An exciting element for any knex ball tower.
Video link at http://www.youtube.com/watch?v=XTc5rsT-Lfg

Step 1: Frame

Construct a frame using 12 grey rods and 16 blue connectors. Alternatively you could use purple connectors depending on the situation.

Step 2: The Crossbars

Add the crossbars using grey rods, grey connectors and lots of spacers. Put 2 connectors on each end of the rod and add the spacers as shown in the diagram. Spacing is crucial so if you are using something smaller than a standard knex ball you should use less spacers.

x grey rods
2 grey connectors per rod
lots of spacers

Its a bad photo, yeh?

Step 3: The Crosspieces

Add the crosspieces in the pattern 3-2-3-2....

Step 4: Compiling the Crosspieces

Slide the crosspieces together so that they only just touch. Ensure that the crosspieces all connect together with the pins locking into the rectangular holes in the corresponding pieces as shown in the picture.

(Thats a completely useless photo. I don't know how enyone could make comething comprehensive from that)

Step 5: Tubing

Wrap the tubing into the spiral ensuring that all the connector pins are used. When you reach the top wrap the tubing around the uppermost crosspieces so that the track is on roughly 45 degrees to allow easy entry for the balls. In the picture I have added an extra length of tubing to make the track smoother as well as two extra crosspieces for support.

approx 1m tubing required

(Is it bending? YES. If you can, use some lss-stiff tubing (like the orange stuff))