ROS 2 Lyrical Luth · Lesson 85 of 86

Building a multi-robot fleet

Project: several namespaced robots with shared map, fleet manager and traffic rules.

Estimated time · 120–180 min

Learning goals

What you will understand

Explain building a multi-robot fleet in your own words
Use it in a small robotics example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

A fleet project combines everything: each robot runs a full stack in its own namespace, all share the same map, a fleet manager assigns tasks, and a traffic layer reserves corridors. Generate the launch actions for N robots in a Python loop so the number of robots is just an argument.

Give each robot a unique start pose, TF frame prefix or namespaced TF, and Nav2 parameters with the namespace substituted. Test with two robots first, then scale up while watching CPU, DDS traffic and planning times. Record a bag per robot with the same start time.

Guided lesson

Work through these steps

1.
Source the ROS 2 Lyrical environment in a fresh terminal.
2.
Read the building a multi-robot fleet example and identify what each line does.
3.
Build only the affected package, source the workspace overlay, and run the example.
4.
Inspect the result from a second terminal with the ros2 CLI or RViz2 and compare it with the expected result.

Worked example

Read it before you run it

from launch import LaunchDescription
# Launch container.
def generate_launch_description():
# Entry point.
    robots = [{'name': f'robot{i}', 'x': 2.0 * i, 'y': 0.0} for i in range(3)]
# Three robots, two metres apart.
    actions = [robot_group(r['name'], r['x'], r['y']) for r in robots]
# One launch group per robot (defined elsewhere).
    return LaunchDescription(actions)
# Start the whole fleet.

What the example is doing

1.The ros2 commands query the running graph; they do not prove that a node's internal behavior is correct.
2.Build from the workspace root, then source install/setup.bash so the shell can discover the new package.
3.Use a second sourced terminal to inspect nodes and interfaces while the example runs.

Watch it run · Mobile robot

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Copy the starter into your ROS 2 package, replace every TODO, then build with colcon build and run it from a sourced terminal.

def generate_launch_description():
    # TODO: build three robots with names robot0..robot2 and x = 2.0 * i using a list comprehension
    return LaunchDescription([])

Expected output

Three robots start at different positions

Stuck? Show the full solution (try it yourself first)

def generate_launch_description():
    robots = [{'name': f'robot{i}', 'x': 2.0 * i, 'y': 0.0} for i in range(3)]
    return LaunchDescription([])

Expected result

How you know it worked

ROS_DISTRO is lyrical in every terminal used for the exercise.
The complete package from the exercise builds and the expected graph entity appears in a second terminal.

Practical exercise

Apply the lesson

Launch three simulated robots with the same map and separate namespaces, send each a goal, add the reservation table for the central corridor, and report any conflicts before and after.

Before you continue

ROS_DISTRO reports lyrical in every terminal you used
The example builds and runs without errors
You checked the result with a ros2 command, RViz2 or a test, not just by reading the code

If something goes wrong

ros2 cannot find a package or executable.

Source /opt/ros/lyrical/setup.bash, build from the workspace root, then source install/setup.bash in that terminal.

Nodes run but cannot discover each other.

Confirm both terminals use Lyrical, the same ROS_DOMAIN_ID, and compatible network/discovery settings.