University of Canterbury, New Zealand
This LEGO Great Ball Contraption (GBC) module uses a true Double Helix Archimedes Screw to transport the balls. It uses slides (6 x 12 x 8 studs, 11267) for its screw. It works very reliably and does not jam. There are some more photos in my Flickr album.
This LEGO Great Ball Contraption (GBC) module uses Nicolas’ (Nico71) ball pump to push the balls up through the tower. The balls then roll down a rotating double helix that is made from LEGO slides (6 x 12 x 8 studs, 11267). It works very reliably and does not jam. There are some more photos over at Flickr.