H2C FTS works fine on each input separately, but fails when using both

Bambu Lab H2 Series
1

I have an H2C with 3 AMS 2 Pro units, 2 AMS HT units, two 4-in-1 adapters, and an FTS

Multicolor prints are unreliable. Eventually, I get “AMS feed resistance is too high,” clicking from an AMS, failed loading or retraction, or filament that reaches the toolhead but will not load into the extruder

Sometimes Resume works, but another failure usually appears later, so I have to constantly babysit the printer

Both FTS inputs work fine when tested separately

The same test print completed through each input, and two AMS units also worked together through one 4-in-1 and one FTS input

The failures return when the same print alternates between both FTS inputs

I have tried different AMS units, slots and filaments, short PTFE paths, removing the 4-in-1 cleaning pad, loosening the FTS housing screws, the latest Studio beta, rebuilding my older FTS, and the AMS hub spring fix

This is already my second FTS, and both had the same issue

The FTS firmware is 00.00.16.62

Has anyone fixed this exact problem? I am considering buying a third FTS, but I am worried it will behave exactly the same

2

You probably will need to show us your setup.

Have you printed and installed the PTFE guides that go on the back of your AMS units?

3

There are many possibilities of why you are having the issues you are, but the simple fact is… they didn’t do a good job on this accessory. I don’t think you can get a very reliable setup with this accessory. I find CF/GF infused filaments are the worse followed by wood infused filaments. So if you can, stay away from those.

But the single take away is… its not a good accessory. Its super useful, and well intentioned, but not very functional. IMO, they should go back to the drawing board and stop selling it for the H series at the minimum.

4

Yes, I have already installed PTFE guides behind the AMS units. I used the adjustable guides on the tubes, and on the lower AMS I also installed Bambu Lab’s original PTFE guide. Neither made any difference.

The important detail is that the system works when I use only one FTS input. I can even use multiple AMS units through the same splitter and the same FTS input without errors.

The feed-resistance warnings return when AMS units connected to both FTS inputs are used in the same print. Because the exact same AMS units and PTFE paths work when only one FTS input is active, this does not appear to be caused simply by the PTFE tube routing or bends behind the AMS units.