# Creating MAVLink commands from python

I am struggling to find any clear documentation on how to create MAVlink commands using python.

I am looking to create an autonomous glider and require some of the basic functions

• Retrieve GPS Data and store into a file
• Import GPS data in Python function
• Send waypoint lat, long, alt to the autopilot (APM)

I am currently using MAVProxy as my GCS and the ErleBrain 3 as my autopilot hardware but the aim is to not require a GCS and just have a python script to automatically add and remove waypoints based on the received GPS data

There are a couple libraries for doing what you want to to, the first is pyMAVlink and the second is dronekit-python it is going to be easiest to use dronekit as it handles a lot of the lower level stuff like processing incoming packets and connecting over your preferred interface for you automatically. I assume you want to load waypoints from a file and have your UAV fly them? In that case you probably want to set your UAV into Guided mode (for a description of modes on Ardupilot see the docs here) this will tell Ardupilot that you are going to command it step by step what to do.

Here is some example code form there wiki that does what you want to do you'll just have to load your files and transform the coordinates to lat lon points:

def arm_and_takeoff(aTargetAltitude):
while not vehicle.is_armable:
print " Waiting for vehicle to initialise..."
time.sleep(1)
vehicle.mode = VehicleMode("GUIDED")
vehicle.armed = True

while not vehicle.armed:
print " Waiting for arming..."
time.sleep(1)

print "Taking off!"
vehicle.simple_takeoff(aTargetAltitude)
# Wait for takeoff to finish
while True:
print " Altitude: ", vehicle.location.global_relative_frame.alt
if vehicle.location.global_relative_frame.alt>=aTargetAltitude*0.95: #Trigger just below target alt.
print "Reached target altitude"
break
time.sleep(1)

def get_distance_metres(aLocation1, aLocation2):
dlat = aLocation2.lat - aLocation1.lat
dlong = aLocation2.lon - aLocation1.lon
return math.sqrt((dlat*dlat) + (dlong*dlong)) * 1.113195e5

# define connection method
# see all the methods at http://python.dronekit.io/guide/connecting_vehicle.html
connection_string = "127.0.0.1:14550"

# Connect
# arm and takeooff to 10m
arm_and_takeoff(10)
# set airspeed to 3 m/s
vehicle.airspeed = 3

point1 = LocationGlobalRelative(-35.361354, 149.165218, 20)
vehicle.simple_goto(point1)

while vehicle.mode.name=="GUIDED": #Stop action if we are no longer in guided mode.
remainingDistance=get_distance_metres(vehicle.location.global_frame, point1)
print "Distance to target: ", remainingDistance
if remainingDistance<=targetDistance*0.01: #Just below target, in case of undershoot.
print "Reached target"
break;
time.sleep(2)


Per request I have some example pymavlink code, you can see some more examples here, sending messages is a pain, you need to identify what type of packet you need to send, and fill it's paramaters acording to the standard

from pymavlink import mavutil

notimestamps=True,
robust_parsing=True)

while True:
msg = data.recv_match();
#If we have a valid message
if msg is not None:
#print msg.get_type()
if msg.get_type() is "HEARTBEAT":
print msg.autopilot
elif msg.get_type() is "NAV_CONTROLLER_OUTPUT":
print msg

• Hi Mark, Thanks for your reply. Unfortunately I have to use pymavlink. Is there any example code to help me have some sense of direction. – car12398 Mar 2 '17 at 15:05
• Why do you have to use pymavlink? I can post some examples in a minute but you will have to extract the data in real time that you need, knowing what packets it's in, ect... I would strongly recommend DroneKit if you can use it. – Mark Omo Mar 2 '17 at 15:07
• I am using an Erle-brain and that apparently is not compatible with Dronekit according one of the developers. Do you know of any tutorial based websites that guide you through it? – car12398 Mar 2 '17 at 18:34
• that is false, Erle-brain runs ardupilot which uses mavlink and both Dronekit and pymavlink are both just mavlink interfaces, that can be used for any platform from the Navio2 to the Erle-brain to the Parrot bebop – Mark Omo Mar 2 '17 at 18:43
• Thank you for your help Mark, it would have been a lot easier if this was made clearer by Erle Brain! – car12398 Mar 9 '17 at 14:25