Halfcar Downhill Simulation

A comprehensive simulation framework for longitudinal two-dimensional dynamics of a half-car/full-bicycle model with unilateral contact constraints, featuring customizable downhill courses and detailed animations.

Overview

This repository provides two implementations of a sophisticated halfcar dynamics simulation:

• MATLAB - Original implementation with extensive testing
• Python - Complete port with identical functionality

The simulation models a bicycle/motorcycle descending various downhill terrains with realistic physics including suspension dynamics, tire contact mechanics, and aerodynamic forces.

Key Features

• 5-DOF Halfcar Model - Longitudinal dynamics with pitch, heave, and wheel hop
• Unilateral Contact Constraints - Realistic tire-road interaction
• Customizable Courses - Build complex downhill tracks from modular segments
• Advanced Physics - Suspension damping, aerodynamic drag, rolling resistance
• Real-time Animation - Detailed visualization of vehicle dynamics
• Power Pacing - Realistic propulsive force modeling

Course Generation

Create custom downhill courses by assembling predefined segments in CourseLibrary.m (MATLAB) or course_library.py (Python):

• Bumpy sections - Random terrain variations
• Jumps and drops - Airborne dynamics
• Staircases - Step-like obstacles
• Gap jumps - Discontinuous terrain
• Rock gardens - High-frequency roughness
• Root sections - Natural trail features
• Curves - Banking and camber effects

Quick Start

MATLAB

% Run the main simulation
Main_downhill

% Select course and parameters
[course, info] = SelectCourse('extreme');

Python

# Install dependencies
pip install -r python/requirements.txt

# Run simulation
cd python
python main.py

Repository Structure

halfcar/
├── matlab/              # MATLAB implementation
│   ├── Main_downhill.m     # Main simulation script
│   ├── ComputeAccelerations.m  # Physics engine
│   ├── ConstructCourse.m      # Course generation
│   ├── animate_results.m      # Animation system
│   └── ...                   # Supporting functions
└── python/              # Python implementation
    ├── main.py              # Main simulation script
    ├── params.py            # Model parameters
    ├── physics/             # Physics and dynamics
    ├── road/                # Course generation
    ├── viz/                 # Visualization
    ├── sim/                 # Integration
    └── post/                # Post-processing

Physics Model

The simulation implements a 5-degree-of-freedom halfcar model:

• Chassis dynamics - X, Y translation and pitch rotation
• Suspension systems - Front and rear wheel hop
• Contact mechanics - Point and circle contact models
• Force modeling - Gravity, suspension, tire, aerodynamic, and propulsive forces

Requirements

MATLAB

• MATLAB R2019b or later
• Optimization Toolbox (for ODE integration)

Python

• Python 3.8+
• NumPy, SciPy, Matplotlib
• See python/requirements.txt for complete list

Development Status

• MATLAB: Fully tested and validated
• Python: Complete port with identical functionality
• Documentation: Comprehensive inline comments
• Animation: High-quality real-time visualization

Contributing

This is a research/educational project. Feel free to:

• Report issues or bugs
• Suggest improvements
• Fork for your own modifications

License

This project is open source. Please cite appropriately if used in academic work.

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Originally developed in MATLAB, then ported to Python for broader accessibility.