ros2_control controller template package [WIP]

[jellehierck]

Hi!

For my group it was useful to have a package template for ros2_control controllers. I have started implementation of this to create a controller package and showcase some useful tricks, which became super simple with ros2-pkg-create!

I created this draft PR to let you know I am working on this and give updates on the progress. I am also curious if you would be interested to merge this alongside the other templates.

The controller which is generated is a joint impedance controller meant for a Franka FR3 robot, a 7-DoF robotic arm. The controller will take in a position reference and generate a torque output based on stiffness and damping parameters.

I currently have implemented:

• Generation of a ros2_control controller including dependencies and a load test.
• Generation of a launch and config file structures to easily include the controller into other projects.
• Generation of real-time safe subscriber for reference commands from a topic (when the use_subscriber flag is used).
  • I did not yet implement the non-subscriber controller.
• Generation of real-time safe publisher to output information to a topic (when the use_publisher flag is used).
  • I did not yet implement the non-publisher controller.
• Generation of an additional custom controller messages package for the subscriber and/or publisher.
  • This additional interfaces package is always generated, should only be done if use_subscriber and/or use_publisher are set.
  • Or, alternatively, I could alter the control algorithm used to take in common_interfaces such as geometry_msgs/msg/Twist and geometry_msgs/msg/Wrench. But I decided to stick with joint impedance for now since that is a lot simpler to implement 😉.

And I also have some more stuff planned:

• Update documentation with:
  • Examples of how to start the controller and use its features.
  • Examples of how to include the launch file(s) into other projects.
• Integrating an action server to control the robot, similar to Nav2.
• Upgrading to semantic components for hardware access instead of directly accessing the joint command interfaces.

Some stuff I am not sure about because of time constraints (any help would be super welcome 😄):

• It would be nice to have a general robot URDF instead of relying on the franka_description package, but I did not look for a generally available robot description package. Also, it would require quite some refactoring of the code.
• I did not look into the docker integration yet.

Let me know what you think!