A model of the helix tubing system with supporting structures made from transparent tubing.

We are privileged to participate in a helical bend for a children’s museum in Baton Rouge. More later as this develops. The helix (hexagonal) has a 96″ radius and composed of (CAB) cellulose acetate tubing (4.125″ID).

 

A design drawing of the large helix tubing system for the children's museum.
A model of the helix tubing system connected by wire to support scaffolding.

Model 1 and support circle.

A fragment of a design schematic for the tubing system and support structers.
Model of the helix system with support circle and scaffolding.
Diagram of the support circle with hexagonal lines.
Computer design plan of the helix bend and support ring
A long grey tubing bend on supports

Ideas on suspension. There is a position along the bend where you could suspend it and have very little tendency for it to rotate or sag. We need to find this point on the bends. The key is to find this point on a 60° bend.Take the bend and with one end on the ground pick up the other end it will tend to rotate so that the bend hangs down. Next with one end on the ground,lift it just above the middle, the top end will try to point down. It will swivel in the opposite direction to the first experiment. There is a position between half way and the end where it has no real tendency to go either way, but will still swivel if you let it as that is a metastable state. But restraining it from twisting requires the merest touch. My guess is that position is between one quarter to one third of the way from the top end. That is the ideal suspension point.

Holding a PVC model of the helix tubing system

The reaction on the couplings is at a minimum and it will be the easiest to assemble as it will twist whichever way you want to align the tangents really easily. It is probable that the supports from the roof will be rotated in plan view about15-20° from what the drawings show.

The effect of the shuttle or carrier. Newton’s laws — or action and opposite reaction. It won’t change speeds on the bends unless the friction is really high. The air velocity is going to be the main thing that governs the speed and so changing the tangents does not seem to be needed.

A simple wire from the suspension to some point on the ceiling inside of the helix would resist swinging movement. The suspension would then be a triangle of a vertical strut and an angled wire. Angled in towards the center as the centripetal force would be directed out from the center. If the helix did sway we may have to allow the horizontal legs to have a bit of flexibility. Maybe just pin the coupler with a little slack rather than glue it tight.

The long tubing bend supported by wooden blocks
The long tubing bend on the shop floor

Banking Carrier on a straight section.

Suggestion for 12″ tangents on 60 Deg
Below is the size bend that we want to propose. It has 12″ of tangents which gives us ample wiggle room to install, but the majority of the helix will be curved. We believe that this will make travel smoother than the tight radius bends with longer tangents.

A computer made design plan of the tubing bend
A computer made design plan of the tubing bend

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Here are the main drawings with some of my observations and questions.

A labelled design plan of the helix system looking down from above
A side view of the labeled design plan of the huge helix tubing system.

I know that we discussed the dotted line bend, but I still need clarification on the diameter and radius.

I would like to know who is responsible for making sure that the helix lines up to the pneumatic boxes.

A labeled design plan of the huge helix tubing system seen on a computer screen

Testing of the 24″ Radius input and exit bend.

 

February 2017
And so it begins!!!! The first two sections.

The first two sections come together. They are in a split coupling with just wood supports for a rise. The rise angle is not important at this time. We just need to get the sections placed together. Altogether we need 10 sections for the 1.5 tiers for this project.

The long tubing bend on the shop floor

Here we have the third section. Since these are all 60 Deg, we have 180 degrees and half of the circle.

Now, we can test the diameter. The Helix was designed with 12″ tangents and a 76″ Center Line Radius, so we are hoping to get a 16″ diameter. Since we have long tangents, we can modify the entire tangent by simply removing some tangents along the way.

Bingo! Spot on. It’s nice when things work the first time (or so we think). We have a 16″ Center Line.

The Helix is flexible and we’ll see how it winds around.

But first, we want to see if the carrier travels smoothly.

The long tubing bend supported by wooden blocks
Employees measuring the distance between the two ends of the long tubing bend

When assembling the helix start out with the slit couplings and then after the helix is complete, replace the slit couplings with un-slit couplings and use a solvent weld.

Tube sections joined by a solvent welded sleeve
A sleeve solvent welded onto a tube

And the assembly.

 

Testing the Helix.

 

When hanging the helix, find the metastable position of each section.

Demonstration of Meta-Staple position for support.

Using a rope tied around a tubing bend to lift the tube and find its meta-stable position

First and last bends have a 6 Degree bend before the tangent. This compensates for the pitch of the bend Arctan(Pitch/Pi*D). With a diameter of 192″ and a pitch of 60″ it comes to approx 5.6 Degrees.

This works out to be 5.8° for a true helix lay angle and it’s 6.4° for the combination of 90° bends at 90-inch radius.

 

The long six degree tubing bend on the shop floor

The formula is Arctan(15/(root2 x End to End of bend). The root2 coming from the 45° angle of the tangent from the end to end line.

The neatest way to handle that would be to make one ‘tangent’ longer on the first and last bend and put in a bend of this amount at the end such that it would stick up when the bend was laid flat, but this is possible but impractical. And we would need opposite hand tangents to be modified for the two ends which would then transition to the horizontal tube.

And . . . the test run.

The final part is to make a 2″ saddle on the 24″ Radius bends. The trick is that the saddle comes directly on the arc.

a tubing saddle added to the arc of a tube bend

And the precious supervisor.

 

A short section of tubing ready to be attached to the tubing bend to function as a support saddle
Pudge the dog laying behind a model of the helix

Suggestions for support ring.

 

Sections of tubing stacked up on Busada's storage shelves
A design plan of the helix showing possible supports for the tubing system
A design plan of the bend with markings and measurements
Design schematic of the support circle for the helix tubing system
Computer design plan of the long bend with measurements

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