Trying to send some commands to pixhawk from pymavlink. What am I missing?

[Luk Jo]

Hi, i'm trying to set up some communication between linux computer and pixhawk via USB using pymavlink. To get started i just wanted to send some simple commands to pixhawk like MAV_CMD_COMPONENT_ARM_DISARM, or MAV_CMD_PREFLIGHT_REBOOT_SHUTDOWN  to see if it's working, but it doesn't. Please look at my python code:

#!/usr/bin/env python

'''
test mavlink messages
'''

import sys, struct, time, os
from curses import ascii

from pymavlink.dialects.v10 import common as mavlink

import mavtest
from pymavlink import mavutil


mav = mavlink.MAVLink_header(76,9,0,1,1)
command= mavlink.MAVLink_command_long_message(1,0,400,0,1,0,0,0,0,0,0) #arm pixhawk
msg = command.pack(mav) #prepare message to send


ser = mavutil.MavlinkSerialPort("/dev/ttyACM0", 115200,0,0,3,1) #open up serial port in debug mode

ser.write(msg) #send command via serial port
   
print msg




And here is my terminal OUTPUT:

root@kali:~/mavlink/pymavlink/examples# python mavlinktest1.py
Connecting with MAVLink to /dev/ttyACM0 ...
HEARTBEAT OK

Locked serial device

�! L�?� �>
root@kali:~/mavlink/pymavlink/examples#

As you can see it is receiving heartbeat, that means we have some sort of communication. But sending my message to pixhawk doesn't have any effect. For example when I try to send ARM command from mavproxy i can hear buzzer beeps etc.
Thank you for any suggestions :)