Sky and Telescope - April 2016 - 64

Gary Seronik
Telescope Workshop

Oltion's Equatorial Platform
This low-proﬁle mount provides motorized tracking for large-aperture scopes.
I've long felt

the ideal deep-sky machine is a bigaperture scope on an equatorial mount. Sure, most of us
adapt readily enough to pushing our Dobsonians along to
keep a target in the eyepiece, but there's no denying that
it's much nicer to be able enjoy the view without the fuss.
Thanks to the advent of equatorial platforms, we can
luxuriate in hands-free observing without the weight
and bulk of a regular German equatorial mount. But the
problem with many platforms is they usually add several
inches to the height of the eyepiece. That sounds minor,
but it can be the diﬀerence between needing a ladder or
not - and that's a big deal.
Over the years this magazine has featured several
equatorial platforms, but I can't recall seeing one as
minimalist and low-proﬁ le as this unit by Oregon ATM
Jerry Oltion. Many readers will recognize Jerry's name;
he's contributed several innovative ideas to these pages
over the years. So, I wasn't surprised to see him come
up with such an elegant equatorial platform to carry his
20-inch Dobsonian and 12½-inch bino scope, which was
featured in the January 2015 issue, page 68.

Curved north bearings

Idler bearing
Drive
roller

Drive
motor
Bubble
level

JERRY OLTION

South pivot

Oltion's minimalist equatorial platform provides motorized tracking without adding signiﬁcant weight or eyepiece height. The
mount's stepper motor and electronics were purchased online.

April 2016 sky & telescope

"I'd been thinking about building an equatorial platform for my big scopes, but I didn't want to add much
height to them, nor did I want yet another bulky, heavy
component to carry around and set up," Jerry says. That
desire fuelled his imagination. "I began by ﬁguring out
what parts of the mount were absolutely necessary, and
then leaving out the rest."
Jerry took his cue from the ﬂex-rocker concept
pioneered by fellow Oregon ATM Mel Bartels and others. (See S&T: August 2004, pg. 133 for more.) In a ﬂex
scope, a Dobsonian's traditional rocker box and base are
replaced with a ring and low-proﬁle rocker assembly that
allows the altitude and azimuth bearing points to lie
atop one another, reducing the need for stiﬀ, heavy components. The resulting lightweight conﬁguration adds
minimal height to the eyepiece position when pointed
towards the zenith. Jerry realized that the same principle
could work for an equatorial platform. The ground ring
provides plenty of stiﬀ ness - the ﬂex equatorial platform merely holds the bearings in the right place.
"A project like this isn't nearly as diﬃcult to build as
some would have you believe," he notes. But there are a
few tricky bits. As the photos here illustrate, Jerry's minimalist platform consists of three main subassemblies.
First there is the ﬂex ring, which served as the scope's
original base. Next is the T-assembly that holds the
mount's bearings and drive motor in position. Last is a
pair of wooden arcs that functions as the mount's northaxis bearing runners. The arcs attach to the underside
of the ﬂex ring via pairs of smooth rods that slide into
matching sockets, and ride on matching bearings (one
drive bearing, one idler) on the platform base.
The speciﬁc angles for the south pivot point and bearing surfaces depend on latitude. "It occurred to me as
I was building the platform that the design lends itself
to easy modiﬁcation for diﬀerent latitudes and/or scope
sizes - just change the curve of the runners and the
south pivot point's distance from the edge of the ring"
Jerry says. "A person could have several sets of runners
and pivot mounts for various latitudes and scopes."
Although you can derive the dimensions and required
angles for the platform mathematically, Jerry took a
diﬀerent approach. "I wound up ﬁguring out the proper

Sky and Telescope - April 2016

Table of Contents for the Digital Edition of Sky and Telescope - April 2016