add ros parameters file to node context

[Karsten1987]

fixes #59

With this PR, the actual parameters are being set:

 ➭ ros2 param list
...
/controller_manager:
  joint_state_controller.type
  joint_trajectory_controller.type
  update_rate
  use_sim_time

While implementing this, I found actually a second bug in which all specified controllers in the loaded yaml file would be loaded. It didn't show in the example, however this would necessarily lead to resource conflicts when more than one controller use the same command interface.

[ahcorde]

@Karsten1987 I was testing your contribution but I was not able to run the example or get the /joint_states. You didn't launch the controllers.

[Karsten1987]

You didn't launch the controllers.

That's on purpose. As mentioned above, not all controllers can be loaded/configured at the same time due to resource conflicts. Also I believe it's not good practice to launch them within the gazebo plugin. I'd rather use either the spawner functionality (once available) or load them explicitly via services through a launch file.

[ahcorde]

I will have a look to the PR ros-controls/ros2_control#310

anyhow the conditional to get the udpate_rate is required.

[Karsten1987]

you don't necessarily need the spawner PR. You should be able to use ros2 control load_start_controller in the launch file to start the controllers.

Not sure we need to manually parse the parameters to get the update_rate. We should be able to extract that parameter via a get_parameter call to controller manager.

[Karsten1987]

anyhow the conditional to get the udpate_rate is required.

done in 1047c22

[ahcorde]

@Karsten1987

I was testing the ros2 control commands. I was able to start the joint_state_controller

ros2 control load_start_controller joint_trajectory_controller` 

But I'm not able to load the joint_trajectory_controller. Digging about what it's happening here. The /joint_trajectory_controller parameters are not set.

ros2 param get /joint_trajectory_controller  joints
String values are: []

You should set up the parameters for the controller in the code.

[Karsten1987]

There's currently no clear way to set parameters to a gazebo plugin's node. So I had to do this manually by parsing the ros parameter's file and add the arguments to the node's context. That's certainly not a recommended way, but the only feasible at the moment.

/cc @chapulina @jacobperron

[joshnewans]

I just wanted to add my 2c and say that as someone fairly new to all this, I found it quite confusing that the plugin loaded my controllers on its own as I expected a flow similar to my real robot where I used ros2 control load_start_controller xxx. The new behaviour resulting from this PR seemed more intuitive to me.

This PR resolved an issue I was having where the controller_manager and its child controllers did not obey the use_sim_time parameter I specified in the yaml file (and as I understand it there is currently no way to globally enable use_sim_time).

[Karsten1987]

@ahcorde friendly ping.

[ahcorde]

I created a PR which builds on top of this PR load the controllers in the launch files: #64