In the late 1980's, Pierre Schwaar was a local legend around the Phoenix telescope
maker's community. His optics were exemplary and his stream of new, innovative
ideas could make NASA take notice. He was a force of nature among telescope
makers, coming up with a 16" F/5 "Telescope-Go-Round", the "Big
Foot" mount and his 8" F/4.2 Binocular Chair. He tinkered constantly,
ever refining and tweaking his inventions to work better and better.
While there was never a doubt of his mirror making abilities, there was some
about his mechanical skills. Some of his tinkering was due to necessity-fatally
flawed details in engineering on the path from his inventive mind and his limited
materials. While his workmanship was high in quality, the design phases were
somewhat limited. Plans went from his head to the cutting table or lathe, without
much consideration given to fine details.
This is so much the tragedy, since many parts from one project went to build
the next. Sometimes it worked, sometimes not.
I found this out in the first restoration of the BinoChair. I spent 5 years,
off and on, working on it, only to see the design flaws take their toll upon
completion. It was my intent then and there to do a complete structural analysis
of the system as a whole, and rebuild the chair to make it more user friendly.
The results of this redesign will be presented here. Click on images to enlarge.
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Pierre's chair in ~1990. |
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First Draft |
Basic Redesign | |
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Current Configuration |
8/12/12 |
The above images show something of the progression of ideas that ran through my head in redesigning the chair. Several options were explored initially, but this one made it to the drawing board. The first draft used the existing chair, base and drive system, while replacing the azimuth box with a torsion box for stiffness and a larger altitude bearing for stability. The blue lines indicate what stays the same and the black indicate the changes.
The second draft show the entire base being replaced after studying the balance characteristics of the first draft. Making the base wider and changing the drive system made it a LOT more stable, lower to the ground and smoother in azimuth. The base design was built over the thanksgiving weekend in 2007.
The current configuration is shown in a CAD drawing. lick for a PDF. A picture taken 8/12/12 is also shown.
The Base
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The basic base, showing the wheel mounted on 2x4's. |
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From the underside. |
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Detail shows screws, but glue was added later. |
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Illustrating the PVC "feet" to be used at the corners. |
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The (mostly) completed base unit. PVC feet are not yet attached, nor is
the ring for azimuth drive cable. |
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Structure from underneath. |
The Table
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Beginnings of the torsion box to support the chair and OTA. |
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Good image showing the lower sheet of 3/4" plywood and the internal
structure that lends the torsion box its strength. The strips are glued
to the sheet, and glued to the top sheet, effectively connecting 25 smaller
boxes of plywood together, rendering them very very stiff, yet not very
thick. |
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Bottom is glued and drying in the truck bed. |
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Each piece was glued and stapled to the bottom sheet to maintain position. |
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Bottom placed on pedestal assembly. |
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Top sheet placed before gluing. |
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Completed torsion box with rollers and steel brackets placed on top. |
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Thin! Rosie and I stood on opposite sides after this dried over night.
We could detect no flexing or tilting at all. I weigh 213 lbs and she weighs...about
half that. :-) |
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Close-up of the torsion box shows the staples and guide lines. |
The Main Altitude Bearing
Fighting problems with a shifting center of gravity, I decided
to rebuild the sides of the chair. The problems were
1) People are different.
2) The chair couldn't adapt to different conditions
3) The chair sides didn't have enough material to mount the
rail solution.
4) The chair sides also had too many holes in them.
Different people have different distributions of differing amounts
of mass. As a more massive person sits in the chair, they shift the center of
mass of the whole system. This causes balance and altitude motor loading problems
as the load shifts. I came up with a couple solutions. One is to counter the
shift by adding weights to the backside of the alt bearings, but this requires
I carry many counterweights, and the whole idea was to avoid that. The one I
chose was to make the chair and OTA adjustable foreward and backward, to reposition
the center of rotation according to the weight of the occupant. I devised a
system of T-rails, with bolts through the alt bearings. Two parallel rails will
easily accommodate the load, but when I went to mount them on the chair, I found
there wasn't enough material there to support them both. I took the chair apart
to figure it out and, looking at the individual chair side and seeing all the
previous holes, I decided to build new ones with sufficient mounting materials
and consistant thickness.
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The new sides, side by side, ;-) showing the new bearings, the star-bolts
that mount to the rails and fasten the bearings to the chair sides. |
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A little closer view of one new assembly. |
I'm extremely excited about the progress made so far. I need to work out how
powerful the motors have to be to drive this thing. I also need it to be damped
so it won't just slide one way or the other, so some form of clutch is in order.
It moves very, very easily in azimuth, and if the rollers were spaced properly,
it would move in altitude easily too. Before I got the rollers installed, I
placed the chair and alt bearings on the pedestal. It rocked like a rocking
chair-nice and easy and stayed put, even when spun in azimuth!
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