The post below caught my eye recently.

3D Printing
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1

The post below caught my eye recently. It was the detail of analysis and quality of presentation that drew me in initially, but it also gives an interesting insight into possible issues associated with direct-drive bowden style extruders and proposes solutions. You can make up your own mind about the solution or even try it out as the author, “Kevin” kindly shares the design on Youmagine.com also.
https://0x7d.com/2014/07/improved-ultimaker-2-material-extruder/
https://0x7d.com/2014/07/improved-ultimaker-2-material-extruder

2

The idea is interesting.
I’m looking for a way to make the U2 extruder of extruding with a lower minimum feed rate.
However I’d CNC mill the parts and maybe use industrial made gears.

3

I like the idea of using a belt, as you can in theory loose the need to calibrate when you’re feeding a known length of belt. But I’m sorry, I don’t believe your belts are having any say at all over the hobbing in this mechanism.

4

I remember the repman extruder and a giant grip area makes a ton of a difference.