adding low cost robot arm (koch v1.1) URDF

[pweids]

I wanted to use the Koch v1.1 URDF in projects with LeRobot and Rerun, which can ingest URDFs. I saw it was in awesome-robot-descriptions, but not here. So I just brought it into here.

I tested it by running directly:

>>> from robot_descriptions.loaders.yourdfpy import load_robot_description
>>> robot = load_robot_description("low_cost_robot_arm_description")
>>> robot.joint_names
['joint_1', 'joint_2', 'joint_3', 'joint_4', 'joint_5', 'joint_6']

(tox had a lot of unrelated failures that I didn't want to wade through for a small addition like this)

[coveralls]

Pull Request Test Coverage Report for Build 16225737099

Details

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.009%) to 98.105%

---

Totals
Change from base Build 16225601439:	0.009%
Covered Lines:	1191
Relevant Lines:	1214

---

💛 - Coveralls

[stephane-caron]

Thank you for starting this PR 👍 It looks like the description does not load successfully in PyBullet:

   b3Warning[examples/Importers/ImportURDFDemo/BulletUrdfImporter.cpp,126]:
  No inertial data for link, using mass=1, localinertiadiagonal = 1,1,1, identity local inertial frameb3Warning[examples/Importers/ImportURDFDemo/BulletUrdfImporter.cpp,126]:
  ...
  ======================================================================
  ERROR: test_low_cost_robot_arm_description (test_pybullet.TestPyBullet)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/home/runner/work/robot_descriptions.py/robot_descriptions.py/tests/loaders/test_pybullet.py", line 54, in test
      load_robot_description(description)
    File "/home/runner/work/robot_descriptions.py/robot_descriptions.py/.tox/loader-pybullet/lib/python3.9/site-packages/robot_descriptions/loaders/pybullet.py", line 50, in load_robot_description
      robot = pybullet.loadURDF(module.URDF_PATH, **kwargs)
  pybullet.error: Cannot load URDF file.

Does it happen as well if you try to load it in PyBullet on your machine?

[pweids]

unfortunately not. Looks like it's an issue with the URDF upstream. The error I get is:

b3Printf: /Users/paul/.cache/robot_descriptions/koch_description/simulation/follower.urdf:27: cannot find 'follower/meshes/base_link.STL' in any directory in urdf path

The URDF asks for filename="package://follower/meshes/base_link.STL"

But the URDF looks like directory looks like:

.
└── simulation
    ├── follower.urdf
    └── meshes
        ├── base_link_motor.STL
        ├── base_link.STL
        ├── link_1_motor.STL
        ├── link_1.STL
        ├── link_2_motor.STL
        ├── link_2.STL
        ├── link_3_motor.STL
        ├── link_3.STL
        ├── link_4_motor.STL
        ├── link_4.STL
        ├── link_5_motor.STL
        ├── link_5.STL
        └── link_6.STL

Odd that it works with yourdfpy, but not pybullet. Not sure where to go from here