ENME480 · Wiki

ROS 2 in this course

You do not install ROS 2. It is already in the course Docker image.

Do not follow a ROS 2 installation guide

Every ROS 2 tutorial online starts by telling you to install ROS 2 Humble on Ubuntu. Skip that. Installing ROS 2 on your own machine on top of the course image gives you two copies that shadow each other, and the symptoms are miserable to debug — packages that exist but will not import, nodes that cannot see each other, sourcing that silently picks the wrong one.

Everything you need is inside the container. If a guide says sudo apt install ros-humble-desktop, you are on the wrong page.

Where ROS 2 comes from

The image built in Ubuntu Setup is based on osrf/ros:humble-desktop and already contains:


ROS 2	Humble Hawksbill, full desktop install
Build tools	`colcon`, `rosdep`, `vcstool`
Simulation	Gazebo (GZ), `ros_gz` bridge, `turtlesim`
GUI tools	`rqt` and its plugins, `rviz2`
Robot drivers	Universal Robots driver and UR3e MoveIt config
Extras	`tf_transformations`, `usb-cam`, MoveIt

So your job is to get into the container, not to install anything.

Getting in

Covered in Ubuntu Setup, and again in Week 3, Part C. Short version:

cd ~
bash startDocker.sh        # start it once
bash connectToDocker.sh    # every additional terminal

Your prompt changes when you are inside.

The container is deleted every time you exit

It runs with --rm. Anything you install or create inside is gone when you type exit — sudo apt install included.

Two directories survive, because they are shared with your own machine:

~/ENME480_mrc/src     <-->  ~/enme480_ws/src
~/ENME480_mrc/config  <-->  ~/enme480_ws/config

Put your work there and nowhere else.

Checking ROS 2 works

Inside the container:

ros2 topic list

You should see /parameter_events and /rosout. That is ROS 2 running.

For a fuller check, in two terminals:

ros2 run demo_nodes_cpp talker      # terminal 1
ros2 run demo_nodes_cpp listener    # terminal 2

The listener should print what the talker sends.

To check graphical programs can reach your screen, which is the thing most likely to be broken:

rqt

If no window appears, see the troubleshooting section in Ubuntu Setup.

Your workspace

It already exists, at ~/enme480_ws. Do not create one.

This matters: the official ROS 2 tutorials have you build a workspace at ~/ros2_ws, which is outside the shared folders above. Work there and it is destroyed when the container shuts down, with no warning.

cd ~/enme480_ws
colcon build --symlink-install
source install/setup.bash

--symlink-install links to your Python files rather than copying them, so editing a node does not need a rebuild. You only need colcon build again after adding a file or changing setup.py.

Sourcing

Handled for you. The image writes this into ~/.bashrc, so every new terminal sources ROS 2 and your workspace automatically.

One exception worth remembering: a terminal opened before a colcon build does not know about anything built since. Either open a new terminal or run:

source ~/enme480_ws/install/setup.bash

Package not found immediately after a successful build is almost always this.

Command reference

Looking at a running system

ros2 node list                  # what is running
ros2 topic list                 # what topics exist
ros2 topic echo /topic_name     # watch messages go past
ros2 topic info /topic_name     # message type, publisher and subscriber counts
ros2 topic hz /topic_name       # publishing rate
ros2 interface show <msg type>  # the fields inside a message

ros2 topic info is the one to reach for when two nodes will not talk. A mismatched topic name throws no error — the nodes just never find each other. If a count is 0 when you expect 1, you have a name or type mismatch, or something is not running.

Running things

ros2 run <package> <executable>
ros2 launch <package> <launch file>
ros2 pkg executables <package>      # what a package can run

Parameters and services

ros2 param list
ros2 param get /node_name parameter_name
ros2 service list
ros2 service call /service_name <service type> "data"

Graphical tools

Tool	What it is for
`rqt`	Plugin GUI. Node Graph and Topic Monitor are the useful ones
`rviz2`	3D visualisation of robot state and sensor data

Learning ROS 2

The official beginner tutorials are mirrored on this site, so you can read them without being sent to a guide whose paths do not match our setup:

ROS 2 Tutorials

Start with Writing a simple publisher and subscriber. It explains every line of a talker node, which is the pattern nearly everything in this course is built from.

Read them for the concepts. Ignore the parts that create a workspace or a package — you already have both.

Getting help

Official docs: docs.ros.org/en/humble
ROS Answers: answers.ros.org
Piazza, office hours, and lab sessions for anything course-specific