Docs/fix robot system launch path

[flippybit]

Hi @ipa-cmh and @ipa-vsp
Here is my 1st real PR. 😅

The fix is to solve issue #182
a FileNotFoundError when following the humble user-guide "How to create a robot system" readthedocs

The user guide references the robot_control_launch.py file which expects the robot_controller.urdf.xacro file at a certain path.
However, this path does not align with the location where the canopen_tests package actually keeps it:
canopen_tests/urdf/robot_controller/robot_controller.urdf.xacro

I apologize if I've overlooked any GitHub best practices. Thank you for your understanding in advance.

[ipa-vsp]

Hi @flippybit,

I have merged your changes from branch docs/fix_robot_system_launch_path into PR #176 to prevent conflicts with the master branch.

Thanks for your review!

[flippybit]

Hi @ipa-vsp ,

I knew i did something wrong when i saw all the confilicts i followed some guide were i needed to open a branch for making a pull request.
Anyways i think i have found another discrepancy in the docs.
Should i share my findings opening a new issue ? || do i just post it here ?

thnx !

[ipa-vsp]

Hi @flippybit,

You can post it here.

Thank you!

[flippybit]

ros2 humble guide "How to create a robot system with ros2_control"

I think i have found 2 minor discrepencies in the "How to create a robot system with ros2_control" Point 12:

(Using the ros2 humble guide readthedocs)

1 There is no such topic name /joint1/forward_position_controller

CLICK TO EXPAND.

In the docs point 12

It states:
You can now control the robot with the forward_command_controller.
You can as well visualize the robot in rviz by adding a tf or a robot_model and setting the fixed frame to base_link

You can move the robot with the following command:

ros2 topic pub /joint1/forward_position_controller/command std_msgs/msg/Float64 "data: [1.0, 1.0]"

But this gives the following error output:

Failed to populate field: Value '[1.0, 1.0]' is expected to be a dictionary but is a list

My investigations/probings

1 There is not such topic named /joint1/forward_position_controller

If you run

$ ros2 topic list

You get the following topics:

/clicked_point
/dynamic_joint_states
/forward_position_controller/commands  <-- I THINK THIS IS THE TOPIC WE WANT TO PUBLISH TO
/forward_position_controller/transition_event
/goal_pose
/initialpose
/joint_1/joint_states
/joint_1/nmt_state
/joint_1/rpdo
/joint_1/tpdo
/joint_2/joint_states
/joint_2/nmt_state
/joint_2/rpdo
/joint_2/tpdo
/joint_state_broadcaster/transition_event
/joint_states
/parameter_events
/robot_description
/rosout
/slave_node_1/transition_event
/slave_node_2/transition_event
/tf
/tf_static

If you ask ROS2 for more info about /forward_position_controller/commands

$ ros2 topic info /forward_position_controller/commands 
Type: std_msgs/msg/Float64MultiArray
Publisher count: 0
Subscription count: 1

Proposed solution

publish to the /forward_position_controller/commands

ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data: [1.0, 1.0]"

This outputs:

ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data: [1.0, 1.0]"
publisher: beginning loop
publishing #1: std_msgs.msg.Float64MultiArray(layout=std_msgs.msg.MultiArrayLayout(dim=[], data_offset=0), data=[1.0, 1.0])

publishing #2: std_msgs.msg.Float64MultiArray(layout=std_msgs.msg.MultiArrayLayout(dim=[], data_offset=0), data=[1.0, 1.0])

publishing #3: std_msgs.msg.Float64MultiArray(layout=std_msgs.msg.MultiArrayLayout(dim=[], data_offset=0), data=[1.0, 1.0])

2 There is no base_link in the /robot_description

In the docs it tells you to visualize the movement of the joints using rivz2:

In the docs it states:
" You can as well visualize the robot in rviz by adding a tf or a robot model and setting the fixed frame to base_link:"

CLICK TO EXPAND.

If you run:

ros2 run tf2_tools view_frames

You get the following transform tree with NO base_link

Proposed solution

1. Run rviz2

ros2 run rviz2 rviz2 

2. Configure rviz2

1. Add a robot model
   Select as a Description Source Topic
   Select as Description Topic /robot_description

2. In Global Options
   Set Fixed Frame as World

3. Visualize the cilinder move like magic

ros2 topic pub /forward_position_controller/commands std_msgs/msg/Float64MultiArray "data: [1.0, 1.0]"

Hope it helped someone!

[destogl]

@Xi-HHHM can you please check this?

[ipa-vsp]

Continue #283