Sky & Telescope - August 2024 - 75

pLeft: Bracing rods between the chair and the monitor arm provide stability and vibration damping. Springs counter the extra lift of the monitor
stand's internal springs. Lauren moved the nameplate from the top section to the lower section to cover the spliced length of metal pipearm (middle)
added to extend the monitor arm's reach. Right: Lauren added a gyroscope in order to dampen rotational vibrations.
two slabs of thick plywood. Castors on
the bottom let Lauren roll the chair out
to her observing area in the backyard.
She tried using three wheels so they
would act like a tripod, stable on any
surface, but quickly learned that the
chair would tip over at certain angles.
She needed four castors, which meant
she also needed leveling legs to make
sure she had solid contact on all four.
Fortunately, she found a set with builtin
levelers.
That left the binocular-holding arm.
Inspired by her brother Brian's tripodleg
Dobsonian (S&T: Jan. 2023, p. 70),
Lauren first tried mounting a tripod leg
horizontally overhead. That would theoretically
allow her to move the binoculars
forward and back for comfortable
viewing. Bolting the tripod leg to a big
strap hinge attached to the top of the
chair's headrest rods would let her raise
and lower the binoculars for minor
altitude adjustment, while the chair's
tilt mechanism would allow for major
adjustment.
Lauren quickly realized that the
binoculars were just as heavy on the
end of a horizontally mounted tripod
leg as they were when hand-held. So she
positioned the tripod leg with lots of
overhang in the back and added counterweights.
Alas, the weight prevented
the chair from returning to its upright
position. Lauren tried spring-loaded
chest hinges rather than counterweights,
but the springs weren't powerful
enough. And even if they had been,
the weight of the binoculars made the
tripod leg's sliding rail bind, negating its
value as an extendable boom. Plus, having
the hinge behind her head meant
that any up-down motion simply raised
the binoculars away from her eyes. Lauren
tried adding a vertical adjustment
to the end of the tripod leg, but it was a
lost cause.
She finally decided to abandon the
tripod leg idea and raid the monitor
arm from the old chair. With that decision,
her luck immediately changed:
The arm's mounting bracket matched
the chair's arm mount holes nearly
perfectly. She kept the hinge on top
and folded it backward to tie into the
monitor-arm mounting bracket for
additional support, using a threaded rod
between them. She also added a support
piece from the top of the monitor arm's
lower segment to the headrest bolts.
The monitor arm mounts to the
tilting part of the car seat, so the binoculars
stay in observing position no
matter whether the back is reclined or
not. But with the arm mounted behind
the observer there wasn't enough
arm length for Lauren to get behind
the binos. More fixing! So she had to
lengthen the monitor arm with a section
of pipe.
Finally, the bino-chair was ready
to test! Of course you know what's
coming. As Lauren wrote in an email,
" Problems! There was flex in the
plywood itself. There was heartbeat /
breathing / body sway / looseness in the
lazy Suzan - these all worked together
to make very subtle, nearly imperceptible
vibrations. Those vibrations traveled
along the monitor arm like a tuning
fork! The outer end where the binos sat
endlessly moved in tiny vibrations. "
To fix the plywood flex, Lauren
replaced the 12-inch lazy Susan with a
20-incher. She unbolted all the monitor
arm supports and added rubber dampening
at all the connection points. She
doubled the thickness of the binocular
mounting plate. She even added a gyroscope
to provide rotational stability.
Another test night provided more positive
results. As Lauren reported to me
the next morning, " It didn't catch fire. "
It did, in fact, perform quite well. It's
now one comfortable observing chair!
¢ Contributing Editor JERRY OLTION
thinks persistence and ingenuity can
prevail in just about any ATM project.
sk yand tele scope .o r g * AUGUST 2024 75
https://skyandtelescope.org/
Sky & Telescope - August 2024

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