Idea for extruder reliability improvement on large printers

I have been waiting patiently for user feedback on the large scale Gigabot printer, and it looks like the first full review has finally come in. [canprint3d.com]
Of course a giant print is going to take a lot of time, so I am not concerned with the reviewer's contention with print time. My worry is the reliability of the extruder during such large and time consuming prints. The author writes: "Another symptom of the free-hanging wire issue and the large build surface is that the extruder had intermittent difficulties in pulling the filament through the long winding filament guide tube. The result was that several of our test prints failed mid-way due to under extrusion. This would be devastating were it to occur during the large prints that one would expect to be using the Gigabot for."

I wonder if reliability could be improved by reconfiguring the filament feed setup so that the spool is mounted a foot or two up over the center of the printer, with a "primer" extruder motor that pulls/ pushes the filament into a teflon tube that leads to the actual extruder motor above the hot-end. The first motor would move in exact conjuction with the second, and would simply act as a helper or backup for pulling the filament into the extruder.

thoughts?

I don't know how much this would effect things. I am going to be running a machine with a 6'-6" tube that runs to a direct drive system. They could also try changing the tube to something with a lower coefficient of friction. I have run my Ultimaker for 70+ hours straight doing 50 micron prints and had no issues with those prints, but that is a different machine.

It seems like a second motor would complicate things. If one begins to miss steps or there is a clog on one but not the other it could be bad.

You are right though, moving the filament to a higher point on the machine to shorten the tube would help out greatly. Another option would be to change the style of hobbed or knurled bolt being used to something with more grip so that loosing pull would be less of an issue.

The machine they are working with is not quite big enough to suggest going to a direct pellet to filament drive system like the Kamermaker, but it is a possibility.

Why not connect the motors similar to a dual motor z axis where they both move at the same time and same rate?

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greghoge.com

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I would box it, as a bigger heated bed has more surface, it cools down faster so it asks for even more power.

Second, it seems like a good idea to size-up the nozzle, to you can make prototypes faster.

Filament printing is meant for prototyping, if you want to build sculptures, I advise you to look at a big DLP printers