QGC Integration of winch data

Blue Robotics Software QGroundControl
1

Hello,
Working on a ROV and would like to integrate the winch cable counter into the QGC display. Is that possible?

1 Like
2

Hi @RURAS,

QGC is open source, so it’s definitely possible, but because of how the MAVLink protocol and the QGC codebase are structured it can be somewhat complicated to add things to the interface, and doing so requires building your own custom version of QGC.

A couple of years ago I did a write up about adding a sensor to a MAVLink stream. Most likely the simplest approach is something similar to that, using NAMED_VALUE_FLOAT messages. I’ve just tested and it worked for me to make these modifications to the latest stable version of QGC (Stable_V4.2 branch), which could then receive MAVLink messages from a program sending the relevant message, like this Pymavlink script:

import time
from pymavlink import mavutil

def wait_conn(device):
    """ Sends a ping to develop UDP communication and waits for a response. """
    while not (msg := device.recv_match()):
        device.mav.ping_send(
            int((time.time() - BOOT_TIME) * 1e6), # Unix time since boot (microseconds)
            0, # Ping number
            0, # Request ping of all systems
            0  # Request ping of all components
        )
        time.sleep(0.5)


class Winch:
    def __init__(self):
        ... # TODO: implement connection details
        # this is the name QGC is searching for, and MUST be 9 characters or shorter
        self.message_name = b'WinchTrns'
    
    def get_value(self):
        """ Returns the next value from the winch. """
        # TODO: implement actual data fetching
        # pretend to be a slow sensor, with some random output values
        from random import randint
        time.sleep(0.5)
        return randint(-50, 50)


if __name__ == '__main__':
    BOOT_TIME = time.time()
    # establish connection to top-side computer
    direction = 'udpout'
    device_ip = 'localhost'
    port      = 14550
    print(f'connecting to {device_ip} via {direction} on {port=}.')
    qgc = mavutil.mavlink_connection(f'{direction}:{device_ip}:{port}', source_system=1)
    
    print('waiting for confirmation... ', end='')
    wait_conn(qgc)
    print('connection success!')
    
    # TODO: connect to winch
    winch = Winch()
    
    while 'reading data':
        qgc.mav.named_value_float_send(
            int((time.time() - BOOT_TIME) * 1e3),
            winch.message_name,
            winch.get_value()
        )

From there you can modify the telemetry display (hover over it then click the edit pencil at the top left corner), and add it:

Screen Shot 2022-08-19 at 12.01.30 pm
Screen Shot 2022-08-19 at 12.01.30 pm486Ă—542 33 KB

Screen Shot 2022-08-19 at 12.02.42 pm
Screen Shot 2022-08-19 at 12.02.42 pm1226Ă—154 31.5 KB

As something of a side note, it seems the `Stable_V4.2` branch has a couple of warnings when trying to build, which I ignored to enable the build to complete (click to see details, if relevant)

by adding

QMAKE_CXXFLAGS_WARN_ON+=-Wno-unused-but-set-variable QMAKE_CXXFLAGS_WARN_ON+=-Wno-deprecated-declarations

as additional build arguments:

Screen Shot 2022-08-19 at 12.11.02 pm
Screen Shot 2022-08-19 at 12.11.02 pm1952Ă—1434 343 KB

Ordinarily warnings shouldn’t be ignored, but given the code causing the warnings was from a supposedly stable version I decided to leave it alone, since it’s unlikely to cause issues.

1 Like
3

Eliot,

Awsome, thanks will look into this.

J

1 Like
4

Project been in a hybernate state…
-a follow up question: Based on this, is it possible to convert the “Winch turn” to “XXX meter cable paid out” or “XXX meter cable recovered”

5

Hi @RURAS,

Yes, but the complexity of doing so would depend on the accuracy you want. The winch drum circumference is straightforward to calculate from the diameter, but for the most accurate results you would likely want to consider the thickness and number of layers of the tether itself currently on the drum.

As a side-note, the “Very Generic Indicator” widget in Cockpit[1] already allows specifying a constant multiplier, so if you’re using a thin tether on a large drum and/or only need a rough estimate then you wouldn’t even need a custom build to do that, which would likely make it quite a bit more straightforward than the QGroundControl approach.

  1. Cockpit is an upcoming control station software that Blue Robotics is developing as a replacement for QGroundControl. It’s currently only in an alpha state (not officially released), but it’s already installable as a BlueOS Extension if you want to try it out. ↩︎

6

Eliot, thanks for the reply. We have a sheave wheel with an encoder. One revolution equals to 150cm. So we like to get the enocder signal (revolutions converted into lenght) displayed on the screen.
is this possible?

7

As I’ve described above, you’ll need to create a script/program that reads your winch sensor and sends MAVLink messages reporting its state, in which case displaying the length is possible

  • in Cockpit via the Very Generic Indicator widget
  • in QGC if you modify the code and create a custom build with support for your winch message
1 Like