Filament cutter at extruder, and motorised rewinder.
I gave up on my MMU2s a year or so ago, but based on looking at the design of the AMS on the Bambu labs printer - I like in particular the cutter at the extruder and the motorised rewinding.
1. Filament cutter at the extruder - could some sort of cutter be incorporated into the extruder - that is perhaps activated via a movement fully to the left or right - perhaps at a particular height? This would I feel solve a lot of the complication with getting a neat tip. I notice the swapper3d kickstarter includes on of these - but it looks a pretty complicated way to do it.
2. Motorised rewinders - I know there are plenty of wind up rewinders - but personally I never really got any of the ones I tried to work, and always found the buffers I tried quite awkward to initially load up, plus change filament. Complicated I know - but could perhaps be based on 4 steppers - controlled from and Arduino connected the Octprint raspberry P1.
RE: Filament cutter at extruder, and motorised rewinder.
Where would the cut off filament go? Cutting it down at the print with MMU loading more materials seems to guarantee it will end up on the print bed and be part of your print?
RE: Filament cutter at extruder, and motorised rewinder.
Both your points are exactly what I've been considering.
I abandoned using the MMU specifically because of all the retract problems, and having now got the AMS can see it's quite an elegant solution. Obviously the gcode would need to add the filament cut, and after changing filament, and additional purge - but that looks possible.
I'm currently looking at modifying the pitstop extruder to include the blade. It would also need a slight x-axis reduction in size to accommodate a blade-'pusher' - (retractable when not in needed for the print).
The purge of cut-off filament will have to go somewhere - something will have to be designed to make up for the lack of a poop bucket. Not helped by the moving z-axis.
A electric rewind on the spool holder also appears a very desirable addition. I suspect this will need a lot of trial and error to get working - still it gives me something to fill my time.
To help make this easier to work on, I'm currently klipper'ing my MK3S and adding a ERCF in place of the MMU
RE: Filament cutter at extruder, and motorised rewinder.
I remember years ago a spool holder with a spring loaded back pull. Ie. no motor/electronics involved. It would keep the filament taught during print and if you cut the filament it would rewind - how much I don't remember, since it was mostly about not letting the filament be loose.
seems to be an example of it.
There would need to be something to control the filament end so it doesn't flip around after the rewind is done, but you should be able to do this without the need of motors/electronics.
A electric rewind on the spool holder also appears a very desirable addition. I suspect this will need a lot of trial and error to get working - still it gives me something to fill my time.