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Joint Tutorial needs topic_name in SDF examples. #2629

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Joint Tutorial needs topic_name in SDF examples. #2629

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89 changes: 45 additions & 44 deletions tutorials/joint_controller.md
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Original file line number Diff line number Diff line change
Expand Up @@ -166,10 +166,10 @@ This is how the model will look:

```xml
<plugin
filename="gz-sim-joint-controller-system"
name="gz::sim::systems::JointController">
<joint_name>j1</joint_name>
<initial_velocity>1.0</initial_velocity>
filename="gz-sim-joint-controller-system"
name="gz::sim::systems::JointController">
<joint_name>j1</joint_name>
<initial_velocity>1.0</initial_velocity>
</plugin>
```

Expand Down Expand Up @@ -203,12 +203,13 @@ Replace the velocity mode plugin mentioned above with the following lines in the

```xml
<plugin
filename="gz-sim-joint-controller-system"
name="gz::sim::systems::JointController">
<joint_name>j1</joint_name>
<use_force_commands>true</use_force_commands>
<p_gain>0.2</p_gain>
<i_gain>0.01</i_gain>
filename="gz-sim-joint-controller-system"
name="gz::sim::systems::JointController">
<joint_name>j1</joint_name>
<use_force_commands>true</use_force_commands>
<p_gain>0.2</p_gain>
<i_gain>0.01</i_gain>
<topic>topic_name</topic>
</plugin>
```

Expand Down Expand Up @@ -309,17 +310,17 @@ For this let's use the previously discussed SDF file.

```xml
<plugin
filename="gz-sim-joint-position-controller-system"
name="gz::sim::systems::JointPositionController">
<joint_name>j1</joint_name>
<topic>topic_name</topic>
<p_gain>1</p_gain>
<i_gain>0.1</i_gain>
<d_gain>0.01</d_gain>
<i_max>1</i_max>
<i_min>-1</i_min>
<cmd_max>1000</cmd_max>
<cmd_min>-1000</cmd_min>
filename="gz-sim-joint-position-controller-system"
name="gz::sim::systems::JointPositionController">
<joint_name>j1</joint_name>
<topic>topic_name</topic>
<p_gain>1</p_gain>
<i_gain>0.1</i_gain>
<d_gain>0.01</d_gain>
<i_max>1</i_max>
<i_min>-1</i_min>
<cmd_max>1000</cmd_max>
<cmd_min>-1000</cmd_min>
</plugin>
```

Expand Down Expand Up @@ -591,28 +592,28 @@ This is how the model will look:
Append the following lines before `</model>` tag in the SDF file.

```xml
<plugin
filename="gz-sim-joint-trajectory-controller-system"
name="gz::sim::systems::JointTrajectoryController">
<joint_name>RR_position_control_joint1</joint_name>
<initial_position>0.7854</initial_position>
<position_p_gain>20</position_p_gain>
<position_i_gain>0.4</position_i_gain>
<position_d_gain>1.0</position_d_gain>
<position_i_min>-1</position_i_min>
<position_i_max>1</position_i_max>
<position_cmd_min>-20</position_cmd_min>
<position_cmd_max>20</position_cmd_max>

<joint_name>RR_position_control_joint2</joint_name>
<initial_position>-1.5708</initial_position>
<position_p_gain>10</position_p_gain>
<position_i_gain>0.2</position_i_gain>
<position_d_gain>0.5</position_d_gain>
<position_i_min>-1</position_i_min>
<position_i_max>1</position_i_max>
<position_cmd_min>-10</position_cmd_min>
<position_cmd_max>10</position_cmd_max>
<plugin
filename="gz-sim-joint-trajectory-controller-system"
name="gz::sim::systems::JointTrajectoryController">
<joint_name>RR_position_control_joint1</joint_name>
<initial_position>0.7854</initial_position>
<position_p_gain>20</position_p_gain>
<position_i_gain>0.4</position_i_gain>
<position_d_gain>1.0</position_d_gain>
<position_i_min>-1</position_i_min>
<position_i_max>1</position_i_max>
<position_cmd_min>-20</position_cmd_min>
<position_cmd_max>20</position_cmd_max>
<topic>topic_name</topic>
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So what's the behavior without <topic> specified? Can we make sure that scenario works as well?

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Sure you would need to pass it to the default topic instead. Is that preferred? Or just want it duplicated in that portion?

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I guess my question is, has the default topic changed? I ask because #2546 changed some default topics for some systems and those systems had to be updated.

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No, the default topic I don't believe has changed, the tutorial shows to publish this to control it:

gz-sim/tutorials/joint_controller.md

Line 622 in 76305df

gz topic -t "topic_name" -m gz.msgs.JointTrajectory -p '

Note that you need to have the topic name match that topic or it won't work.

And then it says to echo:

gz-sim/tutorials/joint_controller.md

Line 670 in 76305df

gz topic -e -t "/model/RR_position_control/joint_trajectory_progress"

Which once again if you change it to listen to published topic won't work. So one or the other needs to be changed/fixed to work.

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So @azeey do you want an example with only the default topic, only the "assigned topic" or one with both?

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@caguero caguero Nov 18, 2024 •
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@azeey , any final decision/comments here?

<joint_name>RR_position_control_joint2</joint_name>
<initial_position>-1.5708</initial_position>
<position_p_gain>10</position_p_gain>
<position_i_gain>0.2</position_i_gain>
<position_d_gain>0.5</position_d_gain>
<position_i_min>-1</position_i_min>
<position_i_max>1</position_i_max>
<position_cmd_min>-10</position_cmd_min>
<position_cmd_max>10</position_cmd_max>
</plugin>
```

Expand Down Expand Up @@ -667,7 +668,7 @@ In case, PID gains are not specified then by default force mode will work.
4) Checking the progress of the commanded trajectory.

```bash
gz topic -e -t "/model/RR_position_control/joint_trajectory_progress"
gz topic -e -t "/topic_name_progress"
```

This returns the progress of the commanded trajectory which is a value between (0,1].
Expand Down
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