Add a passthrough_controller demo

[AndyZe]

This is a simple demo of a chained controller that I'm working on with @saikishor

[codecov-commenter]

Codecov Report

Merging #556 (19eed91) into master (e7f9962) will increase coverage by 0.75%.
The diff coverage is 34.91%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@            Coverage Diff             @@
##           master     #556      +/-   ##
==========================================
+ Coverage   35.78%   36.53%   +0.75%     
==========================================
  Files         189        7     -182     
  Lines       17570      676   -16894     
  Branches    11592      357   -11235     
==========================================
- Hits         6287      247    -6040     
+ Misses        994      134     -860     
+ Partials    10289      295    -9994     

Flag	Coverage Δ
unittests	36.53% <34.91%> (+0.75%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ontroller/test/test_load_diff_drive_controller.cpp	11.11% <0.00%> (ø)
diff_drive_controller/src/odometry.cpp	42.16% <11.11%> (ø)
diff_drive_controller/src/speed_limiter.cpp	46.55% <11.11%> (ø)
...ive_controller/test/test_diff_drive_controller.cpp	17.62% <12.08%> (ø)
...iff_drive_controller/src/diff_drive_controller.cpp	47.09% <46.88%> (ø)
...de/diff_drive_controller/diff_drive_controller.hpp	100.00% <100.00%> (ø)
...troller/include/diff_drive_controller/odometry.hpp	100.00% <100.00%> (ø)

... and 189 files with indirect coverage changes

[bmagyar]

@christophfroehlich @ARK3r do you guys think this'd be better hosted in the demos repo?

[ARK3r]

I honestly don't know enough about use cases for this, but I think it could be useful to demonstrate how to write a custom controller perhaps.

[saikishor]

I honestly don't know enough about use cases for this, but I think it could be useful to demonstrate how to write a custom controller perhaps.

Hello @ARK3r,

With @AndyZe, we wrote this controller in order to have it as a tutorial/demo on how to write a chainable controller. This is a simple controller that simply takes the interface and forwards the interface to another controller. It is purely written for demonstration.

As we always have the controller name prepended to the exported interfaces, as in the interface /controller_1/position_x will be exposed as /passthrough_controller/controller_1/position_x, I don't think we will have a lot of use cases with this. In the future, we might modify it to expose it without the initial controller naming, then it might be useful.

[christophfroehlich]

In this case I vote for the demo repository. I also proposed a GPIO controller there, where the use-case is kind of similar to this one (demonstration only).

[saikishor]

Perfect!. We will then open a PR to the demos repository soon.
Thank you.

[christophfroehlich]

@saikishor there is an existing PR for a chained controller example: ros-controls/ros2_control_demos#162

Will your contribution replace it (and work without any adaptions of upstream packages)?

[saikishor]

@christophfroehlich Thanks for the reference to an existing example.

As far as I understand, that example PR shows how to launch and setup the controller chaining for an existing set of controllers, but there is no clear example of how to write a simple one (I'm aware of the existing admittance controller), but it is very complex for a newbie. This controller itself will serve as a simple example. I think this controller is kinda similar to the #318 's (chainable_forward_controller)

[olivier-stasse]

I agree with @saikishor . Receiving the same kind of comments often, I am willing to help on the simple example.

[christophfroehlich]

@saikishor Ok, I understand. Nevertheless, I think a self-contained example including how to write a chained controller, as well as how to configure the chain, would be most valuable. This would be then a merge of this one and the existing one from @destogl

[saikishor]

@christophfroehlich Sounds good to me, then If I understood correctly, I will have to move this controller to the ros-controls/ros2_control_demos and maybe I can pick @destogl's commits and add changes on the top?.

I believe all these changes should go inside the example_10 folder structure right?

BTW, I am currently working on the controllers sorting, once I am done with that I will be happy to contribute to this.

[christophfroehlich]

We have a PR for example_10 and example_11 already, so your's would be example_12 then 😉
I suggest having a look on the existing PR but make a new one directly to the master branch, otherwise we have to approve/merge it twice. And pls follow the folder structure of the master branch.

[saikishor]

@christophfroehlich Sure. Thanks for the info. 👍

[saikishor]

Hello @AndyZe!

You can close this PR, I've moved this example controller into the ros2_control_demos repo under example_12.

Thank you,

Best Regards,
Sai