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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.

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

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

  1. # Import DroneKit-Python
  2. from dronekit import connect, Command, LocationGlobal
  3. from pymavlink import mavutil
  4. import time, sys, argparse, math

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

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

Display some basic status information

  1. # Display basic vehicle state
  2. print " Type: %s" % vehicle._vehicle_type
  3. print " Armed: %s" % vehicle.armed
  4. print " System status: %s" % vehicle.system_status.state
  5. print " GPS: %s" % vehicle.gps_0
  6. 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.

  1. ################################################################################################
  2. # @File DroneKitPX4.py
  3. # Example usage of DroneKit with PX4
  4. #
  5. # @author Sander Smeets <sander@droneslab.com>
  6. #
  7. # Code partly based on DroneKit (c) Copyright 2015-2016, 3D Robotics.
  8. ################################################################################################
  10. # Import DroneKit-Python
  11. from dronekit import connect, Command, LocationGlobal
  12. from pymavlink import mavutil
  13. import time, sys, argparse, math
  16. ################################################################################################
  17. # Settings
  18. ################################################################################################
  20. connection_string       = '127.0.0.1:14540'
  21. MAV_MODE_AUTO   = 4
  22. # https://github.com/PX4/PX4-Autopilot/blob/master/Tools/mavlink_px4.py
  25. # Parse connection argument
  26. parser = argparse.ArgumentParser()
  27. parser.add_argument("-c", "--connect", help="connection string")
  28. args = parser.parse_args()
  30. if args.connect:
  31.     connection_string = args.connect
  34. ################################################################################################
  35. # Init
  36. ################################################################################################
  38. # Connect to the Vehicle
  39. print "Connecting"
  40. vehicle = connect(connection_string, wait_ready=True)
  42. def PX4setMode(mavMode):
  43.     vehicle._master.mav.command_long_send(vehicle._master.target_system, vehicle._master.target_component,
  44.                                                mavutil.mavlink.MAV_CMD_DO_SET_MODE, 0,
  45.                                                mavMode,
  46.                                                0, 0, 0, 0, 0, 0)
  50. def get_location_offset_meters(original_location, dNorth, dEast, alt):
  51.     """
  52.     Returns a LocationGlobal object containing the latitude/longitude `dNorth` and `dEast` metres from the
  53.     specified `original_location`. The returned Location adds the entered `alt` value to the altitude of the `original_location`.
  54.     The function is useful when you want to move the vehicle around specifying locations relative to
  55.     the current vehicle position.
  56.     The algorithm is relatively accurate over small distances (10m within 1km) except close to the poles.
  57.     For more information see:
  58.     http://gis.stackexchange.com/questions/2951/algorithm-for-offsetting-a-latitude-longitude-by-some-amount-of-meters
  59.     """
  60.     earth_radius=6378137.0 #Radius of "spherical" earth
  61.     #Coordinate offsets in radians
  62.     dLat = dNorth/earth_radius
  63.     dLon = dEast/(earth_radius*math.cos(math.pi*original_location.lat/180))
  65.     #New position in decimal degrees
  66.     newlat = original_location.lat + (dLat * 180/math.pi)
  67.     newlon = original_location.lon + (dLon * 180/math.pi)
  68.     return LocationGlobal(newlat, newlon,original_location.alt+alt)
  74. ################################################################################################
  75. # Listeners
  76. ################################################################################################
  78. home_position_set = False
  80. #Create a message listener for home position fix
  81. @vehicle.on_message('HOME_POSITION')
  82. def listener(self, name, home_position):
  83.     global home_position_set
  84.     home_position_set = True
  88. ################################################################################################
  89. # Start mission example
  90. ################################################################################################
  92. # wait for a home position lock
  93. while not home_position_set:
  94.     print "Waiting for home position..."
  95.     time.sleep(1)
  97. # Display basic vehicle state
  98. print " Type: %s" % vehicle._vehicle_type
  99. print " Armed: %s" % vehicle.armed
  100. print " System status: %s" % vehicle.system_status.state
  101. print " GPS: %s" % vehicle.gps_0
  102. print " Alt: %s" % vehicle.location.global_relative_frame.alt
  104. # Change to AUTO mode
  105. PX4setMode(MAV_MODE_AUTO)
  106. time.sleep(1)
  108. # Load commands
  109. cmds = vehicle.commands
  110. cmds.clear()
  112. home = vehicle.location.global_relative_frame
  114. # takeoff to 10 meters
  115. wp = get_location_offset_meters(home, 0, 0, 10);
  116. 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)
  117. cmds.add(cmd)
  119. # move 10 meters north
  120. wp = get_location_offset_meters(wp, 10, 0, 0);
  121. 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)
  122. cmds.add(cmd)
  124. # move 10 meters east
  125. wp = get_location_offset_meters(wp, 0, 10, 0);
  126. 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)
  127. cmds.add(cmd)
  129. # move 10 meters south
  130. wp = get_location_offset_meters(wp, -10, 0, 0);
  131. 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)
  132. cmds.add(cmd)
  134. # move 10 meters west
  135. wp = get_location_offset_meters(wp, 0, -10, 0);
  136. 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)
  137. cmds.add(cmd)
  139. # land
  140. wp = get_location_offset_meters(home, 0, 0, 10);
  141. 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)
  142. cmds.add(cmd)
  144. # Upload mission
  145. cmds.upload()
  146. time.sleep(2)
  148. # Arm vehicle
  149. vehicle.armed = True
  151. # monitor mission execution
  152. nextwaypoint = vehicle.commands.next
  153. while nextwaypoint < len(vehicle.commands):
  154.     if vehicle.commands.next > nextwaypoint:
  155.         display_seq = vehicle.commands.next+1
  156.         print "Moving to waypoint %s" % display_seq
  157.         nextwaypoint = vehicle.commands.next
  158.     time.sleep(1)
  160. # wait for the vehicle to land
  161. while vehicle.commands.next > 0:
  162.     time.sleep(1)
  165. # Disarm vehicle
  166. vehicle.armed = False
  167. time.sleep(1)
  169. # Close vehicle object before exiting script
  170. vehicle.close()
  171. time.sleep(1)