URDF Class: Introduction to Robot Modelling (Robotics Arm)

The video is a recording of a class session titled "Application of ROS2 in Robotic Arms," where the speaker aims to teach the practical application of ROS 2 concepts to actual robotic arms, moving beyond the simplified stick-like models used previously.

Change in Approach and Task Overview
The speaker notes that the approach for this class will be different, moving from concept and math to application.
The previous task, Task 3, involved a two-link robot arm using a simplified, stick-like mechanism.
The current goal is to apply learned concepts to an actual robot, like the very popular Kuka KR 14-4, which is not just "all sticks" and requires more complex functionality.
The goal is to answer the question, "How do we now apply all what we've been learning through the actual robotic arm?".
The Scenario: ROS 2 Integration
The speaker paints a scenario where a company has designed a mechanical robot and needs ROS 2 integration.
The mechanical design provides the physical parts, but software (like ROS) is needed to drive the motors and control the movement of joints and grippers.
The class will work with three versions of popular robotic company parts, drawing from CAD repositories online. Companies mentioned include Fanuc, Kuka, Unit3 (or "Universal Robots"), and others.
The ROS Integration Process

The speaker outlines the steps for ROS integration:
Robot Description Layer: This is the first step and the foundation of everything.
The CAD files are provided (not regular SolidWorks files).
Convert CAD to Meshes: CAD files must be converted into meshes (STL or DAE formats) because meshes are simpler formats that represent the CAD in a series of connected triangles.
Use URDF: The key to describing the robot to the computer is the Unified Robot Description Format (URDF). URDF is an XML format that defines the robot by combining everything the PC needs to know about it.
URDF defines links (robot parts), joints (connections), origins, limits, inertia, collision, and visual elements.
Visualization: The immediate goal is to use the URDF to visualize the robot in RViz (Arvis).
Advanced Topics: Other integration steps that are currently advanced and will be discussed later include:
Motion planning (which includes kinematics).
Path planning, motion execution, and collision checking.
Control, which involves deriving, coding, and tuning the governing equations of the system.
Hardware integration (sim-to-real), which involves testing simulation solutions on the actual hardware.
Practical Task 4 Guide (Live Coding/Instruction)

The speaker begins outlining Task 4, which is both the lecture and the assignment. The task involves assembling a given robot's parts using URDF to match the expected final result.
Get the Files: Clone the repository (the speaker corrects this to "fork and then clone" the repository).
Tools: Tools for inspecting the mesh files (STL or DAE) include SolidWorks, Fusion 360, or the free, open-source MeshLab. Instructions for installing MeshLab are provided.
Setup the Workspace:
Create a new folder outside the cloned repository, for example, "Tax 4 submission".
Copy the assigned robot's folder into this new folder.
Create a ROS 2 package using the command: ros2 package create package_name --build-type ament_cmake. The speaker recommends naming the package with the convention of robot_name_description.
Inside the new package folder, create a new folder called meshes.
Copy the STL or DAE files from the initial robot folder into the meshes folder.
Create a folder called URDF in the package folder.
Writing the URDF:
Install extensions like ROS for syntax highlighting and autocompletion.
Create a file inside the URDF folder (e.g., dog.urdf).
The Robot Tag: All code must be enclosed within a single robot tag.
The Link Tag: The next step is to define the links and determine the base link. Each link needs three definitions: visual, collision, and inertia.