Requirements

Summary

• The rigid body schema must be applied to any xformable prim that represent a rigid physical object

• Colliding Gprims need to have the Collision API applied

• Each rigid body or it’s descendant colliders, should have the mass API applied.

Granularity

If joints are not present, each rigid body will be simulated as a free body. Only create multiple rigid bodies in an asset if they are either connected by joints or if they are intended to be simulated without being connected to each other.

Schema / OpenUSD Specification

Rigid Body Physics are applied using the following two schemas that are part of the core OpenUSD specification.

• USD Rigid Bodies

• USD Physics Collision Shapes

USDA Sample

(
    kilogramsPerUnit = 1
)

def Xform "RobotHead" (
    prepend apiSchemas = ["PhysicsRigidBodyAPI", "PhysicsMassAPI"]
    ) {

    physics:mass = 10.0

    def Mesh "Head" (
        prepend apiSchemas = ["PhysicsCollisionAPI"]
    ) {
        # ...
    }

    def Mesh "Jaw" (
        prepend apiSchemas = ["PhysicsCollisionAPI"]
    ) {
        # ...
    }
}

def Mesh "GroundPlane" (
    prepend apiSchemas = ["PhysicsCollisionAPI"]
) {}

Requirements

Tags	Summary	Compatibility	Validator
🔑	MuJoCo collision shapes must apply MjcCollisionAPI on valid USD collision geometry.	other	MuJoCoColliderAPIChecker
🔑	MuJoCo mesh collision data must use valid MjcMeshCollisionAPI and convex-hull mesh collision authoring.	other	MuJoCoMeshCollisionAPIChecker
🔑	Newton colliders must use a valid Newton collision schema.	other	NewtonColliderAPIChecker
🔑	Authored Newton SDF attributes must be valid.	other	NewtonSDFAttributesChecker
🔑	NewtonMassAPI must be applied on an Xformable, and any authored Newton mass attributes must be valid.	other	NewtonMassAttributesChecker
🔑	CollisionAPI may only be applied to a UsdGeom Gprim or to an Xform that has PhysxMeshMergeCollisionAPI and whose collisionmeshes collection includes at least one Gprim.	physx
🔑	Assets must contain at least one rigid body	open-usd
🔑	Invisible collision meshes must have their purpose attribute set to ‘guide’ to be properly excluded from rendering.	open-usd
🔑	Colliding Gprims must apply the Collision API.	open-usd
🔑	Assets must contain at least two rigid bodies	open-usd
✅	MeshCollisionAPI may only be applied to a UsdGeom Mesh or to a prim that has PhysxMeshMergeCollisionAPI. CollisionAPI is required whenever MeshCollisionAPI is applied.	physx
✅	Rigid bodies have to be UsdGeomXformable prims.	open-usd	latest+
✅	Rigid bodies cannot be part of a scene graph instance.	open-usd	latest+
✅	Rigid bodies can not be nested unless xformOp reset xform stack is used.	open-usd	latest+
✅	Rigid bodies have to be UsdGeomXformable prims without skew matrix.	open-usd	latest+
✅	Rigid bodies should not be nested unless they are connected by a joint.	open-usd
✅	UsdPhysicsMeshCollisionAPI may only be applied to UsdGeom.Mesh prims, and any prim with MeshCollisionAPI must also have UsdPhysicsCollisionAPI applied.	open-usd	RigidBodyColliderMeshChecker
✅	The Mesh Collision API can only be assigned to Mesh Prims.	open-usd
✅	The collision shape scale must be uniform for the following geometries: Sphere, Capsule, Cylinder, Cone & Points.	open-usd	latest+
💎	Rigid bodies or their descendant collision shapes must have a mass specification.	open-usd
💎	Rigid bodies or their descendent collision shapes may have detailed mass properties including density, center of mass, and inertia tensor. When authored, these detailed mass properties must be internally consistent.	open-usd
💎	Every rigid body must have a valid (positive) physics:mass on itself or on at least one of its child colliders. Nested rigid body subtrees are excluded from the traversal. Negative mass is always a failure.	open-usd
💎	Enabled rigid bodies must have collision geometry.	open-usd