
`stereotype`	string	required	—	Simulation backend identifier (isaaclab / mujoco / pybullet); must be registered in the UniSim registry ⚠Run fastsim show-registry to list available values; custom backends require scan_project
`dt`	float	required	—	Physics timestep in seconds; typical value 0.0166667 (60 Hz) ⚠Must be > 0
`initialize_steps`	int	optional	`60`	Initialization steps after reset to let the physics world stabilize before the task begins ⚠Must be >= 0
`num_envs`	int	optional	`1`	Number of parallel environments (GPU parallel simulation); 1 = single environment ⚠Must be >= 1
`env_spacing`	float	optional	`2.5`	Spacing between parallel environments in meters; effective when num_envs > 1 ⚠Must be > 0

IsaacLab Backend (stereotype: isaaclab)

When stereotype is isaaclab, the config class is IsaacLabConfig, extending the common fields with the following parameters and three nested config objects.

classIsaacLabConfigstereotypeisaaclabfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`device`	string	required	`cuda:0`	Compute device ⚠cpu or cuda:<index> (e.g. cuda:0, cuda:1)
`render_interval`	int	required	`1`	Render one frame every N physics steps ⚠Must be >= 1
`gravity`	tuple[3]	required	`(0.0, 0.0, -9.81)`	Gravity vector (x, y, z) in m/s²
`physics_prim_path`	string	required	`/physicsScene`	Physics scene prim path ⚠Must start with /
`enable_scene_query_support`	bool	required	`false`	Enable scene query support (ray casting, etc.)
`use_fabric`	bool	required	`true`	Use Fabric data interface for accelerated data access
`create_stage_in_memory`	bool	required	`true`	Create USD Stage in memory to speed up startup
`launch_config`	LaunchConfig	required	—	Isaac Sim AppLauncher startup parameters; see LaunchConfig
`physics_config`	PhysicsConfig	required	—	PhysX physics engine parameters; see PhysicsConfig
`render_config`	RenderConfig	required	—	Rendering parameters; see RenderConfig

classLaunchConfigfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`headless`	bool	required	`false`	Headless mode, no GUI window; suitable for server/training environments
`livestream`	int	required	`0`	Remote livestream mode ⚠0=disabled / 1=public network / 2=local network
`enable_cameras`	bool	required	`true`	Whether to enable camera rendering pipeline; must be true when collecting image data
`device`	string	required	`cuda`	Compute device ⚠cpu or cuda / cuda:<index>

classPhysicsConfigfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`solver_type`	int	required	`1`	Physics solver type ⚠0=PGS (projected Gauss-Seidel) / 1=TGS (temporal Gauss-Seidel, more accurate)
`min_position_iteration_count`	int	required	`1`	Min position constraint iterations per step
`max_position_iteration_count`	int	required	`255`	Max position constraint iterations per step
`min_velocity_iteration_count`	int	required	`0`	Min velocity constraint iterations per step
`max_velocity_iteration_count`	int	required	`255`	Max velocity constraint iterations per step
`enable_ccd`	bool	required	`false`	Continuous collision detection (CCD); prevents fast objects from tunneling, but reduces performance
`enable_stabilization`	bool	required	`false`	Physics stabilization to reduce micro-jitter
`enable_enhanced_determinism`	bool	required	`false`	Enhanced determinism mode; trades performance for better reproducibility
`bounce_threshold_velocity`	float	required	`0.5`	Bounce threshold velocity
`friction_offset_threshold`	float	required	`0.04`	Friction offset threshold
`friction_correlation_distance`	float	required	`0.025`	Friction correlation distance
`gpu_max_rigid_contact_count`	int	required	`8388608`	GPU max rigid contact count (2²³)
`gpu_max_rigid_patch_count`	int	required	`163840`	GPU max rigid patch count (5×2¹⁵)
`gpu_found_lost_pairs_capacity`	int	required	`2097152`	GPU found/lost pairs capacity (2²¹)
`gpu_found_lost_aggregate_pairs_capacity`	int	required	`33554432`	GPU found/lost aggregate pairs capacity (2²⁵)
`gpu_total_aggregate_pairs_capacity`	int	required	`2097152`	GPU total aggregate pairs capacity (2²¹)
`gpu_collision_stack_size`	int	required	`67108864`	GPU collision stack size (2²⁶)
`gpu_heap_capacity`	int	required	`67108864`	GPU heap capacity (2²⁶)
`gpu_temp_buffer_capacity`	int	required	`16777216`	GPU temp buffer capacity (2²⁴)
`gpu_max_num_partitions`	int	required	`8`	GPU max number of partitions
`gpu_max_soft_body_contacts`	int	required	`1048576`	GPU max soft body contacts (2²⁰)
`gpu_max_particle_contacts`	int	required	`1048576`	GPU max particle contacts (2²⁰)
`solve_articulation_contact_last`	bool	required	`false`	Whether to solve articulation contacts last

classRenderConfigfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`enable_translucency`	bool	required	`false`	Enable translucency rendering
`enable_reflections`	bool	required	`false`	Enable reflections
`enable_global_illumination`	bool	required	`true`	Enable global illumination
`antialiasing_mode`	string	required	`DLSS`	Antialiasing mode ⚠Off / FXAA / DLSS / TAA / DLAA
`enable_dlssg`	bool	required	`false`	Enable DLSS frame generation
`enable_dl_denoiser`	bool	required	`true`	Enable deep learning denoiser
`dlss_mode`	int	required	`0`	DLSS quality mode ⚠0 / 1 / 2 / 3
`enable_direct_lighting`	bool	required	`true`	Enable direct lighting
`samples_per_pixel`	int	required	`1`	Samples per pixel
`enable_shadows`	bool	required	`true`	Enable shadows
`enable_ambient_occlusion`	bool	required	`true`	Enable ambient occlusion
`dome_light_upper_lower_strategy`	int	required	`0`	Dome light upper/lower strategy ⚠0 / 3 / 4
`carb_settings`	dict[str, Any]	optional	`{}`	Custom Carbonite render settings
`rendering_mode`	string	optional	`performance`	Rendering quality mode ⚠performance / balanced / quality

MuJoCo Backend (stereotype: mujoco)

When stereotype is mujoco, the config class is MuJoCoConfig. Uses the MuJoCo physics engine; runs on CPU only.

classMuJoCoConfigstereotypemujocofastsim/simulators/mujoco/mujoco_config.py

Field	Type	Required	Default	Description / Constraints
`headless`	bool	required	`false`	Headless mode, no GUI viewer
`render_width`	int	required	`640`	Render width in pixels
`render_height`	int	required	`480`	Render height in pixels
`gravity`	list[3]	required	`[0, 0, -9.81]`	Gravity vector [x, y, z] in m/s²

PyBullet Backend (stereotype: pybullet)

When stereotype is pybullet, the config class is PyBulletConfig. Uses PyBullet for CPU-only simulation, ideal for lightweight testing and OMPL planning.

classPyBulletConfigstereotypepybulletfastsim/simulators/pybullet/pybullet_config.py

Field	Type	Required	Default	Description / Constraints
`headless`	bool	required	`true`	Headless mode, no GUI viewer (PyBullet defaults to headless)
`gravity`	list[3]	required	`[0, 0, -9.81]`	Gravity vector [x, y, z] in m/s²
`render_width`	int	required	`640`	Render width in pixels
`render_height`	int	required	`480`	Render height in pixels

Example

simulation:
  stereotype: isaaclab
  dt: 0.0166667
  initialize_steps: 60
  device: cuda:0
  render_interval: 1
  gravity: [0.0, 0.0, -9.81]
  create_stage_in_memory: true
  launch_config:
    headless: false
    livestream: 0
    enable_cameras: true
    device: cuda
  physics_config:
    solver_type: 1
    min_position_iteration_count: 1
    max_position_iteration_count: 255
    enable_ccd: false
    enable_stabilization: false
  render_config:
    antialiasing_mode: DLSS
    enable_shadows: true
    rendering_mode: performance

Common Errors

Error message	Cause	Fix
`Simulation config is required`	Missing simulation block or stereotype field not provided	Add a complete simulation config block with a valid stereotype
`Invalid simulator stereotype`	stereotype value not found in the UniSim registry	Run fastsim show-registry to see available backends; custom backends need scan_project enabled

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