---
name: urdf-sdf-model-710ec877d836
description: Expert skill for robot model creation and validation in URDF and SDF formats. Generate URDF files with proper link-joint hierarchy, create Xacro macros, calculate inertial properties, configure joint types, and validate models.
allowed-tools: Bash(*) Read Write Edit Glob Grep WebFetch
metadata:
  author: babysitter-sdk
  version: "1.0.0"
  category: robot-modeling
  backlog-id: SK-004
graph:
  domains: [domain:robotics]
  specializations: [specialization:robotics-simulation]
  skillAreas: [skill-area:motion-planning, skill-area:sensor-fusion]
  roles: [role:research-engineer]
---

# urdf-sdf-model

You are **urdf-sdf-model** - a specialized skill for robot model creation and validation in URDF (Unified Robot Description Format) and SDF (Simulation Description Format).

## Overview

This skill enables AI-powered robot modeling including:
- Generating URDF files with proper link-joint hierarchy
- Creating Xacro macros for modular robot descriptions
- Converting between URDF and SDF formats
- Calculating and setting inertial properties (mass, inertia tensors)
- Importing and optimizing mesh files (visual and collision)
- Configuring joint types (revolute, prismatic, continuous, fixed, floating)
- Setting up transmission and actuator definitions
- Adding sensor plugins and attachments
- Validating models with urdfdom and check_urdf
- Visualizing and debugging in RViz

## Prerequisites

- ROS/ROS2 with urdf packages
- xacro for macro processing
- urdfdom for validation
- Gazebo for SDF validation
- Mesh tools (MeshLab, Blender) for mesh optimization

## Capabilities

### 1. URDF Generation

Generate URDF files with proper structure:

```xml
<?xml version="1.0"?>
<robot name="my_robot" xmlns:xacro="http://www.ros.org/wiki/xacro">

  <!-- Materials -->
  <material name="blue">
    <color rgba="0.0 0.0 0.8 1.0"/>
  </material>

  <!-- Base Link -->
  <link name="base_link">
    <visual>
      <geometry>
        <box size="0.5 0.3 0.1"/>
      </geometry>
      <material name="blue"/>
    </visual>
    <collision>
      <geometry>
        <box size="0.5 0.3 0.1"/>
      </geometry>
    </collision>
    <inertial>
      <mass value="10.0"/>
      <origin xyz="0 0 0" rpy="0 0 0"/>
      <inertia ixx="0.0833" ixy="0" ixz="0"
               iyy="0.2167" iyz="0" izz="0.2833"/>
    </inertial>
  </link>

  <!-- Wheel Joint -->
  <joint name="wheel_joint" type="continuous">
    <parent link="base_link"/>
    <child link="wheel_link"/>
    <origin xyz="0.2 0.15 -0.05" rpy="-1.5708 0 0"/>
    <axis xyz="0 0 1"/>
    <limit effort="10" velocity="10"/>
    <dynamics damping="0.1" friction="0.1"/>
  </joint>

  <!-- Wheel Link -->
  <link name="wheel_link">
    <visual>
      <geometry>
        <cylinder radius="0.05" length="0.02"/>
      </geometry>
    </visual>
    <collision>
      <geometry>
        <cylinder radius="0.05" length="0.02"/>
      </geometry>
    </collision>
    <inertial>
      <mass value="0.5"/>
      <inertia ixx="0.0003" ixy="0" ixz="0"
               iyy="0.0003" iyz="0" izz="0.0006"/>
    </inertial>
  </link>

</robot>
```

### 2. Xacro Macros

Create modular robot descriptions with Xacro:

```xml
<?xml version="1.0"?>
<robot name="my_robot" xmlns:xacro="http://www.ros.org/wiki/xacro">

  <!-- Properties -->
  <xacro:property name="wheel_radius" value="0.05"/>
  <xacro:property name="wheel_width" value="0.02"/>
  <xacro:property name="wheel_mass" value="0.5"/>

  <!-- Inertia Macros -->
  <xacro:macro name="cylinder_inertia" params="m r h">
    <inertia ixx="${m*(3*r*r+h*h)/12}" ixy="0" ixz="0"
             iyy="${m*(3*r*r+h*h)/12}" iyz="0" izz="${m*r*r/2}"/>
  </xacro:macro>

  <xacro:macro name="box_inertia" params="m x y z">
    <inertia ixx="${m*(y*y+z*z)/12}" ixy="0" ixz="0"
             iyy="${m*(x*x+z*z)/12}" iyz="0" izz="${m*(x*x+y*y)/12}"/>
  </xacro:macro>

  <!-- Wheel Macro -->
  <xacro:macro name="wheel" params="prefix parent x_offset y_offset">
    <joint name="${prefix}_wheel_joint" type="continuous">
      <parent link="${parent}"/>
      <child link="${prefix}_wheel_link"/>
      <origin xyz="${x_offset} ${y_offset} 0" rpy="-1.5708 0 0"/>
      <axis xyz="0 0 1"/>
      <limit effort="10" velocity="10"/>
      <dynamics damping="0.1" friction="0.1"/>
    </joint>

    <link name="${prefix}_wheel_link">
      <visual>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_width}"/>
        </geometry>
        <material name="black"/>
      </visual>
      <collision>
        <geometry>
          <cylinder radius="${wheel_radius}" length="${wheel_width}"/>
        </geometry>
      </collision>
      <inertial>
        <mass value="${wheel_mass}"/>
        <xacro:cylinder_inertia m="${wheel_mass}" r="${wheel_radius}" h="${wheel_width}"/>
      </inertial>
    </link>

    <!-- Gazebo friction -->
    <gazebo reference="${prefix}_wheel_link">
      <mu1>1.0</mu1>
      <mu2>1.0</mu2>
      <kp>1e6</kp>
      <kd>1.0</kd>
    </gazebo>
  </xacro:macro>

  <!-- Instantiate wheels -->
  <xacro:wheel prefix="front_left" parent="base_link" x_offset="0.15" y_offset="0.12"/>
  <xacro:wheel prefix="front_right" parent="base_link" x_offset="0.15" y_offset="-0.12"/>
  <xacro:wheel prefix="rear_left" parent="base_link" x_offset="-0.15" y_offset="0.12"/>
  <xacro:wheel prefix="rear_right" parent="base_link" x_offset="-0.15" y_offset="-0.12"/>

</robot>
```

### 3. Inertia Calculations

Calculate inertia tensors for common geometries:

```python
import numpy as np

def box_inertia(mass, x, y, z):
    """Calculate inertia tensor for a box centered at origin."""
    ixx = mass * (y**2 + z**2) / 12
    iyy = mass * (x**2 + z**2) / 12
    izz = mass * (x**2 + y**2) / 12
    return {'ixx': ixx, 'iyy': iyy, 'izz': izz, 'ixy': 0, 'ixz': 0, 'iyz': 0}

def cylinder_inertia(mass, radius, height):
    """Calculate inertia tensor for a cylinder along z-axis."""
    ixx = mass * (3 * radius**2 + height**2) / 12
    iyy = mass * (3 * radius**2 + height**2) / 12
    izz = mass * radius**2 / 2
    return {'ixx': ixx, 'iyy': iyy, 'izz': izz, 'ixy': 0, 'ixz': 0, 'iyz': 0}

def sphere_inertia(mass, radius):
    """Calculate inertia tensor for a solid sphere."""
    i = 2 * mass * radius**2 / 5
    return {'ixx': i, 'iyy': i, 'izz': i, 'ixy': 0, 'ixz': 0, 'iyz': 0}

def mesh_inertia_from_stl(stl_file, mass, density=None):
    """Estimate inertia from STL mesh using convex hull approximation."""
    # Use trimesh or similar library for accurate calculation
    import trimesh
    mesh = trimesh.load(stl_file)
    mesh.density = density if density else mass / mesh.volume
    return mesh.moment_inertia
```

### 4. Joint Types Configuration

Configure different joint types:

```xml
<!-- Revolute Joint (limited rotation) -->
<joint name="arm_joint" type="revolute">
  <parent link="base"/>
  <child link="arm"/>
  <origin xyz="0 0 0.1" rpy="0 0 0"/>
  <axis xyz="0 1 0"/>
  <limit lower="-1.57" upper="1.57" effort="100" velocity="1.0"/>
  <dynamics damping="0.5" friction="0.1"/>
</joint>

<!-- Continuous Joint (unlimited rotation) -->
<joint name="wheel_joint" type="continuous">
  <parent link="base"/>
  <child link="wheel"/>
  <axis xyz="0 0 1"/>
  <limit effort="10" velocity="10"/>
</joint>

<!-- Prismatic Joint (linear motion) -->
<joint name="slider_joint" type="prismatic">
  <parent link="base"/>
  <child link="slider"/>
  <origin xyz="0 0 0"/>
  <axis xyz="0 0 1"/>
  <limit lower="0" upper="0.5" effort="50" velocity="0.5"/>
</joint>

<!-- Fixed Joint (no motion) -->
<joint name="sensor_mount" type="fixed">
  <parent link="base"/>
  <child link="sensor"/>
  <origin xyz="0.1 0 0.05" rpy="0 0 0"/>
</joint>
```

### 5. Sensor Attachments

Add sensors to the robot model:

```xml
<!-- Camera Sensor -->
<link name="camera_link">
  <visual>
    <geometry>
      <box size="0.02 0.05 0.02"/>
    </geometry>
  </visual>
</link>

<joint name="camera_joint" type="fixed">
  <parent link="base_link"/>
  <child link="camera_link"/>
  <origin xyz="0.2 0 0.1" rpy="0 0 0"/>
</joint>

<gazebo reference="camera_link">
  <sensor type="camera" name="camera">
    <update_rate>30.0</update_rate>
    <camera>
      <horizontal_fov>1.3962634</horizontal_fov>
      <image>
        <width>640</width>
        <height>480</height>
        <format>R8G8B8</format>
      </image>
      <clip>
        <near>0.02</near>
        <far>100</far>
      </clip>
    </camera>
    <plugin name="camera_plugin" filename="libgazebo_ros_camera.so">
      <ros>
        <namespace>/robot</namespace>
        <remapping>image_raw:=camera/image_raw</remapping>
        <remapping>camera_info:=camera/camera_info</remapping>
      </ros>
      <frame_name>camera_link</frame_name>
    </plugin>
  </sensor>
</gazebo>

<!-- LiDAR Sensor -->
<link name="lidar_link">
  <visual>
    <geometry>
      <cylinder radius="0.03" length="0.04"/>
    </geometry>
  </visual>
</link>

<gazebo reference="lidar_link">
  <sensor type="ray" name="lidar">
    <pose>0 0 0 0 0 0</pose>
    <visualize>true</visualize>
    <update_rate>10</update_rate>
    <ray>
      <scan>
        <horizontal>
          <samples>360</samples>
          <resolution>1</resolution>
          <min_angle>-3.14159</min_angle>
          <max_angle>3.14159</max_angle>
        </horizontal>
      </scan>
      <range>
        <min>0.1</min>
        <max>10.0</max>
        <resolution>0.01</resolution>
      </range>
    </ray>
    <plugin name="lidar_plugin" filename="libgazebo_ros_ray_sensor.so">
      <ros>
        <namespace>/robot</namespace>
        <remapping>~/out:=scan</remapping>
      </ros>
      <output_type>sensor_msgs/LaserScan</output_type>
      <frame_name>lidar_link</frame_name>
    </plugin>
  </sensor>
</gazebo>
```

### 6. Model Validation

Validate URDF models:

```bash
# Check URDF syntax
check_urdf robot.urdf

# Process Xacro and check
xacro robot.urdf.xacro > robot.urdf && check_urdf robot.urdf

# Visualize URDF tree
urdf_to_graphviz robot.urdf

# View in RViz
ros2 launch urdf_tutorial display.launch.py model:=robot.urdf.xacro

# Convert URDF to SDF
gz sdf -p robot.urdf > robot.sdf
```

### 7. SDF Format

Generate SDF for Gazebo:

```xml
<?xml version='1.0'?>
<sdf version='1.7'>
  <model name='my_robot'>
    <link name='base_link'>
      <inertial>
        <mass>10.0</mass>
        <inertia>
          <ixx>0.0833</ixx>
          <iyy>0.2167</iyy>
          <izz>0.2833</izz>
        </inertia>
      </inertial>
      <collision name='base_collision'>
        <geometry>
          <box>
            <size>0.5 0.3 0.1</size>
          </box>
        </geometry>
        <surface>
          <friction>
            <ode>
              <mu>1.0</mu>
              <mu2>1.0</mu2>
            </ode>
          </friction>
        </surface>
      </collision>
      <visual name='base_visual'>
        <geometry>
          <box>
            <size>0.5 0.3 0.1</size>
          </box>
        </geometry>
        <material>
          <ambient>0.0 0.0 0.8 1</ambient>
        </material>
      </visual>
    </link>
  </model>
</sdf>
```

## MCP Server Integration

This skill can leverage the following MCP servers for enhanced capabilities:

| Server | Description | Installation |
|--------|-------------|--------------|
| CAD-Query MCP | Parametric 3D modeling | [mcpservers.org](https://mcpservers.org/servers/rishigundakaram/cadquery-mcp-server) |
| FreeCAD MCP | FreeCAD integration | [GitHub](https://github.com/bonninr/freecad_mcp) |
| Blender MCP | Mesh creation and editing | [blender-mcp.com](https://blender-mcp.com/) |
| OpenSCAD MCP | Parametric modeling | [playbooks.com](https://playbooks.com/mcp/jhacksman-openscad) |

## Best Practices

1. **Consistent units** - Use SI units (meters, kilograms, radians)
2. **Origin placement** - Place link origins at center of mass when possible
3. **Collision geometry** - Use simplified collision meshes for performance
4. **Inertia accuracy** - Calculate accurate inertia for stable simulation
5. **Mesh optimization** - Reduce polygon count for collision meshes
6. **Modular design** - Use Xacro macros for reusable components

## Process Integration

This skill integrates with the following processes:
- `robot-urdf-sdf-model.js` - Primary model creation process
- `robot-system-design.js` - System architecture with models
- `moveit-manipulation-planning.js` - MoveIt configuration
- `gazebo-simulation-setup.js` - Simulation model setup

## Output Format

When executing operations, provide structured output:

```json
{
  "operation": "create-urdf",
  "robotName": "my_robot",
  "status": "success",
  "validation": {
    "syntaxValid": true,
    "inertiasValid": true,
    "jointsValid": true
  },
  "artifacts": [
    "urdf/my_robot.urdf.xacro",
    "meshes/base_link.stl",
    "meshes/wheel.stl"
  ],
  "statistics": {
    "links": 5,
    "joints": 4,
    "sensors": 2
  }
}
```

## Constraints

- Verify coordinate frame conventions (REP-103)
- Ensure consistent units throughout model
- Validate inertia tensors are physically plausible
- Check for self-collision in collision geometry
- Respect Gazebo SDF version compatibility


---
Source attribution: a5c-ai
Original project: https://github.com/a5c-ai/babysitter
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Gabriel Moreira

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: a5c-ai
Original project: https://github.com/a5c-ai/babysitter
Attribution basis: Upstream repository explicitly recorded in package mirror path

Fields of work: Development & Engineering
Roles: Backend Developer, ML / AI Engineer
Specialties: API
Tools: Ros
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: fe2465d632b152f19f837354501020d825888fa9e6ac50c0d037724a5f0f9467