Physics

Backend selection

EmbodiChain exposes two physics backends, selected by the configuration type:

Backend	Python configuration	Execution and solver model	Start here
default	DefaultPhysicsCfg	CPU or GPU execution; Constraint Dynamics is the default solver.	Default Physics Backend
newton	NewtonPhysicsCfg	Newton through DexSim; DexUni is the coupled articulation/deformable path.	Newton Physics Backend

Both are integrated through DexSim’s runtime and Spawn SDK. default and newton are the only public backend identifiers. The renderer is selected separately by render_cfg; native-window and browser visualization settings control how the scene is displayed. Selecting Newton does not select a different camera renderer. headless=True closes the native window while permitting configured offscreen camera rendering.

Supported capabilities

This table describes the current EmbodiChain integration. A feature in an upstream solver does not imply that every asset or operation exposes it here.

Capability	Default	Newton
Rigid objects and articulations	Supported	Supported
Cloth and soft bodies	Unsupported	Supported on GPU
Manager rigid constraints	Supported	Unsupported
Camera and stereo camera	Supported	Supported
ContactSensor	Supported on CPU and GPU	Solver/device dependent
Differentiable simulation	Unsupported	semi_implicit only

Use Default for workflows needing its native rigid constraints or established Constraint Dynamics behavior. Use Newton for DexUni robot/deformable coupling, particle-based cloth or soft bodies, solver-specific experiments, or the supported differentiable path. For rigid robot tasks that can run on either backend, validate the target task with each configuration; shared APIs do not guarantee identical trajectories or contact responses.

See DexSim Unified Coupled Solver For Embodied AI for mixed articulation/deformable scenes and Newton Runtime Qualification for the detailed Newton support matrix.

physics: newton identifies the backend, not a fully qualified runtime. The resolved solver, device, scene contents, and requested operation determine the actual support boundary. See Newton Runtime Qualification for the solver/device matrix and the checks to perform after prepare().

Common configuration and devices

All backends inherit these parameters from PhysicsBackendCfg:

Parameter	Default	Meaning
physics_dt	0.01	Duration of one EmbodiChain physics step, in seconds.
device	"cpu" for Default; "cuda:0" for Newton	Compute device for physics and environment tensors. Solver/device restrictions still apply.
gravity	[0.0, 0.0, -9.81]	World-frame acceleration in m/s².

physics_cfg.device owns the backend default. An explicit SimulationManagerCfg(device=...) overrides it; the legacy sim_device argument is an alias. gpu_id selects the rendering GPU and supplies the index for an unindexed "cuda" device. Keep explicit compute and render GPU indices consistent with the intended deployment. Omitting Gym’s --device preserves the configured value or backend default; an explicit --device cpu also applies to Newton, subject to the selected solver and asset restrictions.

Python chooses a backend through physics_cfg. Gym files declare physics and a matching physics_config; an environment component owns both fields and its deployment cannot override either. --physics can confirm the file’s backend but cannot switch it. See Configuration Guide for paired configuration examples.

Physics, control, and solver time

Interval	Definition	Example
Physics step	physics_dt	0.01 s (100 Hz)
Gym control step	physics_dt * sim_steps_per_control	0.01 * 4 = 0.04 s (25 Hz)
Newton solver substep	physics_dt / num_substeps	0.01 / 10 = 0.001 s (1 kHz)

In this example, one control action spans four physics steps and forty Newton solver substeps. Increasing Newton’s num_substeps refines integration without changing the control period. Reducing physics_dt also changes the control period unless sim_steps_per_control is adjusted. Rendering and visualization publication have their own cadence and do not define the control frequency.

• Default Physics Backend
• Newton Physics Backend