Multi-Body Dynamics Preprocessor

A desktop application for preparing CAD assemblies for multi-body dynamics simulations. Load STEP files, define rigid bodies, create joints, and export to simulation-ready formats. Here is a demo :

https://www.linkedin.com/posts/utkarsh-kulkarni-737a21143_python-mbd-simulation-activity-7417465950595358720-Bytp?utm_source=share&utm_medium=member_desktop&rcm=ACoAACLbVNsBFxFMNDgH9pOH3QkAD194cmSTt6s

Features

• STEP File Import: Load CAD assemblies from STEP files and automatically extract individual bodies
• 3D Visualization: Interactive 3D viewer with pan, zoom, rotate, and selection capabilities
• Physics Properties: Automatic calculation of volume, center of mass, and inertia tensors
• Joint Creation: Define joints between bodies by selecting faces, edges, or vertices
  • Supported joint types: Fixed, Revolute (Hinge), Prismatic, Cylindrical, Spherical, Universal, Planar
• Forces & Torques: Add external forces and torques to bodies
• Motors: Attach motors to joints with position, velocity, or torque control
• Export: Export assembly data to JSON format for use in dynamics solvers

Installation

Prerequisites

• Python 3.8 or higher
• Conda (recommended for pythonocc-core)

Setup

1. Clone the repository:

   git clone https://github.com/utk11/MBD-PreProcessor.git
   cd MBD-PreProcessor

2. Create a conda environment and install pythonocc-core:

   conda create -n mbd python=3.10
   conda activate mbd
   conda install -c conda-forge pythonocc-core

3. Install remaining dependencies:

   pip install -r requirements.txt

Usage

Run the application:

python main.py

Basic Workflow

1. File → Open STEP: Load a CAD assembly file
2. Select bodies in the left panel tree view
3. Create joints via Edit → Create Joint:
   • Select joint type
   • Pick two bodies
   • Select geometry (face/edge) on each body to define joint frames
4. Add forces/torques if needed
5. File → Export: Save to JSON for your dynamics solver

Project Structure

├── main.py                 # Application entry point
├── core/                   # Core logic
│   ├── data_structures.py  # RigidBody, Joint, Frame classes
│   ├── step_parser.py      # STEP file loading
│   ├── geometry_utils.py   # Mesh and hull calculations
│   └── physics_calculator.py
├── gui/                    # User interface
│   ├── viewer_3d.py        # 3D viewport
│   ├── body_tree_widget.py # Body/joint tree panel
│   ├── property_panel.py   # Properties editor
│   └── *_dialog.py         # Creation dialogs
├── visualization/          # Rendering
│   └── *_renderer.py       # Body, joint, force renderers
├── export/                 # Export functionality
│   └── exporter.py         # JSON export
└── tests/                  # Unit tests

Export Format

The exported JSON includes:

• Bodies: Volume, center of mass, inertia tensor, collision hull vertices
• Joints: Type, connected bodies, joint frames in local and global coordinates
• Forces/Torques: Magnitude, direction, application point
• Motors: Control type, target values

Dependencies

• pythonocc-core - CAD kernel (OpenCASCADE wrapper)
• PySide6 - GUI framework
• NumPy - Numerical computing
• SciPy - Convex hull generation
• trimesh - Mesh operations

Contributing

Contributions are welcome! Please feel free to submit issues and pull requests.

License

This project is licensed under the GPL-3.0 License - see the LICENSE file for details.