Using flexible connectors for dome struts?

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Using flexible connectors for dome struts?

Postby Papa Bear » Thu Oct 16, 2003 12:06 am

A number of years back (long before I ever heard of burning man) some friends and I were experimenting with geodesic dome structures for an outdoor live-action roleplaying group.

One of the more successful variations we came up with was to use flexible connectors to hook up the conduit struts. In our case, it was literally 3 short pieces of old garden hose with a bolt threaded through the middle. Each hose end fit snugly around the end of a piece of conduit, and was secured either with duct tape or with another "pin" through the hose and conduit.

Obviously, that introduced a little play, but the resulting structure was still strong enough to suspend one of us from the top. And we didn't have to flatten the ends of the conduit, which seriously reduced labor. Thought about trying something similar with PVC instead of conduit, but never got around to it.

Of course, we were dealing with smallish (20 foot diameter), low-frequency domes in a much less harsh environment than exists at Burning Man. Has anyone tried something like this on the playa, instead of the usual rigid connections? If so, how well did it work?
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Postby Badger » Thu Oct 16, 2003 6:26 pm

It be really cool if you had a drawing or other diagram to further illustrate what you're trying to describe. Sounds really interesting.
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Postby Papa Bear » Thu Oct 16, 2003 10:56 pm

I'll give it a shot.

To build a connector, cut 3 pieces of garden hose, each about 10 inches long. Lay those 3 pieces against each other like an asterisk. Punch or drill a hole through all three hoses at the center of the asterisk, put a short bolt through with washers on each side, and fasten tight with a nut. You now have your hub:

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If you choose your hose and strut conduit right, the hose will slide tightly over the end of a piece of conduit.

Apart from that, it's a standard dome layout. The difference is that rather than flattening the ends of the strut conduits and bolting them together for a rigid hub, you just cut the conduit to the appropriate length and slide each end into a hub:

Image

There is obviously more play in a hub created this way than there would be with a rigid connection. My guess is that's only a major issue if there's enough play to allow a section of the dome to invert, and so is less likely with lower-frequency domes.

The hose/conduit fit is usually pretty tight, but will pull apart. Duct taping the edge of the hose to the strut adds some strength, but if more was needed you could drill a hole and put a pin through each hose/strut connection (so the pin would have to tear through several inches of hose in order to separate the two).

Any clearer?
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Postby robotland » Fri Oct 17, 2003 5:57 am

you could epoxy a conduit coupler into the hose end- take one of the retaining screws out and cram dat sucka in....
.....fourway couplers would work the same as sixway, but how about FIVEway? Do you just bolt in a short section of hose and bend the others, since the five struts aren't opposite each other?
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Postby Papa Bear » Fri Oct 17, 2003 10:51 am

Actually, if we needed a five-way, we just made a six-way and left one end unused. Kept things simpler, and garden hose is cheap.
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Postby DE FACTO » Fri Oct 17, 2003 11:15 am

Papa Bear wrote:Actually, if we needed a five-way, we just made a six-way and left one end unused. Kept things simpler, and garden hose is cheap.


Wow that sounds prety kinky.

Sorry. Wrong thread.
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Postby Bob » Sat Oct 18, 2003 12:45 am

Made similar six-way connectors back in '99 using three 12-in. lengths of black polyethylene pipe, the cheap flexible kind used for quickie farm and nursery irrigation lines. Flattened the middle of the pieces using a torch and clamp, drilled, and pinned with a bolt, fender washers, and a wing nut.

Used it for a small dome -- scored some 1-in. fiberglass industrial pipe at Urban Ore in Berkeley (stop choking, Badger, I'm sure it was just used for, er, steam, yeah, steam) and 1-1/4 poly pipe for the connectors.

Matching up and lacing through the holes from the poly sleeved over the fiberglass pipe wasn't too much of a pain after the puncture wounds from the rebar tie wire healed. If I did anything similar I'd make up some U-shaped pins from soft steel rod and pin the sleeved pipe through at two spots a couple inches apart. Something like that. Or just give up and buy hardware.

Might slit the poly pipe back an inch or two and wrap tight with wire or 10-mil black vinyl tape.

I see no reason why poly pipe or heavy-duty air hose wouldn't work for a large dome, but vinyl garden hose might soften too much in the heat.
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Postby Grover » Mon Dec 01, 2003 10:25 am

Bob wrote:<snip> but vinyl garden hose might soften too much in the heat.


Standard (cheap) garden hose does soften, but has survived a week when being used for a 16ft diameter dome. In hindsight I would use larger diameter, heavy duty black hose. I'd also use conduit instead of PVC, stick the conduit inside the hose and add hose clamps.
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