第 11 節

Gazebo simulation platform

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Briefly describe

Gazebo is currently divided into two main versions.

One is the older Gazebo Classic, and the other is the newer Ignition Gazebo (Gazebo Fortress).

In this post, Gazebo refers to Gazebo Classic, while Ignition Gazebo will be distinguished accordingly.

Now ROS2 Humble comes with Ignition Gazebo (Gazebo Fortress), but ROS2 Jazzy comes with Gazebo Harmonic. It is recommended to learn Gazebo Harmonic!

Scene

In ROS robot development, physical robots offer the advantages of directness and realism, but they also have some drawbacks, such as:

  1. High cost: Developing an autonomous mobile robot requires purchasing expensive hardware components such as sensors, motors, and controllers. Moreover, these components may need frequent replacement or upgrades during the early stages of development, leading to a sharp increase in costs.
  2. Resource Constraints: Due to limited funding and resources, it may not be possible to simultaneously have multiple physical robots for testing. This can extend the testing cycle and hinder research and development progress.
  3. Environmental uncertainty and complexity: When testing robots in real-world environments, various unpredictable situations may arise, such as changes in lighting, uneven terrain, electromagnetic interference, etc. These factors can all affect the robot's performance.
  4. Safety Risks: During testing, if the robot's control algorithm or hardware malfunctions, it may cause the robot to lose control, potentially harming people or the environment.

In the field of ROS robot development, simulation technology is widely used to compensate for the limitations of testing with physical robots.

Concept

Robot simulation is a process that uses computer models and simulation technology to mimic the behavior and performance of robots in a virtual environment. It involves creating virtual robot and environment models to simulate the robot's perception, control, and motion capabilities, as well as its interactions with the environment and other objects.

Purpose

Through simulation testing, the cost and risk of robot development can be reduced, the performance and reliability of robot systems can be improved, and reference and guidance can be provided for actual robot deployment.

Simulation Advantages:

Simulation plays a pivotal role in the research and development of robotic systems. Compared to physical robot implementation, simulation offers the following significant advantages during development and testing:

  1. Low cost: Current robot costs remain prohibitively high, often reaching hundreds of thousands, and simulation can significantly reduce costs and minimize risk.
  2. Efficient: The setup environment is more diverse and flexible, which can improve testing efficiency and test coverage.
  3. High Security: In the simulation environment, there is no need to worry about wear and tear.

Simulation technology provides developers with a comprehensive testing and verification platform that is both efficient and safe, as well as low-cost.

Simulation Defects:

Robots perform quite differently in simulation environments compared to real-world settings. In other words, simulation cannot fully replicate the real physical world, and there are some cases of "distortion." Reasons:

  1. The physics engine used by the simulator is currently unable to fully and accurately simulate the physical conditions of the real world.
  2. The simulator constructs an absolutely ideal scenario for joint actuators (motors and gearboxes), sensors, and signal communication. It currently does not support simulating actual hardware defects or certain edge-case conditions.

In short, while simulation technology is important, it cannot fully replace physical testing. Physical testing can verify the accuracy of simulation results and uncover issues that simulations might overlook.

## Chapter Summary

This chapter mainly introduces the application of the 2D simulation tool stage_ros2 and the 3D simulation tool Ignition Gazebo in ROS2.

The relevant knowledge points are as follows:

  • Theoretical knowledge of simulation;
  • Using stage_ros2 in ROS2;
  • Using Ignition Gazebo in ROS2.

Through the content above, we introduced the application scenarios and concepts of simulation in ROS2, as well as its advantages and disadvantages compared to physical robots. We also learned how to set up simulation environments and simulate robots using stage_ros2 and Ignition Gazebo, laying the foundation for further study.

Additionally, besides stage_ros2 and Ignition Gazebo, there are several other software options available for ROS2 simulation. Below are some common choices:

  • Webots: Webots is a powerful open-source multi-robot simulation software platform that supports simulation of various robot hardware and sensors, and can be integrated with ROS 2.
  • Gazebo Classic: Gazebo Classic is a commonly used simulator in ROS 1, and it can also be connected to and used via ROS 2.
  • MORSE: MORSE is an open-source simulator based on Python, used for ROS 2 simulation and robot development, supporting a variety of sensor and behavior models.
  • V-REP: V-REP is a powerful multi-robot simulation platform that supports communication with ROS 2, enabling the simulation of various robot models and scenarios.

These are some common ROS 2 simulation software packages. You can choose the appropriate one based on your specific needs for simulation and development. Please note that some simulators may require adaptation and configuration to be compatible with ROS 2.

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