Quick hack to override RC over MAVLink with arrow keys

override_rc.py

#!/usr/bin/env python

import sys, os
from optparse import OptionParser
import Tkinter as tk

# tell python where to find mavlink so we can import it
sys.path.append(os.path.join(os.path.dirname(os.path.realpath(__file__)), '../mavlink'))
from pymavlink import mavutil

class App(tk.Frame):
	def __init__(self, tkroot, mavmaster):
		tk.Frame.__init__(self, tkroot)
		self.mavmaster = mavmaster
		self.tkroot = tkroot
		self.validkeys = ['Right', 'Left', 'Up', 'Down']
		self.afterId = dict((k,None) for k in self.validkeys)
		self.keyState = dict((k,False) for k in self.validkeys)
		self.tkroot.bind_all('<Key>', self.keyPressed)
		self.tkroot.bind_all('<KeyRelease>', self.keyReleased)
	def keyPressed(self,event):
		if event.keysym == 'Escape':
			release_rc(self.mavmaster)
			self.quit()	
		if event.keysym in self.validkeys:
			if self.afterId[event.keysym] != None:
				self.after_cancel(self.afterId[event.keysym])
				self.afterId[event.keysym] = None
			else:
				self.keyState[event.keysym] = event.time
				processKeyCommand(self.mavmaster, self.keyState)
	def keyReleased(self,event):
		if event.keysym in self.validkeys:
			self.afterId[event.keysym] = self.after_idle(self.releaseKey, event)
	def releaseKey(self, event):
		self.afterId[event.keysym] = None
		self.keyState[event.keysym] = False
		processKeyCommand(self.mavmaster, self.keyState)

# release control back to the radio
def release_rc(master):
	# a value of 0 releases the control to what the radio says
	values = [ 0 ] * 8
	for i in xrange(1):
		master.mav.rc_channels_override_send(master.target_system, 
			master.target_component, *values)

# attempt to send a control.
# you can pass 0 to refer to what the radio says
# you can pass 0xFFFF to refer to keep the current value 
def send_rc(master, data):
	for i in xrange(1):
		master.mav.rc_channels_override_send(
			master.target_system, master.target_component, *data)
	print ("sending rc: %s"%data)

def processKeyCommand(master, keystate):
	amt = 100
	pitch = 1500
	roll = 1500
	# handle elevator stick
	if keystate['Up']:
		pitch -= amt	# nose down (to go forward)
	if keystate['Down']:
		pitch += amt	# nose up (to go back)
	if pitch == 1500:
		# if this stick is centered, just release it
		pitch = 0
	# handle aile stick
	if keystate['Left']:
		roll -= amt		# roll left
	if keystate['Right']:
		roll += amt		# roll right
	if roll == 1500:
		# if this stick is centered, just release it
		roll = 0
	# set data (0 means channel is released)
	data = [ 0 ] * 8
	data[0] = roll
	data[1] = pitch
	# send the data to the rc override command
	send_rc(master, data)


def main():

	# read command line options
	parser = OptionParser("readdata.py [options]")
	parser.add_option("--baudrate", dest="baudrate", type='int',
					  help="master port baud rate", default=115200)
	parser.add_option("--device", dest="device", default=None, help="serial device")
	parser.add_option("--rate", dest="rate", default=4, type='int', help="requested stream rate")
	parser.add_option("--source-system", dest='SOURCE_SYSTEM', type='int',
					  default=255, help='MAVLink source system for this GCS')
	parser.add_option("--showmessages", dest="showmessages", action='store_true',
					  help="show incoming messages", default=False)
	(opts, args) = parser.parse_args()
	
	if opts.device is None:
		print("You must specify a serial device")
		sys.exit(1)

	# create a mavlink serial instance
	master = mavutil.mavlink_connection(opts.device, baud=opts.baudrate)

	# wait for the heartbeat msg to find the system ID
	master.wait_heartbeat()

	# request data to be sent at the given rate
	master.mav.request_data_stream_send(master.target_system, master.target_component, 
		mavutil.mavlink.MAV_DATA_STREAM_ALL, opts.rate, 1)

	# start up the window to read arrow keys
	tkroot = tk.Tk()
	application = App(tkroot, master)
	tkroot.mainloop()


if __name__ == '__main__':
	main()

Hi Christopher,

I'm very interested in this project, looks very nice. I'm trying to do something similar at the minute.

I am using OpenCV to track a ground target and am interested in how to use the "mav.rc_channels_override" command but I am fairly new to MAVLink and Python.

Any chance you could give an example of how you would use the code you have written here (i.e what arguments need to be passed and an example of how to do this)?

Many Thanks,
Conor

Awesome example, Christopher! You saved me (and probably many others) a huge amount of time figuring out how to do this.

Awesome! Thanks alot, I was looking for something like this. Exactly what I need, now I can have this as a reference for my own application. :-)