connecting via TCP

[Ricky-Millar]

hey, I think i've got a fundamental misunderstanding in how to connect to my drone, I'm trying to connect to mavlink through my tango2 tx's wifi.

I can get mission planner to connect using TCP, 192.168.4.1 port: 5760, But within MAVSDK
drone.connect(system_address="tcp://[192.168.4.1][:5760]")
Doesn't seem to connect. I assumed these would be the same as the address you would use for mission planner.

I have code working within jmavsim all fine, just struggling to transfer it over to the real world.

[julianoes]

The TCP connection is mostly untested because PX4 does not generally use TCP. What sort of radio are you using that gives you TCP?

Can you get the output of mavsdk_server, e.g. by using:

logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)

Or by starting mavsdk_server separately like this:

drone = System()
await drone.connect()

and then starting the mavsdk_server separately in another terminal. It is usually located in:

~/.local/lib/python3.9/site-packages/mavsdk/bin/mavsdk_server

(replace with your Python version)

[Ricky-Millar]

ah alright, ill have a play around with that, thanks. 

It's the TBS tango 2. their TCP seems to work substantially better than UDP (i get like 95% lost packets with UDP, I've heard it's some problem with the radio), but I'm honestly not sure why its that way, it's just what they recommend using at the moment.

[Ricky-Millar]

alright, the first method returns "None"

for the second method, I'm not sure how you start the server from their terminal, sorry I'm not the most experienced programmer!

The TCP connection is mostly untested because PX4 does not generally use TCP. What sort of radio are you using that gives you TCP?

Can you get the output of mavsdk_server, e.g. by using:

logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)

Or by starting mavsdk_server separately like this:

drone = System()
await drone.connect()

and then starting the mavsdk_server separately in another terminal. It is usually located in:

~/.local/lib/python3.9/site-packages/mavsdk/bin/mavsdk_server

(replace with your Python version)

[julianoes]

For the second method, remove the arguments in connect() like above.

And then open a separate console and run mavsdk_server like this:

~/.local/lib/python3.9/site-packages/mavsdk/bin/mavsdk_server tcp://192.168.4.1:5760

To find where your mavsdk_server binary is, you can also look for it, using:

find ~ -name mavsdk_server

[Ricky-Millar]

no matter if I try to connect first or not, assuming I've typed the right stuff into the console... I'm getting this error. Im on windows by the way

E1220 19:22:27.340000000  7244 server_chttp2.cc:50] {"created":"@1639981347.340000000","description":"No address added out of total 1 resolved","file":"D:\a\MAVSDK\MAVSDK\build\release\third_party\grpc\grpc\src\grpc\src\core\ext\transport\chttp2\server\chttp2_server.cc","file_line":587,"referenced_errors":[{"created":"@1639981347.340000000","description":"Failed to add port to server","file":"D:\a\MAVSDK\MAVSDK\build\release\third_party\grpc\grpc\src\grpc\src\core\lib\iomgr\tcp_server_windows.cc","file_line":512,"referenced_errors":[{"created":"@1639981347.340000000","description":"OS Error","file":"D:\a\MAVSDK\MAVSDK\build\release\third_party\grpc\grpc\src\grpc\src\core\lib\iomgr\tcp_server_windows.cc","file_line":208,"os_error":"Only one usage of each socket address (protocol/network address/port) is normally permitted.\r\n","syscall":"bind","wsa_error":10048}]}]}
Segmentation fault

[julianoes]

Aha you're on Windows. That's good to know. It looks like it fails to bind. Do you have Mission Planner running when you try this?

And btw. I assume you're using ArduPilot and not PX4? Note that support for ArduPilot in MAVSDK is only experimental, you can see more details in mavlink/MAVSDK#1568.

[Ricky-Millar]

Ah yes, I should have said all my hardware at the start. I didn't think it could have an effect as I thought the incoming stream of mavlink data would be the same.

So I'm trying out a fairly different set up. It's a betaflight fc, that is transmitting mavlink over crossfire to my tx, and then tcp from my tx to my laptop/phone

I'm trying to make a gps-based antenna tracker that works with betaflight. As I said I have got it working with mission planner, so the mavlink is making it through to my PC/phone, and the rest of my code works in jmavsim too. My end game was to try and implement this onto a microcontroller or a raspi or something later on once I've got my brain around getting it working on the PC.

[julianoes]

Ok cool!

Have you tried connecting without Mission Planner open? I think the problem is that Mission Planner is using the port which means MAVSDK cannot bind to it.

[JonasVautherin]

I don't think it's a binding error on the 192.168.4.1:5760 side, because here MAVSDK is a TCP client. It's not binding to anything, it's just opening a connection to a remote server (the drone that listens on 5760). Or did I miss something?

Just to be sure:

drone.connect(system_address="tcp://[192.168.4.1][:5760]")

This is invalid, right? The way to write that is:

drone.connect(system_address="tcp://192.168.4.1:5760")

Can you show us the command line you type and the corresponding output of ~/.local/lib/python3.9/site-packages/mavsdk/bin/mavsdk_server tcp://192.168.4.1:5760?

Because you are on Windows, I assume you did not copy-paste exactly that, so it would be interesting for us to see exactly what you wrote.

Still guessing, but the error message sounds like grpc gets an error saying "Failed to add port to server" and "Only one usage of each socket address (protocol/network address/port) is normally permitted". But to me this is happening when mavsdk_server creates the grpc server, not when it tries to connect to the remote drone. So not related to tcp://192.168.4.1:5760 but rather to mavsdk_server binding to 50051. Could you try a few different ports? With @julianoes' line above, it would be something like:

~/.local/lib/python3.9/site-packages/mavsdk/bin/mavsdk_server -p 55555 tcp://192.168.4.1:5760

Where -p 55555 tells mavsdk_server to listen on 55555 instead of 50051. Maybe 50051 is already used on your computer for some reason.

[Ricky-Millar]

Oh sorry, I totally forgot to reply to that bit.
I intentionally disconnected from mission planner before trying to connect

I'll just go and make sure it isn't running in the back ground or anything and try again..

[Ricky-Millar]

ok so, im on windows, to get that previous error I typed
'D:/Users/ricky/OneDrive/Desktop/100\ days\ of\ python/dronegpsmavlink/venv/Lib/site-packages/mavsdk/bin/mavsdk_server tcp://192.168.4.1:5760'
into a bash terminal.

as for the [192.168.4.1][:5760] vs 192.168.4.1:5760 i have tried them both, but I can type anything in there at the moment with the same results.

I just tried again double checking mission planner is not running and still, the same result.

BUT
port 55555 I think has worked! I get

$ D:/Users/ricky/OneDrive/Desktop/100\ days\ of\ python/dronegpsmavlink/venv/Lib/site-packages/mavsdk/bin/mavsdk_server -p 55555 tcp://192.168.4.1:5760
[08:44:49|Info ] MAVSDK version: v0.41.0 (D:\a\MAVSDK\MAVSDK\src\core\mavsdk_impl.cpp:21)
[08:44:49|Info ] Server started (D:\a\MAVSDK\MAVSDK\src\mavsdk_server\src\grpc_server.cpp:48)
[08:44:49|Info ] Server set to listen on 0.0.0.0:55555 (D:\a\MAVSDK\MAVSDK\src\mavsdk_server\src\grpc_server.cpp:49)
[08:44:49|Info ] Waiting to discover system on tcp://192.168.4.1:5760... (D:\a\MAVSDK\MAVSDK\src\mavsdk_server\src\connection_initiator.h:21)

You guys are pretty clever ay, haha. Any hints on how I could implement this into code?

[julianoes]

Ah, so the mavsdk_server port is already taken. Now the question is what is using 50051. You could try to reboot the computer to make sure whatever is using is, is shut down.

[Ricky-Millar]

got some more info for you, which I don't understand but maybe you do. I checked what is using the port 50051 in PowerShell to see what was blocking it, and it was another instance of mavsdk_server.
I killed mavsdk_server in task manager and the bash command started to work with the normal port. it works as long as I'm using
drone.connect()

But If I try to use drone.connect(system_address="tcp://192.168.4.1:5760") then is stopps working again. I can see mavsdk still using the port in powershell but its not in the task manager for me to kill anymore. I'm struggling to make this repeatable and am a bit out of my depth here.

on top of all that, when I do use a different port and get the server up and running, It is failing to connect. Ill keep trying different things for a bit. But I'm in NZ and its about bedtime so I might go quiet for a bit

[julianoes]

Good night over to NZ 👋

I killed mavsdk_server in task manager and the bash command started to work with the normal port. it works as long as I'm using
drone.connect()

So it connects and everything is working? And if not, please paste the output that it's printing so we can debug what is going on.

If you use drone.connect(system_address="tcp://192.168.4.1:5760") with the arguments, then it will start mavsdk_server in the background, so you can only do either or.