Feature: ID:004 - Simulate Multi-Body Physics - Base

Description:

Features needed to support Simulate Multi-Body physics. This feature enables simulation of physically accurate motion and collisions for props and dynamic assets that have multibody bodies that need to be joined or simulated together. The enables real world “joints” to describe how two bodies work together. It is suitable for testing, validation, or reference applications where basic physical interactions are required.

Neutral Format

Version 0.1.0

Details

Property	Value
Internal ID	FET004_BASE_NEUTRAL

Used in Profiles

This version is used in the following profiles:

• Prop Robotics Neutral Profile (v0.1.0) - Used for multi-body dynamics with joint and articulation support

Requirements

Property	Value
Dependency	ID:003 - RBD Physics - Base - Neutral Format - v0.1.0

• Capability: Physics-Bodies/Physics-Joints

  • Requirements

    • Joint-Capability

      • JT.001 | Version 0.1.0

      • Rule | Implementation

    • Articulation-No-Nesting

      • JT.ART.002 | Version 0.1.0

      • Rule | Implementation

    • Articulation-Not-On-Kinematic-Body

      • JT.ART.003 | Version 0.1.0

      • Rule | Implementation

    • Articulation-Not-On-Static-Body

      • JT.ART.004 | Version 0.1.0

      • Rule | Implementation

    • Joint-Body-Target-Exists

      • JT.002 | Version 0.1.0

      • Rule | Implementation

    • Joint-No-Multiple-Body-Targets

      • JT.003 | Version 0.1.0

      • Rule | Implementation

• Capability: Physics_Bodies/Physics_Rigid_Bodies

  • Requirements:

    • Multibody-Capability

      • RB.MB.001 | Version 0.1.0

      • Rule | Implementation

Pipelines Supported for this Feature

Source file type:

• .blend

  • Via Blender SimReady Add-ons

• .mjcf

  • Via Blender SimReady Add-ons + MJCF2USD Tool

• .step

  • Via Blender SimReady Add-ons + CAD Converter

MultiBody | Rigidbody Samples (Neutral)

• simready_usd/sm_obs_workbench_tool_a01_01.usd

• simready_usd/sm_obs_electricians_large_tool_box_a01_01.usd

• simready_usd/sm_obs_joystick_a01_01.usd

• simready_usd/sm_obs_lamp_revolute_a01_01.usd

Test Process

None.

NVIDIA Physx Format

Version 0.1.0

Details

Property	Value
Internal ID	FET004_BASE_PHYSX
Proprietary Techs	Physx

Used in Profiles

This version is used in the following profiles:

• Prop Robotics Physx Profile (v0.1.0) - Used for advanced multi-body dynamics with PhysX joint and articulation system

Requirements

Property	Value
Dependency	ID:003 - RBD Physics - Base - Nvidia Physx Format - v0.1.0
Dependency	ID:004 - Simulate Multi-Body Physics - Base - Neutral Format - v0.1.0

No additional requirements.

Pipelines Supported for this Feature

Source file type:

• .usd

  • Via CIP.

  • Convert from Neutral Format - Version 0.1.0.

MultiBody | Rigidbody Samples (Physx)

MultiBody | Robot Rigidbody Samples (Physx)

• simready_physx_usd/sm_obs_workbench_tool_a01_01.usd

• simready_physx_usd/sm_obs_electricians_large_tool_box_a01_01.usd

• simready_physx_usd/sm_obs_joystick_a01_01.usd

• simready_physx_usd/sm_obs_lamp_revolute_a01_01.usd

Test Process

• Obtain Isaac Sim

  • 4.5 is public and can be downloaded here

  • 5.0 requires users to build on their systems, you can follow the docs here

• Find directory where Isaac Sim was installed

  • Launch isaacsim.bat

  • In Isaac Sim, open this usd: test stage

    • Can be manually located here: nv_core/testing_tools/testing_data/runtime_physics_tests.usda

  • Activate correct prim (right click + activate)

    • select on of these prims:

      • /World/Drop_On_Ground_Plane

      • /World/Drop_On_Tilted_Plane

    • 

    • Right-click on selected prim for context menu and click “Activate”

    • 

  • Drill down into activated hierarchy, there should be a prim called “StartPoint”

    • or the direct prim path is: /World/Drop_On_Ground_Plane/StartPoint

  • Select that prim

  • Right-click, add reference to (path/to/asset/in_question.usd)

  • 

• Hit play button in UI.

  • Press play to start sim

  • Warnings will occur based on collider schema, this is expected

• Expected result:

  • item should fall down and stop and settle after 5 seconds.

  • Joints should move as expected

    • Jointed assets should not disconnect

    • Item should be splayed out in some form

  • Video Examples:

    • Drop test results link

    • Sloped Drop test results link

Robot PhysX Format (FET004_ROBOT_PHYSX)

This variant is used in Robot-Body profiles (e.g. Robot-Body-Physx, Robot-Body-Runnable, Robot-Body-Isaac) for multi-body robot physics with PhysX. It uses the same multi-body and joint requirements as the base PhysX format, but with a different set of collision requirements.

RB.COL.001 exclusion

RB.COL.001 (“Colliding Gprims must apply the Collision API”) is not enforced for FET004_ROBOT_PHYSX.

• Reason: RB.COL.001 is too strict for Omniverse/Isaac Sim robot assets. In practice, nesting for CollisionAPI is allowed (e.g. collision shapes under non-Gprim hierarchy or applied in ways that RB.COL.001 would reject).

• Effect: The Robot PhysX feature does not include RB.COL.001 in its requirement set. It does include RB.COL.002, RB.COL.003, and RB.COL.004 (mesh collision API, collider mesh, uniform scale), plus the other rigid-body and joint requirements listed in the feature JSON.

When authoring or validating robot USDs for Robot-Body profiles, do not require RB.COL.001 compliance; the validator configuration for this feature omits it by design.