ENME480 · Wiki

Gazebo in this course

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

Do not run sudo apt install gazebo

That installs Gazebo Classic (gazebo11), which is a different, older simulator from the one this course uses. Installing it gives you two simulators fighting over the same ROS topics and model paths, and the failures are confusing — worlds that will not load, plugins that are not found, robots that appear but do not move.

The image ships Gazebo (GZ, formerly Ignition) with the ros_gz bridge. That is what every lab uses.

What the image gives you

Installed as part of the course image, nothing for you to add:


Simulator	Gazebo (GZ), launched as `ign gazebo`
ROS 2 bridge	`ros_gz_bridge`, `ros_gz_image`, `ros_gz_sim`
Robot	Universal Robots description and UR3e MoveIt config
Course packages	`enme480_gazebo`, `ur3e_mrc_sim` (from the course repo)

Checking it runs

Inside the container:

ign gazebo

A window should open with a list of example worlds. That is the whole check — close it again.

If no window appears, the problem is the container reaching your display, not Gazebo. See the troubleshooting section in Ubuntu Setup, and confirm you started the container with the right compose file for your machine.

Launching the course simulation

You will not write your own world files. The labs use prepared launch files. From Week 6 onward, in separate terminals or tmux panes:

# the UR3e in Gazebo
ros2 launch enme480_gazebo enme480_ur3e_empty.launch.py

# the simulated robot's control interface
ros2 launch ur3e_mrc_sim ur3e_enme480.launch.py

# the ENME480 command layer
ros2 launch ur3e_enme480 ur3e_sim_enme480.launch.py

Then commands go to the robot over a topic, exactly as they do on the real arm:

ros2 topic pub --once /ur3e/command ur3e_mrc_msgs/msg/CommandUR3e "destination: [0, -1.57, -1.57, 0, 0, 0]
v: 1.0
a: 1.0
io_0: false"

The point of the simulator in this course is that the same topic interface drives the real UR3e. Code that works in Gazebo should work on the arm, which is why we develop in simulation first.

Use tmux for the panes

The image has tmux configured. tmux to start, Ctrl+A b to split horizontally, Ctrl+A v to split vertically. Much easier than juggling four connectToDocker.sh terminals.

Driving the GUI

Camera

Action	Control
Orbit	Left click and drag
Pan	Middle click and drag, or Shift + left drag
Zoom	Scroll wheel
Look at a model	Double click it

Simulation

Action	Control
Play / pause	Buttons at the bottom left
Step one frame	Step button, while paused
Reset	World menu, Reset

Pausing is genuinely useful. If a robot is moving unexpectedly, pause and step through rather than trying to read a blur.

Troubleshooting

No window opens. The container cannot reach your display. This is the same problem rqt has, and it is covered in Ubuntu Setup. Check you used the right compose file for your machine (NVIDIA or standard).

Very slow, or a black window. Usually software rendering because the GPU is not available to the container. On a machine with an NVIDIA GPU, confirm you did the NVIDIA step in Ubuntu Setup. In a VM it will be slow regardless — reduce the window size and expect low frame rates.

The robot appears but does not move. The simulator is running but the control layer is not. Check all three launch files above are up, then:

ros2 topic list
ros2 topic info /ur3e/command

If the publisher or subscriber count is 0, one of the launch files is not running or died on startup. Read its terminal.

A launch file is not found. Your workspace is not sourced, or the package is not built:

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

Remember that a terminal opened before a build does not know about it.

Getting help

Gazebo docs: gazebosim.org/docs
ros_gz: github.com/gazebosim/ros_gz
Piazza, office hours, and lab sessions for anything course-specific