# Multi-Vehicle Simulation with Gazebo

This topic explains how to simulate multiple UAV vehicles using Gazebo (Gz) and SITL.

Note

Multi-Vehicle Simulation with Gazebo is only supported on Linux.

Gazebo makes it very easy to setup multi-vehicle scenarios (compared to other simulators).

First build PX4 SITL code using:

make px4_sitl

Each instance of PX4 can then be launched in its own terminal, specifying a unique instance number and its desired combination of environment variables:

ARGS ./build/px4_sitl_default/bin/px4 [-i <instance>]

<instance>: The instance number of the vehicle.
- Each vehicle must have a unique instance number. If not given, the instance number defaults to zero.
- When used with PX4_GZ_MODEL, Gazebo will automatically pick a unique model name in the form ${PX4_GZ_MODEL}_instance.
ARGS: A list of environmental variables, as described in Gazebo Simulation > Usage/Configuration Options.

This allows for greater flexibility and customization.

# Multiple Vehicles with ROS 2 and Gazebo

Multiple vehicles with ROS 2 are possible.

First follow the installation instructions for Gazebo.
Then configure your system for ROS 2 / PX4 operations.

In different terminals manually start a multi vehicle simulation. This example spawns 2 X500 Quadrotors and a fixed-wing:

PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4 -i 1

PX4_SYS_AUTOSTART=4001 PX4_GZ_MODEL_POSE="0,1" PX4_GZ_MODEL=x500 ./build/px4_sitl_default/bin/px4 -i 2

PX4_SYS_AUTOSTART=4004 PX4_GZ_MODEL_POSE="0,2" PX4_GZ_MODEL=rc_cessna ./build/px4_sitl_default/bin/px4 -i 3

Start the agent:
```
MicroXRCEAgent udp4 -p 8888
```
The agent will automatically connect to all clients.
Run ros2 topic list to see the topic list, which should look like this:

/parameter_events
/px4_1/fmu/in/obstacle_distance
/px4_1/fmu/in/offboard_control_mode
/px4_1/fmu/in/onboard_computer_status
/px4_1/fmu/in/sensor_optical_flow
/px4_1/fmu/in/telemetry_status
/px4_1/fmu/in/trajectory_setpoint
/px4_1/fmu/in/vehicle_attitude_setpoint
/px4_1/fmu/in/vehicle_command
/px4_1/fmu/in/vehicle_mocap_odometry
/px4_1/fmu/in/vehicle_rates_setpoint
/px4_1/fmu/in/vehicle_trajectory_bezier
/px4_1/fmu/in/vehicle_trajectory_waypoint
/px4_1/fmu/in/vehicle_visual_odometry
/px4_1/fmu/out/failsafe_flags
/px4_1/fmu/out/sensor_combined
/px4_1/fmu/out/timesync_status
/px4_1/fmu/out/vehicle_attitude
/px4_1/fmu/out/vehicle_control_mode
/px4_1/fmu/out/vehicle_global_position
/px4_1/fmu/out/vehicle_gps_position
/px4_1/fmu/out/vehicle_local_position
/px4_1/fmu/out/vehicle_odometry
/px4_1/fmu/out/vehicle_status
/px4_2/fmu/in/obstacle_distance
/px4_2/fmu/in/offboard_control_mode
/px4_2/fmu/in/onboard_computer_status
/px4_2/fmu/in/sensor_optical_flow
/px4_2/fmu/in/telemetry_status
/px4_2/fmu/in/trajectory_setpoint
/px4_2/fmu/in/vehicle_attitude_setpoint
/px4_2/fmu/in/vehicle_command
/px4_2/fmu/in/vehicle_mocap_odometry
/px4_2/fmu/in/vehicle_rates_setpoint
/px4_2/fmu/in/vehicle_trajectory_bezier
/px4_2/fmu/in/vehicle_trajectory_waypoint
/px4_2/fmu/in/vehicle_visual_odometry
/px4_2/fmu/out/failsafe_flags
/px4_2/fmu/out/sensor_combined
/px4_2/fmu/out/timesync_status
/px4_2/fmu/out/vehicle_attitude
/px4_2/fmu/out/vehicle_control_mode
/px4_2/fmu/out/vehicle_global_position
/px4_2/fmu/out/vehicle_gps_position
/px4_2/fmu/out/vehicle_local_position
/px4_2/fmu/out/vehicle_odometry
/px4_2/fmu/out/vehicle_status
/px4_3/fmu/in/obstacle_distance
/px4_3/fmu/in/offboard_control_mode
/px4_3/fmu/in/onboard_computer_status
/px4_3/fmu/in/sensor_optical_flow
/px4_3/fmu/in/telemetry_status
/px4_3/fmu/in/trajectory_setpoint
/px4_3/fmu/in/vehicle_attitude_setpoint
/px4_3/fmu/in/vehicle_command
/px4_3/fmu/in/vehicle_mocap_odometry
/px4_3/fmu/in/vehicle_rates_setpoint
/px4_3/fmu/in/vehicle_trajectory_bezier
/px4_3/fmu/in/vehicle_trajectory_waypoint
/px4_3/fmu/in/vehicle_visual_odometry
/px4_3/fmu/out/failsafe_flags
/px4_3/fmu/out/sensor_combined
/px4_3/fmu/out/timesync_status
/px4_3/fmu/out/vehicle_attitude
/px4_3/fmu/out/vehicle_control_mode
/px4_3/fmu/out/vehicle_global_position
/px4_3/fmu/out/vehicle_gps_position
/px4_3/fmu/out/vehicle_local_position
/px4_3/fmu/out/vehicle_odometry
/px4_3/fmu/out/vehicle_status
/rosout

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