How to Create URDF from CAD Software

Overview

This document explains how to create a URDF file from SolidWorks models by using:

1. SolidWorks to URDF Exporter

2. scikit-robot’s convert-urdf-mesh command

• SolidWorks to URDF Exporter This exporter helps convert SolidWorks assemblies into a format (3dxml) which is more easily processed to produce URDF-compatible mesh files.

• scikit-robot ``convert-urdf-mesh`` A tool within the scikit-robot library that can convert 3D model files (like .3dxml, .obj, .stl, etc.) into a URDF or mesh files (e.g., .dae) suitable for ROS.

Coordinate Systems

• .3dxml export: uses the overall assembly coordinate system from SolidWorks.

• .stl export: uses each part’s or link’s local coordinate system.

convert-urdf-mesh provides an option for adjusting coordinates:

• --force-zero-origin: Forces the origin to be the link’s local coordinate in the converted mesh files (e.g., .dae). - Useful when your source is in the assembly coordinate system (like .3dxml). - Highly recommended if you plan to use these meshes in MuJoCo.

Installation

1. Install scikit-robot

pip install scikit-robot

or clone directly from GitHub if you need the latest updates:

git clone https://github.com/iory/scikit-robot.git
cd scikit-robot
pip install -e .

2. Install SolidWorks URDF Exporter

• Obtain the plugin from the following link:

  SolidWorks URDF Exporter Plugin

• Follow the official instructions to install it into your SolidWorks environment.

  Installation Instructions

Workflow

1. Export from SolidWorks

   • In SolidWorks, open your assembly.

   • Use the “SolidWorks to URDF Exporter” plugin to generate a .3dxml file.

2. Convert to DAE (or STL) and Generate URDF

   • Run the scikit-robot command to convert .3dxml (or other mesh formats) to .dae and generate a URDF automatically.

   • Example usage:

   convert-urdf-mesh <URDF_PATH> --output <OUTPUT_URDF_PATH>
   

   • This command outputs: - A set of mesh files (e.g., .dae) - A URDF file referencing those meshes

3. Verify URDF in ROS

   • Copy the generated URDF and mesh files into your ROS package.

   • Test in Rviz or another ROS-compatible viewer:

   roslaunch urdf_tutorial display.launch model:=path/to/generated.urdf
   

   • Confirm the model loads and displays properly.

4. Usage with MuJoCo

   • MuJoCo typically requires meshes to be centered at their local origin.

   • Therefore, always use the --force-zero-origin option when converting to ensure proper alignment.

   convert-urdf-mesh <URDF_PATH> --output <OUTPUT_URDF_PATH> --force-zero-origin