Hi everyone.
I hope it is good place to put that subject.
I’m trying to build calibration equipment for echosounder. How the calibration looks like: link

That is practically very big Hangprinter without extruder.
Each engine (winch) is steering wireless (two way) with LoRa communication. The setup what I have is remote control with display and PS2 pad.
All stepper engines are with battery, Arduino, driver (TCM2130) and communication board. On my software a can move only one engine on the same time because all engines are not coordinated. I think that using existing software will be easier for upgrade it in the future.
This is not commercial project only scientific. It doesn't have to be super accurate.
I thought that remote control will be “master” board with Marlin firmware, and it will be sending commands to each engine separately (or together). Other “slave” board will be controlling the engines and of course position, with every maybe 10sec will be sending back to the “master”.

My problem is that I have no idea where in the “master” program should I disconnect software from engines and put their communication function.
Do someone of You know where is the place inside the program where are, let say, commands: “Left engine move 200 steps, Right 300 and Front -20 steps”?

Maybe You have better idea how to do it. Maybe remote control should send only g-code. Sorry I'm stuck and I need someone smarter than me.
Maybe I'll put some information what I already done.
2 years ago I built first prototype. Before it we had 3 people and one operator. Through radio we was calling to each person like "Adam lower 50 cm and Jon pull up 1m" and we was working like that for 20years.
Next it was 3 motors from drill machine, the really long (50m each) extension cables and 3 handles from drill machine inside operation room. Problem was that putting that cables through ship lasted 3-4 hours.
So I built wireless version, I attached polulu encoders to existing engines, driver for 12v motors arduino with LoRa communication board. Problem is that You can ster only one engine at time, encoders are really sensitive and can stop working or
even worse sending wrong pulses what correction algorithm interpret as uncontrolled movement so sometime engines didn't stop.
Now we have 3 stepper motors with gears and winches, and I don't want to go it like before in Partizant way.

Regards