How to Use MAVROS for Drone Control: Basic Guide

To use mavros for drone control, first install and launch the mavros node to connect to your drone's autopilot. Then, publish commands to topics like /mavros/setpoint_position/local to control movement and subscribe to telemetry topics for feedback.

Syntax

The basic syntax to use mavros involves launching the mavros node with connection parameters and then publishing or subscribing to ROS topics for control and telemetry.

• roslaunch mavros px4.launch fcu_url:=udp://:14540@: Launches MAVROS connecting to the drone autopilot via UDP.
• /mavros/setpoint_position/local: Topic to publish position commands.
• /mavros/state: Topic to subscribe to drone state information.
• /mavros/cmd/arming: Service to arm or disarm the drone.
• /mavros/set_mode: Service to change flight modes.

bash

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

# Publish position commands to /mavros/setpoint_position/local
# Subscribe to /mavros/state for drone status
# Use /mavros/cmd/arming service to arm/disarm
# Use /mavros/set_mode service to change flight mode

Example

This example shows how to arm the drone, set it to OFFBOARD mode, and send a position command to move it to a point 2 meters above the starting position.

python

import rospy
from mavros_msgs.msg import State
from mavros_msgs.srv import CommandBool, SetMode
from geometry_msgs.msg import PoseStamped

current_state = None

def state_cb(msg):
    global current_state
    current_state = msg

rospy.init_node('offboard_control')
state_sub = rospy.Subscriber('mavros/state', State, state_cb)
local_pos_pub = rospy.Publisher('mavros/setpoint_position/local', PoseStamped, queue_size=10)

rospy.wait_for_service('mavros/cmd/arming')
rospy.wait_for_service('mavros/set_mode')
arm_service = rospy.ServiceProxy('mavros/cmd/arming', CommandBool)
mode_service = rospy.ServiceProxy('mavros/set_mode', SetMode)

pose = PoseStamped()
pose.pose.position.x = 0
pose.pose.position.y = 0
pose.pose.position.z = 2

rate = rospy.Rate(20)

# Wait for connection
while not rospy.is_shutdown() and (current_state is None or not current_state.connected):
    rate.sleep()

# Send a few setpoints before starting
for i in range(100):
    local_pos_pub.publish(pose)
    rate.sleep()

# Set mode to OFFBOARD
mode_service(base_mode=0, custom_mode='OFFBOARD')
# Arm the drone
arm_service(True)

while not rospy.is_shutdown():
    local_pos_pub.publish(pose)
    rate.sleep()

Output

No direct output; drone moves to position (0,0,2) meters and stays there in OFFBOARD mode.

Common Pitfalls

• Not sending setpoints before switching to OFFBOARD mode: The autopilot requires a stream of setpoints before allowing OFFBOARD mode.
• Forgetting to arm the drone: Commands won't take effect if the drone is not armed.
• Incorrect connection URL: Ensure the fcu_url matches your drone's communication method (UDP, serial, etc.).
• Ignoring state feedback: Always check /mavros/state to confirm connection and mode changes.

python

## Wrong way: Switching to OFFBOARD mode without sending setpoints
mode_service(base_mode=0, custom_mode='OFFBOARD')

## Right way: Send setpoints first
for i in range(100):
    local_pos_pub.publish(pose)
    rate.sleep()
mode_service(base_mode=0, custom_mode='OFFBOARD')

Quick Reference

Command	Description
roslaunch mavros px4.launch fcu_url:=udp://:14540@	Launch MAVROS and connect to drone autopilot
Publish to /mavros/setpoint_position/local	Send position commands to control drone movement
Subscribe to /mavros/state	Monitor drone connection and mode status
Call /mavros/cmd/arming service	Arm or disarm the drone
Call /mavros/set_mode service	Change the drone's flight mode (e.g., OFFBOARD, MANUAL)

Key Takeaways

Always launch MAVROS with the correct connection URL to your drone autopilot.

Send a stream of setpoints before switching to OFFBOARD mode to enable external control.

Use the arming service to arm the drone before sending movement commands.

Monitor the drone state topic to confirm connection and mode changes.

Test commands in a safe environment to avoid unexpected drone behavior.