@fma It was actually my initial thought when i was thinking of making a MMU2. Connect and run everything externally. However it does increase the complexity, was hoping to be able accomplish it only using the duet.

@dc42 the most critical actions for mmu is during unload/load of a filament where it could slip or jam. The way MMU2 handles it is to use a filament sensor to detect potential problems during load/unload.

Example when loading, move filament forward and check status of filament sensor. If doing this for X step and the filament sensor doesn't detect the filament you would do a retry phase, e.g back filament some and retry and if still doesn't succeed pause print for manual intervention.
Same principal would be used for unloading to verify it succeeds.

Unfortunately I don't see a way to solve this with Duet with its current functionality, and I don't have any suggestion on how it could be solved using GCode. Wish there were some sort of advanced scripting support.

I've made an MMU2 unit from some scrap parts I had laying around just as a Proof of Concept to see how if i could get it to work with Duet.

I haven't implemented any tramming which i do believe is important to avoid jams especially stringing is a problem.
I also think for it to be sort of reliable it needs to use some sort of filament sensor to check if the switch is successful or not so the print may be saved through manual intervention, though I haven't really found a way to solve this with Duet. I really would like to have some sort of conditional checking.