Need a serial comms protocol for rs485

I have worked out that I need to have several computers on plane:-
 1. Ground comms
 2. Flight control and waypoint intergrater
 3. APM interface
 4. Image processing

My idea is to run to serial bus links both in a multi-master arrangement. The link will need to have a watchdog running, and if a path cannot be made it will switch to the second link.

I will need to send mavlink and files across the link. I understand that I could possibly extend mavlink to also send files and images, but will it handle the flight control and a fairly continuous stream of images and 3d mesh.

The bus will also need to have some addressing and work on non-guaranteed communication. Whilst not expecting any connection issues, it must be catered for and as the data has a short time to live, protocols like TCP are not appropriate.
 

Setting up an APM is not always easy....

It's been a while since my last post as I have been trying to get the APM to work.
It turns out that JP1 on the APM appears to not power the servo out as stated in the manual. But this is not a problem as I will be using a BEC in-line after the Power Module for the APM.

I have also decided to change the power over to Lipo batteries as I want to drop the weight in the plane.

Also got the remote to change between stabilized and auto flight.