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)Example Common errors

Top-level Fields3

Field	Type	Required	Default	Description / Constraints
`stereotype`	string	required	—	Simulation backend identifier (e.g. isaaclab); 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
`intiailize_steps`	int	optional	`0`	Initialization steps after reset to let the physics world stabilize before the task begins ⚠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	optional	`cuda:0`	Compute device ⚠cpu or cuda:<index> (e.g. cuda:0, cuda:1)
`render_interval`	int	optional	`1`	Render one frame every N physics steps ⚠Must be >= 1
`gravity`	list[3]	optional	`[0.0, 0.0, -9.81]`	Gravity vector [x, y, z] in m/s²
`create_stage_in_memory`	bool	optional	`true`	Create USD Stage in memory to speed up startup
`launch_config`	LaunchConfig	optional	—	Isaac Sim AppLauncher startup parameters; see LaunchConfig
`physics_config`	PhysicsConfig	optional	—	PhysX physics engine parameters; see PhysicsConfig
`render_config`	RenderConfig	optional	—	Rendering parameters; see RenderConfig

classLaunchConfigfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`headless`	bool	optional	`false`	Headless mode, no GUI window; suitable for server/training environments
`width`	int	optional	`1280`	Render window width in pixels; ignored when headless is true
`height`	int	optional	`720`	Render window height in pixels
`anti_aliasing`	int	optional	`0`	Anti-aliasing level ⚠0=off / 1=FXAA / 2=TAA
`enable_cameras`	bool	optional	`true`	Whether to enable camera rendering pipeline; must be true when collecting image data

classPhysicsConfigfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`solver_type`	int	optional	`1`	Physics solver type ⚠0=PGS (projected Gauss-Seidel) / 1=TGS (temporal Gauss-Seidel, more accurate)
`num_position_iterations`	int	optional	`4`	Position constraint iterations per step; higher = more accurate but slower
`num_velocity_iterations`	int	optional	`1`	Velocity constraint iterations per step
`enable_ccd`	bool	optional	`false`	Continuous collision detection (CCD); prevents fast objects from tunneling, but reduces performance
`enable_stabilization`	bool	optional	`true`	Physics stabilization to reduce micro-jitter
`gpu_max_soft_body_contacts`	int	optional	`1048576`	GPU max soft body contacts (2²⁰); adjust for soft body simulations
`gpu_max_particle_contacts`	int	optional	`1048576`	GPU max particle contacts (2²⁰); adjust for soft body simulations

classRenderConfigfastsim/simulators/isaaclab/isaaclab_config.py

Field	Type	Required	Default	Description / Constraints
`enable_rtx_rendering`	bool	optional	`false`	Enable RTX ray-tracing rendering; higher quality but significantly higher GPU usage

Example

simulation:
  stereotype: isaaclab
  dt: 0.0166667
  intiailize_steps: 30
  device: cuda:0
  render_interval: 1
  gravity: [0.0, 0.0, -9.81]
  create_stage_in_memory: true
  launch_config:
    headless: false
    width: 1280
    height: 720
    enable_cameras: true
  physics_config:
    solver_type: 1
    num_position_iterations: 4
    enable_ccd: false
  render_config:
    enable_rtx_rendering: false

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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