Simulation overview¶

from strands_robots import Robot
sim = Robot("so100")   # preferred factory; 60+ actions as an AgentTool

For walkthroughs see Simulation overview.

World¶

Action	Key params	Notes
`create_world`	`timestep=0.002`, `gravity=[0,0,-9.81]`, `ground_plane=True`	Implicit on `Robot()`
`load_scene`	`scene_path`	Replace world with MJCF
`reset`	-	State to t=0, keep model
`get_state`	-	Sim time, joint positions, object poses
`destroy`	-	Tear down model, data, executor
`export_xml`	-	Serialise model to MJCF string

Action	Notes
`replace_scene_mjcf(xml)`	Swap entire world XML
`patch_scene_mjcf(ops)`	Incremental patches, no full recompile
`raycast(origin, direction, ...)`	Single ray–mesh intersection
`multi_raycast(rays, ...)`	Batch ray–mesh intersections

Action	Key params
`add_robot`	`robot_name`, `position=[0,0,0]`, `data_config=None`, `urdf_path=None`
`remove_robot`	`name`
`list_robots`	-
`get_robot_state`	`name` → joint positions, velocities, torques

Action	Key params
`add_object`	`name`, `shape="box"\\|"sphere"\\|"cylinder"\\|"plane"\\|"mesh"`, `size`, `position=[x,y,z]`, `color=[r,g,b,a]`, `orientation=[w,x,y,z]`, `mass=0.1`, `is_static=False`, `mesh_path=None` - `plane` requires `is_static=True`
`remove_object`	`name`
`move_object`	`name`, `position`, `orientation` (NOT `pos`/`quat`)
`list_objects`	-

Action	Key params
`add_camera`	`name`, `position`, `target`, `fov=60.0`, `width=640`, `height=480` - no `attach_to`/`fovy`/`lookat`
`remove_camera`	`name`

Robot-URDF cameras are auto-discovered on add_robot.

Action	Notes
`render(camera_name="default", width=None, height=None)`	PNG in `content[...]["image"]["source"]["bytes"]`; no `frame` key
`render_depth(camera_name="default", width=None, height=None)`	Depth float32 in content; no `depth` key
`open_viewer` / `close_viewer`	Interactive MuJoCo passive viewer

Get a numpy frame

sim.get_observation(robot_name)[camera_name] → np.uint8 (H, W, 3)

Action	Key params
`step`	`n_steps=1` (max 100 000/call)
`set_gravity`	`gravity=[x,y,z]`
`set_timestep`	`timestep`
`get_contacts` / `get_contact_forces`	-
`apply_force`	`body_name`, `force`, `torque`, `point`
`get_jacobian`	`body_name` or `site_name` or `geom_name`
`get_mass_matrix`	-
`inverse_dynamics`	-
`forward_kinematics`	`body_name` (optional)
`save_state` / `load_state`	snapshot/restore full physics
`get_energy`	-
`get_sensor_data`	`sensor_name` (optional)

Action	Key params
`run_policy`	`robot_name` (required), `policy_provider="mock"`, `policy_config={}`, `policy_object=None`, `instruction=""`, `duration=10.0`, `control_frequency=50.0`, `action_horizon=8`, `n_steps=None`
`start_policy`	same args, async/non-blocking
`stop_policy`	`robot_name` (optional, defaults to `""`)
`list_policies_running`	-
`run_multi_policy`	`policies={robot: Policy}`, `instructions`, `duration`, `n_steps`
`eval_policy`	`robot_name` (required), `n_episodes=1`, `max_steps=300`, `success_fn=None`
`replay_episode`	`repo_id`, `robot_name=None`, `episode=0`

Action	Notes
`start_recording(repo_id, task="", fps=30, ...)`	LeRobot v3 (parquet+MP4); requires `[lerobot]` extra
`stop_recording(output_path=None)`	Finalise episode
`get_recording_status`	Episode, frame count, output dir
`start_cameras_recording(...)`	Plain MP4 via imageio-ffmpeg; `[sim-mujoco]` only, no lerobot
`stop_cameras_recording` / `get_cameras_recording_status`	-

Action	Key params
`randomize`	`randomize_colors=True`, `randomize_lighting=True`, `randomize_physics=False`, `randomize_positions=False`, `position_noise=0.02`, `color_range=(0.1,1.0)`, `friction_range=(0.5,1.5)`, `mass_range=(0.5,2.0)`, `seed=None`

Destructive - writes into model arrays. Recompile scene to undo.

Action	Notes
`list_urdfs`	Loaded URDFs/MJCFs in current world
`register_urdf(name, path)`	Register additional asset
`get_features(robot_name=None)`	Observation/action feature schema for recording