# Physics Sim

> Rigid body, soft body, and destruction setups in Blender including constraints, cell fracture debris, and baked caches via MCP.

- Skill: `arjun988/physics-sim` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add arjun988/physics-sim`
- Raw SKILL.md: https://api.skillmd.com/api/skills/arjun988/physics-sim/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- License: MIT
- Author: arjun988 (https://skillmd.com/u/arjun988)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/arjun988/physics-sim

---


# Physics Sim

Stable rigid/soft body setups. Motivated destruction. Baked caches.

## When to Use

- Rigid body interactions and collapses
- Soft body jiggle / rubber / simple soft props
- Destruction and debris (cell fracture / pre-cut shards)
- Pre-vis physics before VFX polish

## Workflow

```
Simplify collision meshes → Assign rigid/soft bodies
  → Constraints → Passive settings → Bake → Art-direct → Export cache
```

## Rigid Body Quick Rules

| Role | Settings notes |
|------|----------------|
| Active | Moving debris / props |
| Passive | Floors, walls, heavy anchors |
| Convex hull | Fast, approximate |
| Mesh | Accurate, heavier |

- Apply scale before sim
- Use margin appropriate to scale
- Collection: `COL_Physics_[Shot]`

## Constraints

- Hinge / fixed / motor for mechanical links
- Breakable constraints for destruction beats
- Name: `RBCON_[Object]_[Type]`

## Destruction Approach

```
1. Pre-cut shards (cell fracture or manual)
2. Island meshes as active rigid bodies
3. Passive shell until trigger frame
4. Animate trigger (force / keyframed activation)
5. Bake → cleanup interpenetrations
```

## Soft Body

- Prefer for simple soft props; use `cloth-sim` for garments
- Goal weights to retain shape
- Soft + collision object required

## Bake / Export

- Bake to cache before render
- Alembic/USD for cinematic debris
- For games: bake key poses or flipbook; rarely live Blender physics

## Constraints

### MUST DO
- Apply scale; use simplified colliders
- Bake before final delivery
- Trigger destruction intentionally (frame)

### MUST NOT DO
- High-res sculpt meshes as active colliders
- Unbounded shard counts
- Leave sims unbaked for final renders

## Reference Guide

| Topic | Reference | Load When |
|-------|-----------|----------|
| Rigid Body Presets | `references/rigid-body-presets.md` | When needed |
| Destruction Pipeline | `references/destruction-pipeline.md` | When needed |
| Sim Bake Checklist | `references/sim-bake-checklist.md` | When needed |