Running the Gazebo Simulation

This tutorial provides the basic commands needed to run the Perseus rover in Gazebo simulation.

Prerequisites

Nix package manager installed
Perseus v2 repository cloned locally
Basic familiarity with command line interface

Steps

1. Enter the Simulation Environment

nix develop .#simulation

This command enters the specialised Nix development shell configured for simulation with all necessary dependencies.

2. Navigate to the ROS Workspace

cd software/ros_ws

3. Build the Workspace

colcon build

This builds all ROS2 packages in the workspace, including the simulation components.

4. Source the Workspace

source install/setup.bash

This sets up the ROS2 environment variables to use the built packages.

5. Launch the Simulation

ros2 launch perseus_simulation perseus_sim.launch.py

This command launches the Gazebo simulation with the Perseus rover model.

:::{warning} Some simulation environments (e.g. worlds with falling rock obstacles) use external assets hosted online.

An active internet connection may be required on first launch to download these assets.
Once downloaded, assets are typically cached locally by the simulator and can be reused offline.
If you experience missing models or world load failures, please ensure you are connected to the internet and restart the simulator.

Future work may migrate these assets to local storage to fully support offline simulation. :::

6. Activate the Drive Controller

After the simulation has fully started, you need to activate the drive controller. In a separate terminal, run:

nix develop .#simulation
cd software/ros_ws
source install/setup.bash
ros2 control set_controller_state diff_drive_base_controller active

This step is required to enable the rover's wheel movement in simulation.

Controlling the Rover

Once the simulation is running and the controller is active, you can control the rover using keyboard input. In a separate terminal, run:

nix develop .#simulation
cd software/ros_ws
source install/setup.bash
ros2 run teleop_twist_keyboard teleop_twist_keyboard --ros-args -r /cmd_vel:=/cmd_vel_out -p stamped:=true

Troubleshooting

Rover Not Moving in Teleop

If the rover doesn't respond to keyboard commands:

Workaround for broken ROS controller:

There is a bug being investigated where the ROS2 controller daemon is non-responsive.

Instead of activating the controller with ros2 control set_controller_state diff_drive_base_controller active use:

ros2 service call /controller_manager/switch_controller controller_manager_msgs/srv/SwitchController "{activate_controllers: ['diff_drive_base_controller'], deactivate_controllers: [], strictness: 1, activate_asap: false, timeout: {sec: 5, nanosec: 0}}"

This sets the state directly.

Check if the controller is active:

ros2 control list_controllers

You should see diff_drive_base_controller as active. If it shows inactive, run:

ros2 control set_controller_state diff_drive_base_controller active

Verify topic connections:

ros2 topic info /cmd_vel_out

This should show both publishers and subscribers.

Test topic communication:
```
ros2 topic echo /cmd_vel_out
```
You should see messages when pressing keys in the teleop terminal.

:::

The first time you run the simulation, Gazebo may download the lunar landscape model, which can take up to 20 minutes
Ensure you have an internet connection for the initial setup
If the system has a firewall, the network must be set to trusted to download assets needed for the simulation
The simulation requires significant system resources and may perform better with hardware acceleration
If the rover doesn't move, make sure the drive controller is activated (step 6)

:::