External telemetry link not working in Gazebo HITL

I’m running a HITL simulation with the Pixhawk 4 and Gazebo. It works fine and I can see the telemetry data on QGroundControl over UDP on the computer connected to the pixhawk over USB running gazebo. To make the simulation as close to reality as possible I would like to see the flight data on a separate computer over a Holybro telemetry link connected on TELEM 1. QGC on the second computer shows a vehicle connected but the link just times out and no actions can be performed. Could this be a hardware problem with the serial connections? When not in HITL mode the link works fine

It sounds like information is flowing from Pixhawk to QGC but not the other direction. Given the link works when not in HITL this means something is wrong in software.

I’d have to try to reproduce this to debug it. I’m putting it on the list.

In the meantime you could try to forward the UDP packets that Gazebo forwards using mavlink-router. MAVLink traffic is forward to 14550 for QGC as well as 14540 for MAVSDK or MAVROS. Therefore, you could route the UDP messages from 14540 to 14550 on the other machine.

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I just tried to reproduce this with latest master and it works fine for me.

Make sure to disable QGC to auto-connect on UDP so that it only uses the SiK radio.