Australian Sky & Telescope - April 2016__

72 AUSTRALIAN SKY & TELESCOPE APRIL 2016

I

’ve long felt that the ideal deep sky machine is a

big-aperture scope on an equatorial mount. Sure,

most of us adapt readily enough to pushing our

Dobsonians along to keep a target centred through 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 quite a few centimetres 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-profile as this unit by Jerry Oltion.

You might recognise 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 50-cm

Equatorial platform project

This low-profile mount provides motorised tracking for large-aperture scopes.

Dobsonian and 32-cm bino scope.

“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 amateur telescope maker, Mel Bartels,

and others. 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 realised that the same

principle could work for an equatorial platform. The

ground ring provides plenty of stiffness — 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 north-axis 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

Jerry Oltion’s minimalist equatorial platform provides motorised tracking without
adding significant weight or eyepiece height. The stepper motor and electronics
were purchased online.

JERRY OLTION

Curved north bearings

Idler bearing

Bubble

level

Drive

Drive roller motor

South pivot

Gary Seronik

Telescope Workshop