Stepper driven filament spool feeding

One of my problem areas is the extruder needing more filament. And therefore it must over come the friction of a spool holder. Have any of you thought about creating a spool drive that works together with the extruder gearing.

So say for instance the spool isn't located on the 3d printer and it attached to a different place. A stepper motor is tied to the extruder motor, with the correct gear ratios of course. So in theory when the extruder motor pulls 3mm of filament the spool motor will release 3mm of filament and vise versa.

It seems as though it would take a massive amount of load off of the x carriage (Makerfarm i3v). Which would assist in maintaining consistency in print quality.

I've been thinking about this for a couple of weeks and the only thing I can think of that would cause an issue is the parallel connection to the extruder stepper and the spool stepper.

Thanks,

Nathan.

Interesting idea, the major problem i see being that as the filament spool gets used up the filament becomes a smaller diameter around the spool. So somehow you would need to constantly monitor the actual diameter of the filament around the spool and adjust how much the motor sends as a result. I think an easier way would be to have a conventional style extruder motor mounted closer to the spool if that's what your looking for.

One of the problems of the Prusa i3, as you've correctly identified, is that there is an upward force applied to the extruder when it pulls down on the filament. If you push down on the extruder with your finger you can see it move due to the unavoidable flexibility of some of the parts that make up the X and Z axes. All this means that you can get some flexing and unwanted movement of the nozzle whilst extruding, and especially if you have retraction turned on.

The easiest way to deal with this is to transfer the force from the extruder to something more rigid, such as the frame. all you need to do is to get hold of a length of bowden tube, fix one end to the frame with a cable tie and let the other float free. Make sure it's long enough to get from the frame to the end of the extruder in one loop and feed filament through it. The tugging force from the spool is transferred to the frame, instead of the extruder, and you've solved your problem.

Seems like overhead-mounts reduce the drag as much as possible. Maybe even putting bearings on the spool would be easier.