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PeteD
Would a spinning threadless ballscrew work as a filament driver? Or is the diameter of filament too unreliable?
The biggest hurtle I can think of is that variation in the filament diameter would cause the ballscrew to disengage.
I had the same idea, and have made paper sketch of it as a reminder.
The main challenge that I see with it is that the filament would rotate with a single drive.
Another problem is when you reversed the drive to retract the filament, the unwinding would work against you.
Couple of ways to work around this:
It would require two sets that counter rotate with opposing complementary helix angles.
Counter rotating would prevent the filament from twisting.
This would require a belt to drive them.
The drive mechanics is not simple, and the support would be rather large.
To eliminate two counter rotating drives, a knife edge roller could be used to prevent rotation of the filament.
The sharp edge would bite into the filament forming a grove to prevent the filament from rotating.
This would be the easiest to implement.
To compensate for variable filament diameter, spring tension could be used.
But you never know, the amount of compression to drive the filament might be enough to compensate for a variable diameter.