Hi Tamas, this video is how to get the voxl2 running with HITL: https://www.youtube.com/watch?v=ysvpJdXFWaM&ab_channel=AscendEngineering
Also - unless you are running the voxl-dev branch, then you will not be able to do a SERIAL connection from the voxl2 to QGC, you can only leverage a UDP connection. If you are running the voxl-dev branch and flashed the board, then you can leverage the voxl-px4-hitl
executable and connect to QGC. However, you cannot have gazebo open simultaneously because the serial connection will then be interrupted.
If you wish to run HITL while running QGC, then run this using an FTDI cable and then turn on the required services (voxl-vision-px4, voxl-mavlink-server) and then connect to gazebo serially, and QGC via UDP signal.
Let me know if this makes sense.