Multi-Vehicle Sim | PX4 User Guide

Last updated 1 year ago

This topic explains how to simulate multiple UAV vehicles using and SITL (Linux only). A different approach is used for simulation with and without ROS.

Multiple Vehicle with Gazebo Classic

To simulate multiple iris or plane vehicles in Gazebo Classic use the following commands in the terminal (from the root of the Firmware tree):

<model>: The to spawn, e.g.: iris (default), plane, standard_vtol, rover, r1_rover typhoon_h480.
<number_of_vehicles>: The number of vehicles to spawn. Default is 3. Maximum is 254.
<world>: The that the vehicle should be spawned into, e.g.: empty (default)
<script>: Spawn multiple vehicles of different types (overriding the values in -m and -n). For example:
- Supported vehicle types are: iris, plane, standard_vtol, rover, r1_rover typhoon_h480.
- The number after the colon indicates the number of vehicles (of that type) to spawn.
- Maximum number of vehicles is 254.
<target>: build target, e.g: px4_sitl_default (default), px4_sitl_nolockstep
<label> : specific label for model, e.g: rplidar

Each vehicle instance is allocated a unique MAVLink system id (2, 3, 4, etc.). MAVLink system id 1 is skipped in order to have consistency among . Vehicle instances are accessed from sequentially allocated PX4 remote UDP ports: 14541 - 14548 (additional instances are all accessed using the same remote UDP port: 14549).

:::note The 254-vehicle limitation occurs because mavlink MAV_SYS_ID only supports 255 vehicles in the same network (and the first one is skipped). The MAV_SYS_ID is allocated in the SITL rcS: :::

Video: Multiple Multicopter (Iris)

Video: Multiple Plane

Video: Multiple VTOL

Build and Test (XRCE-DDS)

Tools/simulation/gazebo-classic/sitl_multiple_run.sh can be used to simulate multiple vehicles connected via XRCE-DDS in Gazebo Classic.

To build an example setup, follow the steps below:

Clone the PX4/Firmware code, then build the SITL code:
Run Tools/simulation/gazebo-classic/sitl_multiple_run.sh. For example, to spawn 4 vehicles, run:
:::note Each vehicle instance is allocated a unique MAVLink system id (2, 3, 4, etc.). MAVLink system id 1 is skipped. :::
Run MicroXRCEAgent. It will automatically connect to all four vehicles:

Multiple Vehicles with MAVROS and Gazebo Classic

This example demonstrates a setup that opens the Gazebo Classic client GUI showing two Iris vehicles in an empty world. You can then control the vehicles with QGroundControl and MAVROS in a similar way to how you would manage a single vehicle.

Required

Build and Test

To build an example setup, follow the step below:

Clone the PX4/PX4-Autopilot code, then build the SITL code
Source your environment:
Run launch file:
:::note You can specify gui:=false in the above roslaunch to launch Gazebo Classic without its UI. :::

The tutorial example opens the Gazebo Classic client GUI showing two Iris vehicles in an empty world.

You can control the vehicles with QGroundControl or MAVROS in a similar way to how you would manage a single vehicle:

QGroundControl will have a drop-down to select the vehicle that is "in focus"
MAVROS requires that you include the proper namespace before the topic/service path (e.g. for <group ns="uav1"> you'll use /uav1/mavros/mission/push).

What's Happening?

For each simulated vehicle, the following is required:

:::note If you are using the same vehicle model, you don't need a separate xacro file for each vehicle. The same xacro file is adequate. :::

The launch file multi_uav_mavros_sitl.launchdoes the following,

loads a world in Gazebo Classic,
for each vehicle,
- creates urdf model from xacro, loads gazebo classic model and runs PX4 SITL app instance
- runs a mavros node
:::note The complete block for each vehicle is enclosed in a set of <group> tags to separate the ROS namespaces of the vehicles. :::

To add a third iris to this simulation there are two main components to consider:

add UAV3 to multi_uav_mavros_sitl.launch
- duplicate the group of either existing vehicle (UAV1 or UAV2)
- increment the ID arg to 3
- select a different port for mavlink_udp_port arg for communication with Gazebo Classic
- selects ports for MAVROS communication by modifying both port numbers in the fcu_url arg
create a startup file, and change the file as follows:
- make a copy of an existing iris rcS startup file (iris_1 or iris_2) and rename it iris_3
- MAV_SYS_ID value to 3
- SITL_UDP_PRT value to match that of the mavlink_udp_port launch file arg
- the first mavlink start port and the mavlink stream port values to the same values, which is to be used for QGC communication
- the second mavlink start ports need to match those used in the launch file fcu_url arg
  :::note Be aware of which port is src and dst for the different endpoints. :::

Multiple Vehicles using SDF Models

This section shows how developers can simulate multiple vehicles using vehicle models defined in Gazebo Classic SDF files (instead of using models defined in the ROS Xacro file, as discussed in the rest of this topic).

The steps are:

Install xmlstarlet from your Linux terminal:
Use roslaunch with the multi_uav_mavros_sitl_sdf.launch launch file:

This method is similar to using the xacro except that the SITL/Gazebo Classic port number is automatically inserted by xmstarlet for each spawned vehicle, and does not need to be specified in the SDF file.

To add a new vehicle, you need to make sure the model can be found (in order to spawn it in Gazebo Classic), and PX4 needs to have an appropriate corresponding startup script.

You can choose to do either of:
- modify the single_vehicle_spawn_sdf.launch file to point to the location of your model by changing the line below to point to your model:
  :::note Ensure you set the vehicle argument even if you hardcode the path to your model. :::
- copy your model into the folder indicated above (following the same path convention).

Additional Resources

Last updated 1 year ago