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Controlling Multiple Ardupilot Drones Via MAVROS

In this tutorial you will learn how to use the iq_gnc functions to control multiple drones on the same ros network.

Launching a MAVROS Instance for Each Drone

Each ardupilot SITL instance creates a couple of unique MAVlink streams. This is shown in your mavproxy terminal when you launch your ardupilot instance. For example when launching ardupilot with the below launch options

sim_vehicle.py -v ArduCopter -f gazebo-drone2 -I1

the output mavlink streams are show as follows

SIM_VEHICLE: "mavproxy.py" "--master" "tcp:127.0.0.1:5770" "--sitl" "127.0.0.1:5511" "--out" "127.0.0.1:14560" "--out" "127.0.0.1:14561"

We will need to tell MAVROS which udp interface to use for the drone we want MAVROS to connect to. For this vehicle the interface we will be using is 14561. To tell MAVROS to use this port we will launch with the following

roslaunch iq_sim apm.launch fcu_url:=udp://127.0.0.1:14561@14565 mavros_ns:=/drone2 tgt_system:=2

You will notice in the command above the argument mavros_ns:=/drone2. This is to create a unique mavros topic for each vehicle. For example

/mavros/global_position/local

will become

/drone1/mavros/global_position/local

you will also notice the launch argument tgt_system:=2 is passed. This corresponds to the SYSID_THISMAV parameter we set in the gazebo-droneX.parm files in the previous tutorial.

Executing a Multi-Drone Swarm Mission

note if you have not updated your iq_sim and iq_gnc repos lately, go ahead and run a git pull in both iq_sim and iq_gnc

In this example we will use our previously created square.cpp program in conjunction with the multi_drone.world gazebo sim.

first make a copy of square.cpp and call it multi_square.cpp.

We will be creating a drone swarm where each drone flies a synchronized square pattern. Instead of having to change each drone to GUIDED manually, we will be having the program initiate on start. To do this we will be replacing wait4start(); with set_mode("GUIDED");. This is the only code change that will be needed.

Next we are going to setup a new launch file to launch each drone's gnc code. Create a new file in launch called multi_square.launch

<launch>
	<group>
		<node pkg="iq_gnc" type="square" name="square1" output="screen" ns="/drone1">
			<param name="namespace" value="/drone1"/>
			<param name="use_sim_time"  value="true" />
		</node>
	</group>

	<group>
		
		<node pkg="iq_gnc" type="square" name="square2" output="screen" ns="/drone2">
			<param name="namespace" value="/drone2"/>
			<param name="use_sim_time"  value="true" />
		</node>
	</group>
	<group>	
		<node pkg="iq_gnc" type="square" name="square3" output="screen" ns="/drone3">
			<param name="namespace" value="/drone3"/>
			<param name="use_sim_time"  value="true" />
		</node>
	</group>
</launch>

you will notice the below line

<param name="namespace" value="/drone4"/>

this parameter tells the gnc_functions what namespace this program's mavros topics fall under.

The next thing we will need to do is setup a mavros launch file to create the needed links between the drone and the companion computer ros environment.

create the file multi-am.launch within iq_sim/launch

add the below

<launch>
	<node pkg="mavros" type="mavros_node" name="mavros" required="false" clear_params="true" output="screen" respawn="true" ns="/drone1">
		<param name="fcu_url" value="udp://127.0.0.1:14551@14555" />
		<param name="gcs_url" value="" />
		<param name="target_system_id" value="1" />
		<param name="target_component_id" value="1" />
		<param name="fcu_protocol" value="v2.0" />

		<!-- load blacklist, config -->
		<rosparam command="load" file="$(find mavros)/launch/apm_pluginlists.yaml" />
		<rosparam command="load" file="$(find mavros)/launch/apm_config.yaml" />
	</node>

	<node pkg="mavros" type="mavros_node" name="mavros" required="false" clear_params="true" output="screen" respawn="true" ns="/drone2">
		<param name="fcu_url" value="udp://127.0.0.1:14561@14565" />
		<param name="gcs_url" value="" />
		<param name="target_system_id" value="2" />
		<param name="target_component_id" value="1" />
		<param name="fcu_protocol" value="v2.0" />

		<!-- load blacklist, config -->
		<rosparam command="load" file="$(find mavros)/launch/apm_pluginlists.yaml" />
		<rosparam command="load" file="$(find mavros)/launch/apm_config.yaml" />
	</node>
	<node pkg="mavros" type="mavros_node" name="mavros" required="false" clear_params="true" output="screen" respawn="true" ns="/drone3">
		<param name="fcu_url" value="udp://127.0.0.1:14571@14575" />
		<param name="gcs_url" value="" />
		<param name="target_system_id" value="3" />
		<param name="target_component_id" value="1" />
		<param name="fcu_protocol" value="v2.0" />

		<!-- load blacklist, config -->
		<rosparam command="load" file="$(find mavros)/launch/apm_pluginlists.yaml" />
		<rosparam command="load" file="$(find mavros)/launch/apm_config.yaml" />
	</node>
</launch>
  • you will notice that the fcu_url increments by 10 for each corresponding udp port for the drones.
  • the target_system_id increments by 1 for each instance.
  • you will notice that each node has a unique ns (namespace). this will put a unique topic prefix for each mavros topic

You will notice that launching each ardupilot instance might be tedious, so it might be helpful to create the below shell script as multi-ardupilot.sh

#!/bin/bash

gnome-terminal \
 --tab -e "sim_vehicle.py -v ArduCopter -f gazebo-drone1 -I0" \
 --tab -e "sim_vehicle.py -v ArduCopter -f gazebo-drone2 -I1" \
 --tab -e "sim_vehicle.py -v ArduCopter -f gazebo-drone3 -I2" \

Running the Program

Run the gazebo sim

roslaunch iq_sim multi_drone.launch

Run the ardupilot instances

./multi-ardupilot.sh

Run the mavros instances

roslaunch iq_sim multi-apm.launch

Run the guidance program

roslaunch iq_gnc multi_square.launch