Using DroneKit to communicate with PX4

DroneKit helps you create powerful apps for UAVs. These apps run on a UAV’s Companion Computer, and augment the autopilot by performing tasks that are both computationally intensive and require a low-latency link (e.g. computer vision).

DroneKit and PX4 are currently working on getting full compatibility. As of DroneKit-python 2.2.0 there is basic support for mission handling and vehicle monitoring.

Setting up DroneKit with PX4

Start by installing DroneKit-python from the current master.

git clone https://github.com/dronekit/dronekit-python.git
cd ./dronekit-python
sudo python setup.py build
sudo python setup.py install

Create a new python file and import DroneKit, pymavlink and basic modules

# Import DroneKit-Python
from dronekit import connect, Command, LocationGlobal
from pymavlink import mavutil
import time, sys, argparse, math

Connect to a MAVLink port of your drone or simulation (e.g. JMavSim).

# Connect to the Vehicle
print "Connecting"
connection_string = '127.0.0.1:14540'
vehicle = connect(connection_string, wait_ready=True)

Display some basic status information

# Display basic vehicle state
print " Type: %s" % vehicle._vehicle_type
print " Armed: %s" % vehicle.armed
print " System status: %s" % vehicle.system_status.state
print " GPS: %s" % vehicle.gps_0
print " Alt: %s" % vehicle.location.global_relative_frame.alt

Full mission example

The following python script shows a full mission example using DroneKit and PX4. Mode switching is not yet fully supported from DroneKit, we therefor send our own custom mode switching commands.

################################################################################################
# @File DroneKitPX4.py
# Example usage of DroneKit with PX4
#
# @author Sander Smeets <[email protected]>
#
# Code partly based on DroneKit (c) Copyright 2015-2016, 3D Robotics.
################################################################################################

# Import DroneKit-Python
from dronekit import connect, Command, LocationGlobal
from pymavlink import mavutil
import time, sys, argparse, math


################################################################################################
# Settings
################################################################################################

connection_string       = '127.0.0.1:14540'
MAV_MODE_AUTO   = 4
# https://github.com/PX4/Firmware/blob/master/Tools/mavlink_px4.py


# Parse connection argument
parser = argparse.ArgumentParser()
parser.add_argument("-c", "--connect", help="connection string")
args = parser.parse_args()

if args.connect:
    connection_string = args.connect


################################################################################################
# Init
################################################################################################

# Connect to the Vehicle
print "Connecting"
vehicle = connect(connection_string, wait_ready=True)

def PX4setMode(mavMode):
    vehicle._master.mav.command_long_send(vehicle._master.target_system, vehicle._master.target_component,
                                               mavutil.mavlink.MAV_CMD_DO_SET_MODE, 0,
                                               mavMode,
                                               0, 0, 0, 0, 0, 0)



def get_location_offset_meters(original_location, dNorth, dEast, alt):
    """
    Returns a LocationGlobal object containing the latitude/longitude `dNorth` and `dEast` metres from the
    specified `original_location`. The returned Location adds the entered `alt` value to the altitude of the `original_location`.
    The function is useful when you want to move the vehicle around specifying locations relative to
    the current vehicle position.
    The algorithm is relatively accurate over small distances (10m within 1km) except close to the poles.
    For more information see:
    http://gis.stackexchange.com/questions/2951/algorithm-for-offsetting-a-latitude-longitude-by-some-amount-of-meters
    """
    earth_radius=6378137.0 #Radius of "spherical" earth
    #Coordinate offsets in radians
    dLat = dNorth/earth_radius
    dLon = dEast/(earth_radius*math.cos(math.pi*original_location.lat/180))

    #New position in decimal degrees
    newlat = original_location.lat + (dLat * 180/math.pi)
    newlon = original_location.lon + (dLon * 180/math.pi)
    return LocationGlobal(newlat, newlon,original_location.alt+alt)





################################################################################################
# Listeners
################################################################################################

home_position_set = False

#Create a message listener for home position fix
@vehicle.on_message('HOME_POSITION')
def listener(self, name, home_position):
    global home_position_set
    home_position_set = True



################################################################################################
# Start mission example
################################################################################################

# wait for a home position lock
while not home_position_set:
    print "Waiting for home position..."
    time.sleep(1)

# Display basic vehicle state
print " Type: %s" % vehicle._vehicle_type
print " Armed: %s" % vehicle.armed
print " System status: %s" % vehicle.system_status.state
print " GPS: %s" % vehicle.gps_0
print " Alt: %s" % vehicle.location.global_relative_frame.alt

# Change to AUTO mode
PX4setMode(MAV_MODE_AUTO)
time.sleep(1)

# Load commands
cmds = vehicle.commands
cmds.clear()

home = vehicle.location.global_relative_frame

# takeoff to 10 meters
wp = get_location_offset_meters(home, 0, 0, 10);
cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_TAKEOFF, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
cmds.add(cmd)

# move 10 meters north
wp = get_location_offset_meters(wp, 10, 0, 0);
cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
cmds.add(cmd)

# move 10 meters east
wp = get_location_offset_meters(wp, 0, 10, 0);
cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
cmds.add(cmd)

# move 10 meters south
wp = get_location_offset_meters(wp, -10, 0, 0);
cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
cmds.add(cmd)

# move 10 meters west
wp = get_location_offset_meters(wp, 0, -10, 0);
cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_WAYPOINT, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
cmds.add(cmd)

# land
wp = get_location_offset_meters(home, 0, 0, 10);
cmd = Command(0,0,0, mavutil.mavlink.MAV_FRAME_GLOBAL_RELATIVE_ALT, mavutil.mavlink.MAV_CMD_NAV_LAND, 0, 1, 0, 0, 0, 0, wp.lat, wp.lon, wp.alt)
cmds.add(cmd)

# Upload mission
cmds.upload()
time.sleep(2)

# Arm vehicle
vehicle.armed = True

# monitor mission execution
nextwaypoint = vehicle.commands.next
while nextwaypoint < len(vehicle.commands):
    if vehicle.commands.next > nextwaypoint:
        display_seq = vehicle.commands.next+1
        print "Moving to waypoint %s" % display_seq
        nextwaypoint = vehicle.commands.next
    time.sleep(1)

# wait for the vehicle to land
while vehicle.commands.next > 0:
    time.sleep(1)


# Disarm vehicle
vehicle.armed = False
time.sleep(1)

# Close vehicle object before exiting script
vehicle.close()
time.sleep(1)