Setup with ign_ros2_control

[sjahr]

Hi @AndrejOrsula,
this repository is a very useful example for combining ros2 and ignition, thank you for this great work! You mentioned in ign_ros2_control#1 that you successfully launched a robot with ros2_control in Gazebo Ignition. I've tried to get a Panda running but I was not able to successfully do it so far and wanted to ask if it is possible for you to share your setup?
Thanks a lot in advance!

[AndrejOrsula]

Hello @sjahr,

Unfortunately, I do not have a setup available at the moment. However, I am planning to create ign_ros2_control config for Franka Emika Panda relatively soon. It will be in the coming weeks, but I don't exactly know when I will have free time for it because it requires some refactoring to replace the current hacky setup.

I will also try to update the examples in this repository to use ign_ros2_control and deprecate the current approach using JointTrajectoryController Ignition plugin (I'll keep it in a separate branch in case someone ever needs it).

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For now, feel free to post below a specific issue/problem that is blocking you. I will try to provide some answers if I know.

[sjahr]

Sounds great! Thanks for your quick reply. I'll share my blocker later with you. Let me know when you need a review/help with your work.

[AndrejOrsula]

@sjahr Yesterday, I added the basic support for Franka Emika Panda as a part of AndrejOrsula/panda_ign_moveit2#7. Ignition Gazebo example can be launched with ex_ign_control.launch.py. You can change what command interface(s) to use by modifying ex_ign_control.launch.py#L56. If you want to try it, use ex_fake_control.launch.py to make sure the rest of the system works.

Video of effort-control is below (fingers are oscillating because PIDs are not tuned).

panda_ign_moveit2_effort_control_v0.mp4

There are still several issues, namely:

• Created new issue | In the default joint configuration that the robot is spawned in ([0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]), the robot has one of the joints outside of its position limits and there is a self-collision of hand with one of the lower links.
  • I do not know any good way to spawn model into Gazebo with a specific non-default configuration. It can be done programatically through joint position reset though.
  • For now, I increased the default tolerance and disabled collision geometry for arm in the example.
• Documented in README | [external issue (ros2_controllers)] For pure effort-control, you need to use [JTC] Implement effort-only command interface ros-controls/ros2_controllers#225. In both position and velocity mode, the commands otherwise bypass the physics engine.
• Tuned a little bit and created a new issue | For effort-control, the PID gains require more tuning. I normally use large joint damping and friction so that I can reduce simulation step_size really low without the robot becoming unstable. Thus, these parameters also need to be tuned more.
• [external issue (ign_ros2_control)] For effort-control, joint controllers seem to kick in only after sending the first command (the robot flops at the beginning).
• No longer an issue | Xacro selection of command interface (e.g. panda.ros2_control#L40-L47) does not seem to be robust enough. It sometimes does not function properly. I am not sure what causes it to fail, maybe it's just some local issue I am having.

There might be others too. These are just the ones I noticed so far.

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One more thing I would like to add into launch files:

• Created new issue | Use xacro to generate also SDF before spawning it into Gazebo. This would enable passing of xacro arguments directly to SDF model from launch CLI. I already have a setup for it in a simple Python script, but I have not tried integrating it with any launch.py yet.

[sjahr]

Awesome thank you! I'll test it and give you feedback

[AndrejOrsula]

The following point from the comment above is actually not an issue at all, it works all the time. One just must remember to update model.sdf when trying new command_interface (e.g. use scripts/xacro2sdf.bash). This is due to the controller parameters that are passed to the ignition_ros2_control::IgnitionROS2ControlPlugin plugin.

• Xacro selection of command interface (e.g. panda.ros2_control#L40-L47) does not seem to be robust enough. It sometimes does not function properly. I am not sure what causes it to fail, maybe it's just some local issue I am having.

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This won't be an issue once the following is added.

• Use xacro to generate also SDF before spawning it into Gazebo. This would enable passing of xacro arguments directly to SDF model from launch CLI. I already have a setup for it in a simple Python script, but I have not tried integrating it with any launch.py yet.

[AndrejOrsula]

The following PRs are now merged in.

• pymoveit2 pymoveit2#1
• Convert repository to support ign_ros2_control panda_ign_moveit2#7
• Convert repository into examples for MoveIt 2 with ign_ros2_control #12

Some of the aforementioned points that are not yet fixed were converted into issues.