Building the Octagon Pt.27. Pier tension?

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Could the pier remain well isolated but safely maintained upright by several of my collection of punctured, narrow, racing bicycle, inner tubes? Each reaching out to anchors under the obs.floor? The lateral forces required are really quite small. Flexible restraint, even when the massive mounting and OTAs are present,  is well within the capacity of a few of these stretchy inner tubes. 

The individual loads on multiple, flexible lines would be very low. Not to mention at right angles to the normal mode of footfalls on the observatory floor.

Have I accidentally hit the creative jackpot for tall pier support? The tubes could easily be linked to stretch right out to the walls of the obs. itself while safely out of the way beneath the observatory floor. Such long chains would have little chance of short-circuiting the pier isolation.

If you wanted a smarter system then there is bungee cord. Probably more flexible and providing even better isolation from building vibration. I bought a load of cheap bungee cord to laminate the cardboard tubes for the 10" f/8 OTA. I'd almost forgotten about that.

The rain should have ended by tomorrow so I can experiment on the restraint requirements and vibrational feedback. Fixing a mirror to the pier and firing a laser pointer at it should provide some useful insight as I hop about on the the Obs. floor. Though the "clog dancing" may be a bit premature until I complete the floor.

The real question is whether the large mass will, by itself, constrain minute vibration at the eyepiece. It is difficult to conceive of any useful damping system which would work over tiny amplitudes at VLFs. Air, fluid and frictional damping work best against considerable movement. The whole thing could, might, will oscillate freely at its natural resonant frequency. Likely at some small fraction of a Hertz.

A tension system would be incredibly easy to implement. It would be safe, practical and easy to change over a large range of tension. It would be extremely convenient if it worked. Being underfloor where there is no traffic. Easily reached from the ground floor with no external factors. Perhaps I should build a test platform on top of the poles to simulate the heavy mounting? Pile bricks or slabs and keep adding more tension to find a nice balance. If there is one.

The system is essentially an inverted pendulum. Well known for its instability. However, if it is restrained to tiny variations each side of perfectly vertical, then the restoring forces required are minute. I could not believe how easy it was to keep four very heavy poles upright by light finger pressure alone. The same posts which were so difficult to lift off the ground and poke through the small floor aperture, had suddenly become essentially weightless. I was an inverted juggler balancing my cane on the tip of my finger from above. Had I found the perfect, vertical balance point I could have restrained the massive pier with a single length of sewing cotton. Perhaps pole-opposed magnets would do the job? But why get involved if rubber bands can mange the job with much less effort?

I could easily spread the feet of the poles much further apart. But at the cost of much greater inconvenience down on the ground floor. Any form of triangulation of a narrow pole to widely spread feet will eat up valuable floor space. Much of the useful volume of the downstairs room would be heavily compromised. The same holds true for sloping guy lines if they cut through the room. Any such additions must also be completely free of the building itself.

Click on any image for an enlargement.

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