Sky & Telescope - July 2021 - 72

ASTRONOMER'S WORKBENCH by Jerry Oltion

Make Your Own
Push-To Scope
Install digital setting circles in thin air.

she's owned - ﬂocking the inside of
the tubes, making extended dew shields
and shrouds, installing cooling fans,
and adding manual setting circles.
She even converted her 10-inch Orion
IntelliScope to send its position signals
to a tablet running SkySafari to make
a push-to scope with visual feedback.
Lauren liked the latter setup so well
that when she purchased Mel Bartels's
famous 13-inch Zip Dob (S&T: Jan.
2012, p. 62), she wasted no time adding
digital setting circles to that, too.
There was just one little problem:
The Zip Dob lacks any physical horizontal or vertical pivot points to attach
the encoders to. The scope sits on a ﬂex

rocker and ground ring, so there's nothing but space where the azimuth pivot
bolt would be on a traditional Dobsonian scope, and it uses its own open
framework for the altitude bearing, so
there's no central point there, either.
Lauren reasoned that there was still
a center of rotation in both the altitude
and azimuth axes - they were just virtual. That meant all she needed to do in
order to install encoders at those pivot
points was to make them real, solid
points instead.
It was a fairly straightforward
progression from there. Lauren taped a
piece of paper across the Zip Dob's side
and tilted the scope up and down a few
times to ﬁnd the point that didn't move.
The azimuth axis was even easier: Set
the ground ring on
a thick plywood
base and spin the
ﬂex rocker around
to ﬁ nd the center
of rotation.
Once she'd
found the points
where the encoders needed to go,
she had to build
something to hold
the encoders in
place. The azimuth
axis was already
half done with the
plywood base, but
it needed an arm
reaching inward to
W Lauren Wingert
put digital setting
circles on her scope
despite the lack of
solid pivot points to
mount them on.

72

J U LY 2 0 2 1 * S K Y & T E L E S C O P E

S The encoders are mounted at the ends of
arms that reach from the telescope's framework to the center of rotation on the altitude
and azimuth axes.

the center from the telescope, too. And
the altitude axis needed both an arm
and a cross-member spanning from side
to side of the scope.
Lauren faced an additional complication: She didn't want to drill holes in
Mel's classic telescope. So she designed
everything to attach with clamps
instead. She came up with three structures: a board that spans the altitude
axis, a shelf that clamps to the back of
the telescope, and an arm that reaches
inward from the shelf to the center of
the altitude axis. The shelf holds the
battery and the encoder's Bluetooth
transmitter, and it supports the arm
that reaches out to the azimuth axis's
center of rotation.
After assembling it for the ﬁrst time,
Lauren found there were minor imperfections in how the scope rotated on
its ground ring. That required a ﬁ x that
would prevent encoder stress or damage.
The solution: Put a slip joint in the arm
holding the encoder so it could shift
slightly as the telescope moved. The
altitude arm required similar ﬂexibility,
which a simple notch that held it to the
shelf provided. The encoder shaft supported the arm's weight, so that notch
didn't need to be tight.
Lauren used DobsonDream4 encoders
from the Ukrainian company AstroGadget (astro-gadget.net). She bought
the version that has 4,000 pulses per
revolution. The controller that interprets
the encoder pulses communicates via

L AUREN WING ERT (2)

LAUREN WINGERT IS A GADGET
GIRL. She has modiﬁed every telescope
http://www.astro-gadget.net
Sky & Telescope - July 2021

Table of Contents for the Digital Edition of Sky & Telescope - July 2021
