[imtringued]

>the simplest is just mixing filaments, like one mixes paint. The article doesn't spell out the reason it doesn't work, I am curious as to why.

This requires you to control both filaments independently directly at the extruder. Dual direct drive for a single nozzle sounds like an engineering nightmare. The extruder head is going to be huge.

There is also the obvious problem of how to stirr the filament. Printing temperatures aren't hot enough to turn the plastic liquid, they just make it soft enough to drip out the nozzle. This means you can't just feed the filaments at continuos rates, you will have to use a PWM scheme where you extrude the first filament and then the second filament in extremely small discrete increments. That switching will give you the necessary agitation without building a throwaway nozzle that can't be cleaned after a clog.

All of this sounds like it would take at least a year for a well equipped research department to figure out. It's definitely not the simplest solution.

EDIT: https://www.reddit.com/r/ender3v2/comments/ssuw3i/my_crazy_p...

Just the hot end of this extruder costs $70 alone. This is definitely not going to be cheap to do.

[wongarsu]

Minuteman on youtube has a four extruder single nozzle setup for speed printing. He occasionally uses multiple colors, and they basically don't mix in the nozzle. The cross section of an extrusion looks like a pie chart

You would need special nozzle geometry that encourages mixing, and likely much higher temperatures. And any such mixing geometry will trap some filament. Switching from dark to light colors might require purging with meters of light filament to get all traces of black filament out

[MBCook]

Imagine trying to clean that out if it jams.

[MayeulC]

Thank you for the detailed answer. This is an interesting engineering problem.

I wish I had more free time, a gearbox or a 4-way differential can probably be used on the extruder head to control the mixing ratios.

Regarding the necessary research, I can picture it being cracked either by hobbyists, or industrial-scale (patent-heavy) players. I imagine that consumer-facing players such as Prusa do not have the means to heavily invest in R&D.