# MIT Mini Cheetah URDF Tutorial

## Overview
This tutorial demonstrates serving a URDF (Unified Robot Description Format) file locally to visualize the MIT Mini Cheetah robot in Vuer with animated leg movements.

## Directory Structure

Set up your assets directory:

```
assets/mini_cheetah/
├── meshes/
│   ├── mini_abad.obj
│   ├── mini_body.obj
│   ├── mini_lower_link.obj
│   └── mini_upper_link.obj
└── mini_cheetah.urdf
```

## Download Assets

Use wget to fetch the URDF and mesh files:

```bash
mkdir -p assets/mini_cheetah/meshes
cd assets/mini_cheetah

# Download URDF file
wget https://raw.githubusercontent.com/vuer-ai/vuer/main/assets/mini_cheetah/mini_cheetah.urdf

# Download mesh files
cd meshes
wget https://raw.githubusercontent.com/vuer-ai/vuer/main/assets/mini_cheetah/meshes/mini_abad.obj
wget https://raw.githubusercontent.com/vuer-ai/vuer/main/assets/mini_cheetah/meshes/mini_body.obj
wget https://raw.githubusercontent.com/vuer-ai/vuer/main/assets/mini_cheetah/meshes/mini_lower_link.obj
wget https://raw.githubusercontent.com/vuer-ai/vuer/main/assets/mini_cheetah/meshes/mini_upper_link.obj
```

## Complete Code Example

```python
import math
import asyncio
from vuer import Vuer
from vuer.schemas import Scene, Urdf, AmbientLight, Movable, PointLight

# Configure app to serve static files from assets directory
app = Vuer(static_root="assets/mini_cheetah")

@app.spawn(start=True)
async def main(session):
    # Setup scene with lighting
    session.set @ Scene(
        AmbientLight(intensity=0.8),
        Movable(
            PointLight(
                intensity=2.0,
                position=[1, 2, 1],
                key="point-light-1",
            )
        ),
        Movable(
            PointLight(
                intensity=2.0,
                position=[-1, 2, -1],
                key="point-light-2",
            )
        ),
    )

    # Animation loop
    for i in range(1000):
        # Calculate joint angles using sine waves
        hip_angle = 0.5 * math.sin(i * 0.1)
        thigh_angle = 0.785 - 0.25 * math.sin(i * 0.1)
        calf_angle = -1.5 + 0.5 * math.sin(i * 0.1)

        # Update robot with animated joints
        session.upsert @ Urdf(
            src="/static/mini_cheetah.urdf",
            position=[0, 0, 0],
            rotation=[0, 0, 0],
            jointValues={
                # Front Left leg
                "FL_hip_joint": hip_angle,
                "FL_thigh_joint": thigh_angle,
                "FL_calf_joint": calf_angle,

                # Front Right leg
                "FR_hip_joint": -hip_angle,
                "FR_thigh_joint": thigh_angle,
                "FR_calf_joint": calf_angle,

                # Rear Left leg
                "RL_hip_joint": hip_angle,
                "RL_thigh_joint": thigh_angle,
                "RL_calf_joint": calf_angle,

                # Rear Right leg
                "RR_hip_joint": -hip_angle,
                "RR_thigh_joint": thigh_angle,
                "RR_calf_joint": calf_angle,
            },
            key="mini-cheetah",
        )

        # Update at ~60 FPS
        await asyncio.sleep(0.016)

app.run()
```

## Joint Control

The Mini Cheetah has 12 joints (3 per leg):

- **Hip joint**: Abduction/adduction (side-to-side movement)
- **Thigh joint**: Hip flexion/extension (forward/backward)
- **Calf joint**: Knee flexion/extension

## Animation Details

The example creates a walking motion using sinusoidal functions:

```python
hip_angle = 0.5 * math.sin(i * 0.1)
thigh_angle = 0.785 - 0.25 * math.sin(i * 0.1)
calf_angle = -1.5 + 0.5 * math.sin(i * 0.1)
```

## Expected Result

When executed correctly, the tutorial produces a 3D visualization of the Mini Cheetah robot with animated leg movements displayed in a web interface at `http://localhost:8012`.

## Troubleshooting

### Robot not appearing
- Verify all mesh files are downloaded
- Check that `static_root` points to the correct directory
- Ensure URDF file references correct mesh paths

### Animation not smooth
- Adjust the sleep interval (currently 0.016s for ~60 FPS)
- Reduce animation speed by changing the multiplier in `i * 0.1`

## Source

Documentation: https://docs.vuer.ai/en/latest/tutorials/robotics/urdf_mini_cheetah.html