Module 2: The Digital Twin (Gazebo & Unity)
Learning Objectives
- Understand the concept of digital twins in robotics
- Learn about physics simulation in Gazebo
- Master 3D rendering and visualization in Unity
- Implement sensor simulation for realistic perception
- Integrate simulation environments with ROS 2
Overview
This module introduces the concept of digital twins in robotics, focusing on two primary simulation environments: Gazebo for physics-based simulation and Unity for high-fidelity rendering. Digital twins enable safe testing of robotic algorithms in virtual environments before deployment to real hardware.
Content
A digital twin is a virtual representation of a physical robot or system that allows for testing, validation, and optimization without risk to actual hardware. In robotics, digital twins are crucial for:
- Safety: Testing dangerous scenarios without physical risk
- Cost Reduction: Validating algorithms before hardware investment
- Development Acceleration: Faster iteration cycles than physical testing
- Training: Developing perception and control algorithms with synthetic data
Digital Twin Architecture
Physical Robot ──────────────────────────────── Virtual Robot (Digital Twin)
│ │
│ ┌─────────────────────────────────────┐ │ ┌─────────────────────┐
│ │ Sensors │ │ │ Simulation Engine │
│ │ ┌─────────┐ ┌─────────┐ ┌─────┐ │ │ │ │
│ │ │Camera │ │LiDAR │ │IMU │ │ │ │ ┌─────────────┐ │
│ │ └─────────┘ └─────────┘ └─────┘ │ │ │ │ Gazebo │ │
│ └─────────────────────────────────────┘ │ │ │ Physics │ │
│ │ │ │ │ │ │ Engine │ │
│ ▼ ▼ ▼ │ │ └─────────────┘ │
│ ┌─────────────────────────────────────┐ │ │ ┌─────────────┐ │
│ │ Data Processing │ │ │ │ Unity │ │
│ │ │ │ │ │ Rendering │ │
│ │ Perception ─▶ Planning ─▶ Control │ │ │ │ Engine │ │
│ └─────────────────────────────────────┘ │ │ └─────────────┘ │
│ │ │ │ │ │ │
└─────────┼───────────┼───────────┼───────────────┘ └─────────────────────┘
│ │ │
┌──────▼────┐ ┌────▼────┐ ┌────▼────┐
│ Control │ │ Planning│ │Perception│
│ Commands │ │ Actions │ │ Data │
└───────────┘ └─────────┘ └──────────┘
The two primary simulation approaches in robotics are:
- Physics Simulation (Gazebo): Focuses on accurate physics modeling and sensor simulation
- Visual Simulation (Unity): Emphasizes high-fidelity rendering and human-robot interaction
Simulation Environment Architecture
┌─────────────────────────────────────────────────────────────────┐
│ Simulation Environment │
│ ┌─────────────────┐ ┌─────────────────┐ ┌─────────────┐ │
│ │ Robot Model │ │ Environment │ │ Sensors │ │
│ │ │ │ │ │ │ │
│ │ ┌─────────────┐ │ │ ┌─────────────┐ │ │ ┌─────────┐ │ │
│ │ │ URDF/SDF │ │ │ │ 3D Scenes │ │ │ │ Cameras │ │ │
│ │ │ Description │ │ │ │ & Maps │ │ │ │ & LiDAR│ │ │
│ │ └─────────────┘ │ │ └─────────────┘ │ │ └─────────┘ │ │
│ └─────────────────┘ └─────────────────┘ └─────────────┘ │
│ │ │ │
│ ▼ ▼ │
│ ┌─────────────────────────────────────────┐ │
│ │ Physics Engine │ │
│ │ │ │
│ │ • Collision Detection │ │
│ │ • Dynamics Simulation │ │
│ │ • Force/Torque Computation │ │
│ └─────────────────────────────────────────┘ │
│ │ │
│ ▼ │
│ ┌─────────────────────────────────────────┐ │
│ │ Rendering Engine │ │
│ │ │ │
│ │ • 3D Visualization │ │
│ │ • Real-time Rendering │ │
│ │ • Sensor Simulation │ │
│ └─────────────────────────────────────────┘ │
└─────────────────────────────────────────────────────────────────┘
Course Timeline Mapping
This module covers approximately 2-3 weeks of instruction in a 13-week course:
- Weeks 6-7: Gazebo simulation, URDF/SDF, Unity visualization
- Includes hands-on labs with both simulation environments
Exercises
Exercise 1: Basic Gazebo Simulation
Create a simple robot model and simulate it in Gazebo:
- Import a basic robot model into Gazebo
- Configure physics properties and collision detection
- Implement basic movement and control
- Observe the robot's behavior in the simulated environment
Exercise 2: Unity Environment Setup
Set up a Unity environment for robot simulation:
- Create a basic scene with terrain and obstacles
- Import robot models and configure physics
- Implement basic camera controls for observation
- Export the environment for ROS integration
Exercise 3: Sensor Simulation Integration
Connect sensor simulation to your robot:
- Add virtual sensors (LiDAR, cameras, IMU) to your robot model
- Configure sensor parameters to match real hardware
- Integrate sensor data with ROS 2 topics
- Validate sensor data accuracy and timing
Assessment Project
Module 2 Assessment: Digital Twin Implementation
Students will create a complete digital twin of a simple mobile robot:
- Design the robot in URDF with appropriate physical properties
- Create both Gazebo and Unity simulation environments
- Implement sensor simulation with realistic noise models
- Demonstrate robot navigation in both environments
- Compare performance between simulation and theoretical expectations
Requirements:
- Robot model with at least 3 sensor types
- Working navigation in both simulation environments
- Documentation of simulation parameters and validation
- Video demonstration of robot behavior
Summary
This module covered the fundamentals of digital twin technology in robotics, including both physics-based simulation in Gazebo and high-fidelity rendering in Unity. Students now understand how to create virtual representations of physical robots for safe testing and development. The integration of these simulation environments with ROS 2 enables comprehensive testing of robotic algorithms before deployment to real hardware.
Accessibility Features
This module includes the following accessibility features:
- Semantic HTML structure with proper heading hierarchy (H1, H2, H3)
- Sufficient color contrast for text and background
- Clear navigation structure with logical tab order
- Alternative text for code examples and diagrams
- Descriptive headings and section titles
- Keyboard navigable interactive elements