Robot-Body-Runnable Profile USD Authoring Guide

This document describes how to author a USD asset that conforms to the Robot-Body-Runnable profile. It consolidates the required feature set, USD properties, naming conventions, and composition expectations for runnable robot assets (PhysX multibody with robot core runnable).

Profile definition

The Robot-Body-Runnable profile includes the following feature set:

[Robot-Body-Runnable]
"1.0.0" = {features = [
    {"FET_001_STANDARD" = {version = "0.1.0"}}, # Minimal
    {"FET_003_STANDARD" = {version = "0.1.0"}}, # RBD Physics (Standard)
    {"FET_004_ROBOT_PHYSX" = {version = "0.1.0"}}, # Multi-body physics (Robot PhysX)
    {"FET_021_ISAAC" = {version = "0.3.0"}}, # Robot Core
    {"FET_022_PHYSX" = {version = "0.1.0"}}, # Driven Joints (PhysX)
    {"FET_024_PHYSX" = {version = "0.1.0"}}, # Articulation
]}

Required USD properties and schemas

Stage metadata (required)

• defaultPrim must be set on every layer.

• upAxis = "Z" and metersPerUnit = 1 must be set on every stage.

PhysX rigid bodies and colliders (required)

• Apply PhysicsRigidBodyAPI to any simulated rigid body prim.

• Apply PhysicsCollisionAPI to collision-enabled prims.

• Use a valid physics:approximation type for mesh colliders (e.g. convex hull or SDF).

• Rigid body prims must be UsdGeomXformable.

Multi-body joints (required)

• Use UsdPhysicsJoint prims (or subtypes) to connect rigid bodies.

• Author rel physics:body0 and rel physics:body1 relationships.

• Apply PhysxJointAPI when authoring PhysX-specific joint properties.

Driven joints (required)

• Apply PhysicsDriveAPI:* or PhysxMimicJointAPI:* to driven joints.

• Apply PhysicsJointStateAPI:* to driven joints.

• Author physxJoint:maxJointVelocity with a positive value.

• When a joint has both drive and mimic APIs, drive stiffness and damping must be exactly 0.0.

• Mimic joints must set a single valid physxMimicJoint:*:referenceJoint and author physxMimicJoint:*:gearing, physxMimicJoint:*:naturalFrequency, and physxMimicJoint:*:dampingRatio.

Articulation root (required)

Apply PhysicsArticulationRootAPI to the root prim of the articulation:

def Xform "Robot" (
    prepend apiSchemas = ["PhysicsArticulationRootAPI"]
)
{
}

Robot core (runnable) requirements

Robot core (FET_021_ISAAC) enforces robot naming, robot schema metadata, robot type, and root-joint pinning suitable for runnable robot assets. Refer to the capability docs for robot core requirements.

Stage composition requirements

This profile does not require Isaac Sim–specific composition. A single-layer USD is acceptable. If you choose to split layers, keep all references and payloads relative and consistent.

Naming conventions

Prim naming

• Choose either camelCase or snake_case and use it consistently.

• Avoid spaces, special characters, and reserved keywords.

• Use descriptive, purpose-driven names.

• Use prefixes by prim type when appropriate (e.g., mesh_, material_).

File naming

• Use lowercase file names.

• Use .usd, .usda, .usdc, or .usdz as appropriate.

• Use underscores or hyphens; avoid spaces and special characters.

• Avoid reserved names (e.g., CON, PRN, AUX, NUL).

• Use version numbers when appropriate (e.g., _v1.0).

Validation metadata (recommended)

Include profile metadata in customLayerData to simplify validation workflows:

customLayerData = {
    dictionary SimReady_Metadata = {
        dictionary validation = {
            string profile = "Robot-Body-Runnable"
            string profile_version = "1.0.0"
        }
    }
}

References

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/profiles/robot_body_runnable.toml

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_003_STANDARD.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_004_ROBOT_PHYSX.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_021_ISAAC.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_022_STANDARD.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/features/FET_024_STANDARD.md

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/physics_driven_joints/

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/physics_bodies/base_articulation/

• nv_core/tiers/simready_foundation_tier_core/simready/foundation/tier_core/capabilities/core/naming_paths/