General approach representing a complete system using URDF/XACRO?
I'm new to ROS, but would like to represent a complete basic robotic system that involves a 4DOF arm, 2 test fixtures and a test piece that the arm picks up and moves from one fixture to the other. In SolidWorks I have separate parts for the test fixtures and test piece. I also have vendor provided parts and an assembly for the robotic arm. I created a complete assembly with all of those items and mated them as appropriate. I also set the mates for the arm joints and I can move the arm to see all the correct motions that are supported.
I've tried the URDF exporter for Solidworks and read many of the guides on this site which are helpful. What's unclear to me is how to approach this from a URDF/XACRO perspective? What should be my base_link in this case? I think it could be the base of the robot arm (one part within that arm assembly) or the table (which is not modeled yet)? This seems to matter because link relationships with the other components are then defined. Would it make more sense to create separate urdf exports for each of these 4 components (robot arm, fixture 1 and 2 and the test piece)? If so, would i use XACRO for any of this? The goal is to simulate and test the robotic application knowing that components of the system might change over time.
Just as a comment: it's not an active REP yet, but in an attempt to provide some guidance on frame names and structure, I've written Coordinate Frames for Serial Industrial Manipulators. Note that it say "industrial" in there, but that's a bit too restrictive. See gavanderhoorn/rep#3 for some discussion (it's not perfect of course).
As to some examples of how to put workcells together (as I guess that's sort of what you're asking), you could see whether the ROS-Industrial Training Exercises can provide some. Specifically exercises
3.0and3.1. Again: this will not be perfect, but shows some ways of modelling these kinds of environments.