Sending custom messages

Hi to everyone!

I try to understand how to send a custom message from a companion computer to a base station for the last two weeks. Most schematically, the situation is as follows:

Companion computers (NavQ) ==1==> FMU (RDDRONE-FMUK66) ==2==> base station (PC-Laptop)

On the NavQ a python app is working.

1 => serial link
2 => telemetry link (433 MHz)

I made some progress (I am able to send a custom message from the FMU to the base station, and the connection between NavQ and the FMU is working), but I cannot understand the big picture of the main concepts. How can a custom message be relayed through the FMU? How to send the custom message from the Python app placed on the companion computer, and how it is forwarded to the base station? Please, can someone help me?

Thank you very much!!!

From the last post I made some progress, but right now I have another problem:

Based on the MAVLink Messaging tutorial ( I followed all the step, but when I compile the code I get the error:

error: ‘MavlinkOrbSubscription’ does not name a type in mavlin_messages.c.

Searching I found that the MavlinkOrbSubscription class is included in the mavlink_orb_subscription.h file. But, I do not have a such file in all the project. I installed the PX4 using:

$ git clone --recursive px4-firmware

Please, do you have a solution? Thank you very much!

Dobrea Dan.