How to Connect ROS to PX4 for Drone Control

To connect ROS to PX4, use the MAVROS package which acts as a bridge between ROS and PX4's MAVLink protocol. Start PX4 on your drone or simulator, then run roslaunch mavros px4.launch fcu_url:=udp://:14540@localhost:14557 to establish communication.

Syntax

The main command to connect ROS to PX4 is:

• roslaunch mavros px4.launch: Launches MAVROS node that bridges ROS and PX4.
• fcu_url:=udp://:14540@localhost:14557: Parameter specifying the connection URL to PX4's flight controller.
• gcs_url:=: Optional parameter for ground control station URL.

This command starts the communication node that translates MAVLink messages between PX4 and ROS topics.

bash

roslaunch mavros px4.launch fcu_url:=udp://:14540@localhost:14557

Example

This example shows how to start PX4 SITL (Software In The Loop) simulator and connect it to ROS using MAVROS.

First, start PX4 SITL:

cd ~/PX4-Autopilot
make px4_sitl_default gazebo

Then, in a new terminal, launch MAVROS to connect ROS to PX4:

bash

roslaunch mavros px4.launch fcu_url:=udp://:14540@localhost:14557

Output

started roslaunch server
... [INFO] [mavros]: FCU URL: udp://:14540@localhost:14557
... [INFO] [mavros]: Plugin 3dr_radio loaded
... [INFO] [mavros]: Connected to FCU: PX4 Autopilot

Common Pitfalls

• Wrong connection URL: Using incorrect fcu_url causes MAVROS to fail connecting to PX4.
• Firewall or network issues: UDP ports must be open and not blocked.
• PX4 not running: Ensure PX4 SITL or hardware is active before launching MAVROS.
• Version mismatch: Use compatible versions of PX4, ROS, and MAVROS.

Example of a wrong and right connection URL:

bash

# Wrong (missing port)
roslaunch mavros px4.launch fcu_url:=udp://localhost

# Right
roslaunch mavros px4.launch fcu_url:=udp://:14540@localhost:14557

Quick Reference

Command/Parameter	Description
roslaunch mavros px4.launch	Launch MAVROS node to connect ROS to PX4
fcu_url:=udp://:14540@localhost:14557	Flight controller connection URL for UDP communication
make px4_sitl_default gazebo	Start PX4 SITL simulator with Gazebo
rosrun mavros mavcmd long 176 1 0 0 0 0 0	Example MAVROS command to arm the drone

Key Takeaways

Use MAVROS as the bridge between ROS and PX4 for communication.

Start PX4 SITL or hardware before launching MAVROS with the correct connection URL.

Ensure UDP ports and network settings allow communication between ROS and PX4.

Check version compatibility between PX4, ROS, and MAVROS to avoid connection issues.

Use roslaunch mavros px4.launch fcu_url:=udp://:14540@localhost:14557 to connect ROS to PX4.