Doubts in pymavlink

Blue Robotics Software ArduSub
1

Sir,

I am using ubuntu 16.04 OS in my topside computer. The topside computer has an IP address 192.168.2.1. I have installed python2 and mavproxy in this computer. It is connected using ethernet to a raspberry pi whose IP is 192.168.2.2. The raspberry pi has been connected to pixhwk and latest ardusub software has been installed in it. As given in pymavlink page in ardusub, I followed the same code to “Run pyMavlink on the surface computer”. I wrote the code in some text editor, saved it as ‘file.py’ and tried to execute this file in the python shell. I didn’t get any output. Actually when I run he file, actually the vehicle information should come below the line . I have also checked by writing each line of the code individually in the python shell. Still I didn’t get any information from the vehicle(pixhawk). Am I following the correct steps? My doubt is whether, is this the way to send or receive mavlink messages using python? Please reply.

2

Hi,

Are you running the script with QGroundControl open ?
The script provides a small explanation about this:

# Create the connection
#  If using a companion computer
#  the default connection is available
#  at ip 192.168.2.1 and the port 14550
# Note: The connection is done with 'udpin' and not 'udpout'.
#  You can check in http:192.168.2.2:2770/mavproxy that the communication made for 14550
#  uses a 'udpbcast' (client) and not 'udpin' (server).
#  If you want to use QGroundControl in parallel with your python script,
#  it's possible to add a new output port in http:192.168.2.2:2770/mavproxy as a new line.
#  E.g: --out udpbcast:192.168.2.255:yourport

Also, can you check if the communication between your surface computer and the ROV is working with QGroundControl ? If QGC is not working, you should fix your connection configuration/hardware before running the script.

1 Like
3

Sir,
The topside computer is connected to raspberry pi through an ethernet cable. I had installed python-pip, python-future and pymavlink in my topside computer, along with python 2.7.12. I followed the commands given in the ardusub page ‘https://www.ardusub.com/developers/pymavlink.html’. For eg, if I wanted to send RC values to my vehicle, the command given in the page is as given below.

Import mavutil

from pymavlink import mavutil

Create the connection

master = mavutil.mavlink_connection(‘udpin:0.0.0.0:14550’)

Wait a heartbeat before sending commands

master.wait_heartbeat()

Create a function to send RC values

More information about Joystick channels

here: Redirecting...

def set_rc_channel_pwm(id, pwm=1500):
“”" Set RC channel pwm value
Args:
id (TYPE): Channel ID
pwm (int, optional): Channel pwm value 1100-1900
“”"
if id < 1:
print(“Channel does not exist.”)
return

# We only have 8 channels
#http://mavlink.org/messages/common#RC_CHANNELS_OVERRIDE
if id < 9:
    rc_channel_values = [65535 for _ in range(8)]
    rc_channel_values[id - 1] = pwm
    master.mav.rc_channels_override_send(
        master.target_system,                # target_system
        master.target_component,             # target_component
        *rc_channel_values)                  # RC channel list, in microseconds.

Set some roll

set_rc_channel_pwm(2, 1600)

Set some yaw

set_rc_channel_pwm(4, 1600)

The camera pwm value is the servo speed

and not the servo position

Set camera tilt to 45º with full speed

set_rc_channel_pwm(8, 1900)

The main doubt lies within the code. Here we gave a certain PWM value to each channel which implies we are setting the PWM value for yaw, roll etc which are the RC channel inputs. Now suppose, if I want the whole ardusub vehicle to move up/down, If I give the input " Vehicle up/down", all the thrusters which makes the vehicle to move up/down, should receive the PWM(it may be thruster2, thruster 3, thruster5) and these thruster should spin. Is it possible in ardusub using pymavlink. if so, How do I need to change the code?
Looking forward for your reply,

Thanking you,
Regards,
Deepak

4

Hi,

This example, as the comments explain, points how to send RC pwm values to the vehicle.
If you want to send Throttle, you should check the rc-inputs link in the example and use the channel that deals with Throttle information (channel number 3).

5

Just to clarify again the PWM values correspond to a particular motion (like forward, lateral, yaw) and not for a particular thruster?