> ## Documentation Index
> Fetch the complete documentation index at: https://docs.gizmo.antimlabs.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Joints and Physics

> Joint types, axis conventions, and physics metadata in Gizmo

Gizmo uses a consistent, robotics-oriented joint model.

## Joint Types

| Joint     | Common Use                              |
| --------- | --------------------------------------- |
| Revolute  | Doors, lids, knobs, levers, wheels      |
| Prismatic | Drawers, sliders, pistons, gripper jaws |
| Spherical | Gimbals, shoulders, ball joints         |
| Fixed     | Welded or rigid attachments             |

## Axis Convention

Joint axes are authored in the **asset-local frame**.

| Object                  | Joint                           |
| ----------------------- | ------------------------------- |
| Cabinet door            | Revolute, vertical Z-axis hinge |
| Drawer                  | Prismatic, forward/back axis    |
| Oven or dishwasher door | Revolute, bottom hinge          |
| Knob or dial            | Revolute around stem direction  |
| Wheel                   | Revolute around wheel normal    |

## Physics Metadata

For each primitive, Gizmo computes:

* Material density
* Analytical or estimated volume
* Mass
* Inertia tensor
* Friction
* Restitution
* Collision approximation
* V-HACD convex decomposition for complex collision geometry