I'm curious if the whole tube needs to move, or just the scoops. At what point do you think the friction against the unmoving tube, would overcome the benefits of not needing to move as much material?,(reply>), @GildedBear Nope, you are missing the principle. It keeps working even when the supply at the bottom runs out,(reply>), I would guess that just the scoops need to move but setting it up that way would require a bearing and seal between the two parts and that would allow particulates to get into the seal and potentially the lubricant to get into the particulates.