Multi robot support

[roni-kreinin]

Description

Alternative to #189, but using GroupAction and PushRosNamespace for a cleaner implementation.
I am also proposing that the namespace is the robot name, and by default all robots will have to be namespaced for consistency, even with just 1 robot. The default robot name and therefore namespace is create3.

Launch files updates (ignition):

• ignition.launch.py: Launches just Gazebo without spawning a robot
• create3_spawn.launch.py: Spawns a robot. Requires that ignition.launch.py has been launched first.
• create3_ignition.launch.py: Default launch file to launch ignition.launch.py with a default create3 robot.

Other changes:

• cmd_vel:
  • In ignition, /<namespace>/cmd_vel is now the topic being bridged to the equivalent /<namespace>/cmd_vel ros topic.
  • Default cmd_vel topic for teleop plugin is now /create3/cmd_vel.
• Create3 buttons:
  • Ignition topic is now /model/<namespace>/create3_buttons. ROS topic is now /<namespace>/_create3_buttons. Its hidden so that it is not confused with interface_buttons.
• Using ros_gz_bridge instead of ros_ign_bridge. The ign version was not being terminated properly when the simulation was closed, leaving stray nodes running in the background.
• Created individual bridges for each lidar. Supposed to increase performance. See Performance issues with bridging gpu_lidar data gazebosim/ros_gz#368
• Added static transforms from tf_prefixed odom and base_link frames to namespaced frames. See [DiffDriveController] Optional tf namespace prefixes instead of using node namespace ros-controls/ros2_controllers#533
• Spawning dock correctly when the y and yaw values are changed.
• Open a namespaced RViz window for each robot

TODO:

• Fix docking status
• Update RViz config
• Add the same changes to classic gazebo
• Get Context and Namespace Handling for Multi-Robot Sim ros-controls/gz_ros2_control#92 merged and released.

Notes:

• Spawning 2 robots works, but spawning a 3rd causes a libGL segfault for me. Not sure if this is a hardware limitation.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.
Provide instructions so we can reproduce. Also list any relevant details for your test configuration.

# Default single robot launch
ros2 launch irobot_create_ignition_bringup create3_ignition.launch.py

# Spawn a second robot
ros2 launch irobot_create_ignition_bringup create3_spawn.launch.py namespace:=robot2 y:=1.0

Alternatively:

# Launch ignition
ros2 launch irobot_create_ignition_bringup ignition.launch.py

# Spawn robot 1
ros2 launch irobot_create_ignition_bringup create3_spawn.launch.py namespace:=robot1 

# Spawn robot 2
ros2 launch irobot_create_ignition_bringup create3_spawn.launch.py namespace:=robot2 y:=1.0

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation

[alsora]

I'm not convinced by forcing a namespace even when running with a single robot.
One of the most frequent request for support that we receive is due to users setting a namespace on the robot and then not pre-pending it to their other commands.

[roni-kreinin]

@alsora That's fair. What about having a namespace arg that defaults to robot_name, and in create3_ignition.launch.py we set robot_name to create3 and namespace to empty by default? That way the default launch remains the same but any additional calls to create3_spawn.launch.py will apply a namespace automatically.

[alsora]

I'm not sure I understand why we need both namespace and robot name arguments (I still need to finish looking at the PR).

I would imagine that we could do this only with the namespace argument. This would be empty by default.
If users want to manually spawn multiple robots they would just do something like

ros2 launch irobot_create_ignition_bringup create3_spawn.launch.py namespace:=robot1 
ros2 launch irobot_create_ignition_bringup create3_spawn.launch.py namespace:=robot2

A dedicated multi-robot launch file could be used such as

ros2 launch irobot_create_ignition_bringup multirobot_spawn.launch.py num_robots:=5 namespace_prefix:=robot

[roni-kreinin]

The robot name is used mostly for the model name in ignition. We could just namespace the create3 name and call each robot <namespace>/create3.

As for the multi-robot launch file, I would suggest we make a .yaml file to pass in. Something like:

robot1:
    x: 1.0
    y: 1.2
    z: 0.0
    yaw: 0.0
robot2:
    x: 2.0
    y: 0.0
    z: 0.0
    yaw: 1.5707

Then you can just call

ros2 launch irobot_create_ignition_bringup multirobot_spawn.launch.py robots:=/path/to/robots.yaml

[sp-sophia-labs]

Happy to support and contribute on this code if it proves to be the better approach. @roni-kreinin I see that you pushed something similar to us in turtlebot4_simulator as well, looks like we are trying to achieve the same things. Can we work together?

[roni-kreinin]

@sp-sophia-labs Of course. Feel free to make PR's against https://github.com/roni-kreinin/create3_sim/tree/multi_robot. Most of this PR is based on your work, I just wanted to make it compatible with the way that Nav2 and the physical TurtleBot 4 robot handle namespacing.

[roni-kreinin]

@alsora I have updated it to use just the namespace. The robot model will now be <namespace>/create3, and the dock model is <namespace>/standard_dock.

The default create3_ignition.launch.py spawns a single robot at the world origin without a namespace. Additional robots can be spawned with

ros2 launch irobot_create_ignition_bringup create3_spawn.launch.py namespace:=robot1 x:=1.0

I tried making a multi robot launch file but ran into a couple of issues:

• Spawning two models at the same time at launch causes an ignition rendering segfault
• Nested IncludeLaunchDescription calls don't seem to apply the unique namespace arguments correctly. They require a top level declaration of the arg, and that one gets used for all included launch descriptions. I think this is just a limitation of ros2 launch, unless you know a way around it.

Currently the only way I can get multiple robots working is to launch each one in a separate terminal.

[roni-kreinin]

Looking to create a new default world to improve performance. The depot world is very GPU intensive which causes performance issues once the robot is spawned as well.

[alsora]

@roni-kreinin can you add support for gazebo classic and documentation in the readme on how to use namespaces?

[alsora]

Thank you for addressing the requests and sorry for this taking so long!

[icsl-Jeon]

That is why I could not spawn two robots with different namespaces at the same time with a single launch..
Were you able to find the way for this?
Thank you in advance ;)

[alsora]

@icsl-Jeon the readme file contains instructions for spawning multiple robots with different namespaces (https://github.com/iRobotEducation/create3_sim#namespacing).
This requires to call multiple launch files, or to write your own launch script that combines them

[icsl-Jeon]

Of course I tried the instruction.
What I am interested in was having a single launch file that spawns the multiple robots.
I could not succeed as this mentioned:
#207 (comment)

[alsora]

We don't provide such a launch file, but there's nothing inherently preventing to do it.

If you need help please open a separate ticket and provide us with details about your launch script and the errors/problems.