Tutorial 3: Inspect Asset

You’ve seen how the Inspire Hand is built from multiple USD files (Tutorial 2). Next we inspect and validate that asset: joints, mass and inertia, and collision meshes. Skipping this step means you’re tuning in the dark—wrong masses or misaligned inertia can cause unstable or unrealistic motion even when joint parameters look correct, and the wrong collider type can slow the simulation or produce confusing contact behavior. Isaac Sim’s joint visualizer, Physics Debugger, and collider visualization give you a clear picture of the asset before you filter collision pairs or tune drives.

Learning Objectives

In this tutorial, you will:

• Enable the joint visualizer and interpret joint types (Fixed, Revolute, Mimic) in the Stage.

• Enable mass and inertia visualization and verify body axes and principal inertia so the hand’s dynamics match its geometry.

• Verify collision meshes and collider types so you know what collider shape approximations are made.

Prerequisites

• Complete Tutorial 2: Asset Structure (Tutorial 2: Asset Structure).

• Have the Inspire Hand scene open in Isaac Sim with the PhysX variant selected.

Module 2.1: Enable Joint Visualizer

Because we’re tuning for the PhysX backend, load the hand with the PhysX variant. Then enable joint visualization to see joint locations and types at a glance.

Viewport Navigation in Isaac Sim

• Orbit the camera: Hold Alt and left mouse button, then drag.

• Rotate in place (look around): Hold right mouse button and move the mouse.

• Zoom: Hold Alt and right mouse button (or use the scroll wheel).

• Pan: Hold the middle mouse button and drag.

• Focus the camera on a prim: Select the desired prim in the Stage panel, then press F.

Use these controls to efficiently explore and inspect the Inspire Hand model as you follow the instructions below.

1. In IsaacSim/Samples/Rigging/Inspire/module_1_start/, open inspire_hand.usda in Isaac Sim.

2. Select the top-level inspire_hand prim.

3. In the Property panel, scroll to Variants and select PhysX.

1. Go to Eye > Show by Type > Physics > Joints to enable joint visualization.

In the viewport, the Inspire Hand should now have gizmos identifying the locations and types of each joint.

Examine the joints — In the Stage panel, under the /Physics scope, find right_index_1_joint—a Revolute joint responsible for the base motion of the index finger, represented by a circular icon in the viewport. Also locate right_index_rubber_1_joint, which is a Fixed joint attaching the lower index rubber pad to its link, shown as a rectangular icon in the visualization. The right_index_2_joint is a mimic joint that references the movement of right_index_1_joint (we’ll cover mimic joints in more detail in Tutorial 5). Understanding how these joints function and their naming conventions will be valuable when tuning the drives in Tutorials 5 and 6.

Module 2.2: Verify Mass and Inertia Properties

Mass and inertia define how each link responds to forces. If the principal inertia axes are misaligned with the link geometry, or if mass values are too small or too large, the hand can behave unrealistically. The Physics Debugger lets you visualize body axes and Body Mass Axes (principal inertia) so you can spot problems before running the simulation.

1. Open Utilities > Physics Debugger. The Physics Debug panel appears.

1. In Simulation Debug Visualization: - Check Enabled. - Check Body Axes to show coordinate frames. - Check Body Mass Axes to show principal inertia axes.

2. In Simulation Control, click Step to run one simulation frame and display the visualization.

Warning

Avoid pressing Play at this stage, as it may cause Isaac Sim to crash. Instead, use Simulation Control to either Run the physics simulation or Step through it one frame at a time.

1. For each link, you can now verify: - Mass centers sit appropriately within the link. - Principal inertia axes align with the link geometry. - Inertia values look plausible (not excessively small or large).

Note

Misaligned principal inertia axes can cause unstable or unrealistic motion. The image below shows an example of misalignment.

Alternative Method: Inspecting Mass and Inertia via the Physics Toolbar

You can also inspect mass and inertia properties using the Physics Toolbar:

1. Go to Tools > Physics Toolbar.

1. In the toolbar, toggle on both the Rigid Body Selection Mode (cube icon) and the Mass Distribution Manipulator (balance icon).

2. In the viewport, select any rigid body prim on the hand. The Mass Properties Info will be displayed, providing details about the total mass, center of mass, principal axis, and diagonal inertia directly in the viewport.

This method lets you quickly inspect and debug mass distribution for any body in the scene without navigating to the Property panel.

Module 2.3: Verify Collision Meshes

The shapes you see in the viewport aren’t necessarily what the physics engine uses for contact—that’s determined by the collision meshes (colliders). Before we filter collision pairs in Tutorial 4, we inspect and verify the colliders: colliders are color-coded green for rigid bodies and magenta for static bodies.

1. Go to Eye > Show by Type > Physics > Colliders > All to visualize all collision shapes.

Setting collider types affects performance and fidelity. You can mix types on one asset. For dexterous hands, Convex Hull is often used for parts that do not need high accuracy (e.g. palm), and Convex Decomposition for parts that need accurate contact (e.g. fingertips). Convex Decomposition gives the best shapes but costs more than Convex Hull or geometry-based colliders. In this tutorial we use Convex Hull for all parts.

Summary

This tutorial covered:

• Enabling the joint visualizer and identifying joint types (Fixed, Revolute, Mimic) in the Stage—the same structure you’ll tune in Tutorials 5 and 6.

• Using the Physics Debugger to visualize body axes and principal inertia and verifying that mass centers and inertia alignment look correct for each link.

• Turning on collider visualization and confirming the collider strategy (Convex Hull for this series), so you know what shapes will collide when self-collisions are enabled in Tutorial 4.

Continue to Tutorial 4: Collider Pairs (Tutorial 4: Collider Pairs) to identify problematic collision pairs with the Physics Debugger and add filtered pairs.