From: Patrick Salsbury (salsbury_at_sculptors.com)
Date: 03/04/00
Message-Id: <200003050304.TAA21882@bootstrap.sculptors.com> Subject: Re: ball connection Date: Sat, 04 Mar 2000 19:04:21 -0800 From: Patrick Salsbury <salsbury_at_sculptors.com>
> > Darrel Mand was asking about designs for a universal hub.
> > I've been doing some 3D computer modelling on just this problem, and
> > have a design worked out for 2 hubs (5 and 6 strut) that should
> > handle all angles for 3, 4 and 5-frequency geodesics.
>
> I like your hub designs, though I wonder about the "spindly" legs on
> the autonomous house. Center of gravity, and all that...
Yeah, that's one concern of mine. As a conceptual model, it
definitely conveys the idea to people of things that can move and
adjust to most terrains. I may go with something more like a
backhoe-like articulated arm, with an "elbow" or two on the way to
the ground. Then the house would look even more spider-like, but the
center of gravity could sit lower.
I've not yet put that design into work on the modeler,
though.
> Back to the hubs. Something similar to your design would be producible
> with relative ease, with a simple drill press. In fact, it's not totally
> dissimilar
> to the old Tinkertoy sets I play with occasionally.
>
> An idea. Could the design be modified slightly (no ball end, perhaps?)
> to
> make its low tech manufacture a bit easier? No need for me to turn
> strut ends on a lathe, for example. Could, for example, a simple groove
> near the end of the strut, produce a similar "locking" effect?
Actually, a groove was my first design, but it doesn't allow
for full range of motion on the hub.
For the hub to work in all positions on 3, 4, and 5 frequency domes,
the strut needs to be able to move side-to-side (face angle) in a
range from 54 to 72 degrees (for a 5-point hub. A 6-point would stay
much closer to 60 degrees).
The strut would also have to move in-and-out relative to the
geometric center of the dome (axial angle) in a range from 78-85
degrees. None of the struts meet the hub at 90 degrees, or it would
be a plane, not a dome.
In order to get the full range of this biaxial motion, you
really need a ball-and-socket sort of connection, or some sort of
difficult-to-manufacture and prone-to-breakage, complicated
double-hinged swivel / gimbal arrangement. (Not only hard to
manufacture, but hard to type! ;^) )
> Your design is nearly perfect for mass manufacture, with sophisticated
> equipment. But it's lacking just a bit, for easy prototyping in a home
> workshop.
Thanks. That was my intent (to make it easy to mass-produce,
not to make it hard for hobbyists.) Too often, I think that much of
housing technology hasn't really advanced because there is so very
much craft involved in building. Especially in domes.
Joints are hand-cut, walls are hand-spackled, etc. When you look at
the ubiquitous parts of buildings, such as nails, screws, and 2x4's
or other milled lumber, they're mass-produced. That makes them easy
to use in most situations, with custom-fitting only needed sometimes.
(Compare and contrast with hand-hewn log-cabins or hand-carved wood.)
No offense to any of the dome-builders here, but even current
commercial systems use 2x4's and such. They are almost-literally
trying to fit square pegs into round holes. Those building materials
were not designed from the start for the triangular construction of
geodesics, so there's a huge labor investment in 'fudging' things to
fit, hand-cutting sheetrock, hand sealing all the weird angles, etc.
This design, by design, is intended for domes. A variety of
domes, but specifically domes. It won't work in square houses, but
should work perfectly for what it's designed.
> The hubs are *almost* manufacturable on my drill press, as is. Forstner
> bits drill a large diameter hole, with a flat bottom. The "flared"
> collar is
> achievable with a countersinking bit, though on the scale we're talking
> about it would require something custom.
Yeah. As noted, it's really not designed for us to do on a
small scale. It's designed to hand to a manufacturer and say "I need
10,000,000,000 of these in the next year. Can you do that?"
> I'm not in the position to redesign your hub/strut combination, but you
> are. It would only require minimal change to your basic design, for
> ease of home manufacture. I'm just not positive what those changes
> would have to be. (Think of a *basic* woodshop) The main problem
> is in the strut ends -- ball ends are difficult for me to produce.
>
> Hmmm...wonder if standard dowels, inserted into wooden beads,
> would work for a strut's ball end?
>
> -- Chuck Knight
Now you're on to it! That's exactly my intention. There are
already pre-milled metal balls used in certain types of furniture
construction. I know a few architects who work with these to design
furniture that's modular and extensible. It's all rectilinear-based,
so the balls are usually milled in 3, 4, 5, or 6 areas with threaded
holes that the struts can screw into, depending on it if needs to be
a corner, edge, or whatever.
Ken, do you or Daniel have a website showing some of these
materials? A picture is worth a thousand words...
For these hub designs, I'm thinking of a similar milled-ball.
Probably metal, perhaps composite, if we can manage it. Pre-drilled
and threaded with one hole, so that it can cap a standard pipe that
we also have cut to whatever specific lengths are needed. Then you
just screw the ball onto the end, and viola!, instant strut.
You have to think in statistical numbers to properly
appreciate the scale and magnitude of these houses in proper
production. Thus, keeping each component as simple and modular as
possible allows us to use standard components, and perhaps farm out
the manufacturing to multiple companies, so we have redundancy
and can scale orders to the capabilities of each shop, large and
small. So you may have a ball-end maker (or 7 of them), a strut-pipe
maker (or 7 of them), a hub-maker (or 7 of them), an aerogel-panel
maker (or 7 of them), and octet-truss floor makers (or 7 of them).
Having simple designs that anyone can make allows you to
contract out to get the bulk supplies needed, and also doesn't
cripple you if one supply plant decides to go on strike, such as
happens with GM every few years.
Here are a few numbers to help you think statistically about
the magnitude of this future operation.
I've calculated that 10,000,000 houses per year is a good target, but
it's not actually enough to even hold steady with the number of
homeless people currently in the world (about 400,000,000) and the
number expected in the next 30 years (another 400,000,000, meaning
we'd need 40 years at 10,000,000/year to take care of today's
homeless, and we'd have that number again within 30 years.)
For reference, and again, to underscore the magnitude of this
project, here's a comparison with the total number of new housing
starts in the US, as per Census Bureau info at:
http://www.census.gov:80/indicator/www/housing.html
(The Census has some VERY cool info! I'm quite happy to have access
to it now via the web. When I last filled out my forms 10 years ago,
I wasn't so sure about it, but in just the last 5 years, we've built
a huge infrastructure to access all that data, so I'm glad it's
there. Just got my new forms a few days ago, so I'll be much happier
to fill them out, this time. :-) )
Here's a quote from their page, dated Feb 16, 2000:
---------
Privately owned housing starts in January were at a seasonally adjusted annual
rate of 1,775,000, according to estimates reported today by the U.S. Commerce
Department's Bureau of the Census. This is 2 (+/-6) percent above the revised
December 1999 rate of 1,748,000, but 2(+/-7) percent below the January 1999
rate of 1,804,000.
Single-family housing starts in January 2000 were at a rate of 1,396,000, this is
2 (+/-6) percent below the December 1999 figure of 1,426,000. The January rate
for units in buildings with five units or more was 350,000. The January rate for
units in buildings with two to four units was 29,000.
---------
So, while the US rate is (currently) about 1,775,000 houses per year, even
10,000,000 per year won't solve the global housing crisis...
10,000,000 houses / 365 days per year = 27,396.26 houses per day,
including weekends and all holidays
27,396.26 houses per day / 24 hours = 1141.5 houses per hour, every
hour, every day.
1141.5 houses per hour / 60 minutes per hour = 19 houses per minute.
As you can see, we're going to need a LOT of help, and I'm
not at all worried about competition. This market is much wider open
than the computer manufacturing market. I'd estimate that at least 1
out of every 3 people on the planet NEEDS some sort of improved
shelter just to get them to "adequate" status. You can't make that
argument for computers.
More numbers:
A 4-frequency geodesic sphere will have the following
component parts (provided my calculations are correct! :-) ):
Hub part counts are based on my hub design at
http://reality.sculptors.com/~salsbury/House/
162 hubs (162 hub tops, 162 hub bottoms, 162 bolts to fasten)
(150 6-point hubs, 12 5-point hubs)
480 struts (960 strut-ends)
320 panels
This means, just for the basic manufacturing of the shell
units in the house, we're going to need these types of numbers for
our components:
1,620,000,000 complete hub units
4,800,000,000 struts
9,600,000,000 strut ends
3,200,000,000 panels
...Every year. Not to mention spares for breakage,
manufacturing errors, etc.
This is not a small undertaking. That's why I'm trying to
keep the designs simple and easy to build. It's also why I'm not
focusing on how to make it easy for the home hobbyist, because that's
not the path that will allow us to make good headway. Rather, I think
making it easy enough for every person who's got a machine shop (and
some decent quality-control processes) to get involved and make some
of these is the way to go. I know of few (if any) companies that can
manufacture 1.6-9 billion units of something on their own. (But I bet
many of them would love a contract like that!)
Remember also that those numbers are per-year, and that we're
looking at 40-year sustained order loads, just to deal with today's
homeless issues.
Hopeless? Nah... I think "exciting" is a better word. (Not to
mention "challenging"! ;^) )
Pat