Mathis Instruments MI-500 User manual

Page 1
Setup Guide
MI-500, MI-750 & MI-1000
Fork Mounts
Mathis Instruments
www.mathis-instruments.com
January, 2016
MI-750/1000 Fork Mount

Page 2

Table of Contents
Introduction 5
Mount Components 7
Polar Base 7
Base Plate 8
Rocker and Rocker Base 8
Polar Cone 9
Equatorial Forks 11
Telescope Plates 12
Altazimuth Fork Mounts 13
Azimuth Base 14
Altazimuth Fork 14
Electronic Controls 15
Servo II 15
AstroPhysics GTO4 17
Installation 19
Uncrating the Mount 19
Hardware 19
Base Plate and Pier 19
Rocker Base 20
Fork Hub 20
Fork Arms 21
Installing the Telescope 22
Slip Clutch 24
Adjustments 27
Azimuth 27
Altitude 28
Balancing the Mount 29
Orthogonality of the Telescope 30
Polar Alignment Using Polaris 32
Polar Alignment by Star Drift 33

Maintenance 35
Lubrication 35
Cleaning 36
Worm Plate 36
PEC Sensor 38
Home Sensors 39
Renishaw Encoders 41
Cold Weather Operation 44
Electronic Damage 44
Technical Support 45

Page 5
Introduction
Congratulations, and thank you for purchasing your telescope mount from Mathis
Instruments. We are confident that the design and construction of our mounts
will serve you well in your astronomical pursuits. This manual will explain the
components, setup, operation, and maintenance of your equatorial or altazimuth
fork mount.
Each of our fork mounts is available in an equatorial or altazimuth configuara-
tion. Our family of mounts includes the following:
Model Application
MI-500 12-16 inch telescopes
MI-500 /750 14-18 inch telescopes 500 base with 750 fork
MI-750 16-20 inch telescopes
MI-750/1000 18-20 inch telescopes 750 base with 1000 fork
MI-1000 20-24 inch telescopes
MI-1000/1250 24 inch telescopes 1000 base with 1250 fork
Our mounts are also available in a German equatorial configuration. The
assembly and operation of fork and German mounts are very similar. In
most cases, the size and weight of these mounts make it very challeng-
ing to transport the equipment to a remote site, and in general, they are
designed to be permanently housed in an observatory setting. Only the
MI-500 is light enough to be transportable, provided you have sufficient
determination and strength. These instructions focus primarily on observatory
installations.

Page 6

Page 7
Mount Components
Polar Base
Each equatorial fork mount has a polar base as one of the key components.
The polar base contains the right ascension axis, the worm gear drive, and the
servomotor that provides slewing and tracking to follow celestial objects across
the sky.
The polar base has the following parts: the base plate, the rocker base, the
rocker, the polar cone, the right ascension (RA) axis, the RA worm gear and worm,
motor assembly, and the gear casing with removable covers. The diagram below
illustrates these parts of the polar base.

Page 8
Base Plate for MI-750 Mount
Base Plate
The base plate attaches to the top
of your observatory column or pier.
There are different ways to do this,
but the most common is to put bolts
through the base plate that screw
into holes on top of your pier.
Alternately, the bolts can pass
through the base and the pier with
nuts threaded on to the end of the
bolts.
In most cases, we customize the
holes in the base plate to match the holes in the pier. Make sure that the base
plate is securely fastened to the top of your pier, since it is the foundation of the
mount and telescope.
The base plate and rocker base for the MI-500 and MI-750 mounts are round,
whereas the MI-1000 mount has a rectangular base plate and rocker base.
Rocker and Rocker Base
The base plate has a small push block on the north side. For the southern
hemisphere, this block is on the
south side. The rocker base is bolted
to the base plate and fits over this
push block. There are two recessed
set screws that push against this
block. During polar alignment,
these set screws are used to adjust
the azimuth angle of mount. One
can adjust the azimuth by about 4
degrees to either side of center.
The rocker is attached to the
bottom of the polar cone It has a machined curve that exactly matches the
concave curve in the rocker base. The polar cone and rocker sit on top
of the rocker base and are secured by four stainless steel bolts.
These four bolts pass through the slotted holes on the sides of the rocker and
screw into threaded holes in the rocker base. The rocker is bolted to the under-
side of the polar cone at the factory and should never need to be removed.
Azimuth Adjustment Screw in Rocker Base

Page 9
On the back side of the rocker base
there is an altitude adjustment
screw. This screw is used to push
against the bottom of rocker. This
will change the altitude of the polar
assembly to match the latitude of
your observatory.
When you place the rocker and
polar cone on to the rocker base, first
apply a small amount of grease
on the convex and concave mating
surfaces. This grease will allow the
rocker to slide easily on the rocker
base and will facilitate making
changes in the altitude during polar
alignment.
With the polar cone and rocker
bolted to the rocker base, the entire
weight of the telescope and mount is
supported across concave surface of
the rocker base.
The rocker-base of the MI-500 and
MI-750 mounts has the azimuth adjustment screws on the north side of the base.
The MI-1000 mount also has azimuth adjustment screws on the north side of
the rectangular rocker base, with the altitude adjustment is on the south end.
Polar Cone
On the front of the polar cone is the gear casing. This casing encloses the right
ascension worm gear, the worm, the motor assembly, and the casing covers. The
casing itself is rigidly fixed to the polar cone and should never need to be re-
moved. It provides the mounting surface for the worm assembly and servomotor.
The gear casing cover consists of two parts. The circular cover at the top of the
casing provides protection for the worm gear and should be left in place except
when cleaning is needed. The lower area of the casing is covered by a smaller
trapezoidal plate that can be removed whenever lubrication or when adjustment
of the worm and motor assembly is needed. You can easily remove this cover to
inspect the servomotor and drive gear.
Rocker and Rocker Base for MI-1000
Altitude Screw in Rocker Base

Page 10
The polar axis of the mount pass-
es through the polar cone. It is
supported by a large shielded bear-
ing at the top of the cone and a
smaller guide bearing at the bottom
of the cone. A black anodized nut is
threaded onto the end of the polar
axis and serves to provide a modest
thrust load to the bearing assembly .
The top surface of the polar axis is
where the fork assembly is attached.
For German mounts, the declination
assembly bolts to the top of polar
axis.
The picture at the right shows the
inside of the gear casing with
the worm gear, worm plate, and
servomotor. Depending on the
electronic control, the motor shaft
drives the worm shaft using pulleys
and a timing belt. For other mounts,
the motor drives the worm shaft
using a set of spur gear reductions.
Polar Cone on Rocker Base
Right Ascension Worm Drive

Page 11
Equatorial Forks
An equatorial fork assembly consists of the two fork arms, a central hub, and
telescope mounting plates. One fork arm, usually on the east side of the mount,
houses the declination axis with worm gear drive and servomotor. The gear
casing that is attached to the outside of the fork arm contains this declination
drive assembly. It functions the same as the worm drive gear on the polar axis.
The second fork arm supports the declination axis on the other side of the mount.
A counterweight is typically located inside of the fork arm and on the outside
face of the arm. These weights balance the weight of the drive assembly on the
opposite fork arm. This balance is done at the factory and should require
minimal adjustment. To fine tune the fork arm balance, we provide auxillary
holes in the fork arms in which one can attach small auxillary weights.
Equatorial Fork Mount

Page 12
For mounts with Renishaw encoders, the second arm has a casing that contains
the declination encoder ring and the read-head assembly.
The two fork arms attach to the central hub, and the hub attaches to the top of the
right ascension axis. When attaching the fork arms to the hub or the hub to the
polar base, make sure that all surfaces are clean and free from dirt. These
surfaces are machined flat, and for proper arm alignment, it is important that
the components mate properly.
Telescope Plates
The telescope adapter plates connect the telescope to the fork arms. In general,
these plates are custom made for each customer, and in most cases are dovetail
plates or simple brackets.
The separation of the fork arms
is carefully calculated based on
the dimensions of the customer’s
optical tube assembly. However, we
allow a small amount of clearance
to facilitate sliding the optical tube
assembly into the fork arms. This
is typically .020 inches, .50mm
In the photo to the right, there is a
custom dovetail plate for a CDK 20
telescope.
Below to the right is a custom
mounting plate for an older Celestron
14 telescope.
PlaneWave Dovetail Plate
Brackets for a Vintage C14

Page 13
Altazimuth Fork Mounts
An equatorial fork mount uses celestial coordinates and moves along lines of
right ascension and declination in the sky. An altazimuth fork mount uses local
horizon coordinates, and moves along lines of azimuth and altitide in the sky.
One major advantage of altazimuth fork mounts is that they can support a
larger payload than an equatorial fork mount. The altazimuth fork assembly is
supported directly over the observatory pier. The fork arms are vertical, and
the azimuth base is horizontal. This simplifies the contruction of the mount,
facilitates installation, and produces an instrument with a minimum “footpint”

Page 14
Azimuth Base Assembly
Azimuth Base
The altazimuth fork mount has an
azimuth base assembly. The lower
base plate attaches to the top of the
observatory pier. Like the equato-
rial polar assembly, the azimuth
assembly features a gear casing,
which contains the worm gear drive
and servomotor. The azimuth axis
passes through the base, and it is
supported by two bearings with a
thrust nut on the bottom of the base.
Altazimuth Fork
The altazimuth fork
assembly is nearly identical to the equatorial fork. It consists of the two
fork arms, a central hub, and telescope mounting plates. The fork arms and
fork hub are attached to the top
surface of the azimuth axis.
A gear casing is attached to the
outside of one fork arm, and it
contains the altitude drive gear with
stainless steel worm and servomotor.
On the opposite arm, there is a
counterweight located inside the
arm and a smaller weight on the
outside face of the arm. The two
arms have approximately the same
weight, so that the fork assembly is
balanced.
For mounts with Renishaw encoders,
the opposite arm features a casing
that contains the altitude encoder
ring and the read-head assembly.
Altazimuth 750 Fork Mount

Page 15
Electronic Controls
Servo II
Each telescope mount includes a computer control system. The MI-500, MI-750,
and MI-1000 mounts are normally supplied with the Servo II computer control from
Sidereal Technology. This is the standard computer control package we use
with our mounts.
The Servo II control has a rich set of features including the following:
Can be used with a variety of servomotors including Pittman and Maxon
Uses high quality industrial Turck cabling and connectors
Provides continuous tracking and full “GoTo” capability
Supports adjustable drive rates for tracking any solar system object
Outputs 4 amps per axis at 24 volts
Uses separate cables for encoder signals and power lines to the motor
Features hardware sensors on the worm shaft for PEC correction
Supports homing sensors on each axis for remote operation
Offers secondary high resolution encoders for arc second tracking and pointing
ASCOM capatible for use with most PC software
The Servo II control supports German
mounts, equatoral fork mounts, and
altazimuth fork mounts. It has an open
architecture that gives access to nearly
every motor and control parameter.
Using Pittman 9000 or 14000 series
motors, the Servo II provides a motor
encoder resolution of about 0.10 arc
seconds per count.
The Servo 2 control includes industrial
quality cables, two for each axis of the mount. One cable provides power to
the servomotor. A separate cable is used for motor encoders, the PEC sen-
sor, and the home sensor. This feature isolates any electronic noise from the
servomotors and sensors.
Servo II Control

Page 16
The Servo II control features a PEC
(periodic error correction) sensor
on the RA worm shaft. This sensor
records the phase of the worm
rotation. Since the phase of the
worm is always known, a periodic
error profile can be applied to
the worm rotation, even after
powering down the controller.
The PEC does not depend on
timing the rotating worm. Rather,
the worm phase is determined by
the infrared sensor on the worm shaft.
The Servo II also supports mount homing. This feature enables telescope
control from a distant location. Homing disks are installed on the right
ascension and declination
axes. An infrared sensor on
the axes records the zero home
position. This home position allows
one to know the mount orientation
from any remote location. With
this information one initializes the
mount and then remotely controls
the telescope position
The Servo II control supports Renishaw high resolution encoders. These
encoders are attached to the axes of the mount. With a typical resolution of
.10 to .20 arc seconds, they precisely record all angular motion of the mount.
Independent of the drive gears and motors, Renishaw encoders measure the
position of the mount to an accuracy 10x greater than the gears alone.
Servo 2 Homing Sensor
Servo 2 PEC Sensor

Page 17
AstroPhysics GTO4 Control
AstroPhysics GTO4
The AstroPhysics GTO4 Control is a popular telescope control that offers many
advanced features. As an option, we offer this control for our M-500 and MI-750
mounts.
Using Swiss DC servo motors, this
drive system provides smooth track-
ing with motor encoder resolution of
0.10 arcseconds per encoder count. The
GTO4 has a speed range of 4800:1, which
provides 0.25x sidereal rate for guid-
ing and 1200x sidereal rate for slew-
ing. The GTO4 includes a very detailed
operation manual.
The GTO4 keypad is a hand-
held computer with the features and functions to control the tele-
scope. The GTO4 control can be used with a laptop or desktop com-
puter in conjunction with planetarium software. You can position the
telescope, center an image and control the tracking rate, set the reticle
brightness, and then park the telescope at the end of the night.
The GTO4 control requires a regulated 12-18 volt power supply with a mini-
mum output of 4 amps. This control can be used with our MI-500 and MI-750
equatorial fork mounts.
In comparison with smaller portable mounts, our family of MI mounts are large
and capable of carrying heavy tube assemblies. In using the GTO4 control,
we recommend that you set the maximum slew rate to 600x sidereal. If you
slew at a faster rate, the motors will not be damaged, but they will not slew
at the higher rate. The motors could possibily be overloaded, and this could
cause premature failure. Keep the maximum slew rate to 600x.

Page 18

Page 19
Polar Cone in Shipping Box
Fork Arms in Shipping Box
Installation
Un-crating the Mount
Most mounts are shipped by truck freight or by airfreight. Typically, a shipment
consists of between two and four containers.
We crate the mount components in heavy wooden boxes and secure the
parts using wood screws, nuts, and bolts. This ensures that there is no
shifting of the parts during transit. Over the past 10 years, we have
had essentially no damage to any mount component during shipment.
To disassemble the shipping boxes,
you will need a power drill and
Phillips head driver. Proceed slowly.
First remove the top of the box. and
then remove the sides. Some large
components are bolted to the bottom
of the box, or others are attached to
wooden platforms. It may take an
hour or more to uncrate the mount.
Hardware
Each mount is shipped with
the necessary tools and hardware.
We include a set of English/Ameri-
can hex wrenches and other special
tools that you will need to assemble
the mount components.
Base Plate and Pier
The first step in installing the mount
is to attach the base plate to the
observatory pier. It is important
that the plate be firmly attached,
since the weight of the mount and
telescope is supported by the base
plate on the pier. In most cases,
custom holes have been machined in
to the base plate and these should
match the top holes in the pier.

Page 20
Rocker Base on Base Plate
Polar Cone on the the Rocker Base
Rocker Base
After the base plate is bolted on the pier, the rocker base is bolted to the base
plate. Before placing the rocker base on the base plate, apply a small amount
of grease on the mating surfaces. This will permit the rocker base to slide
easily on the base plate, facilitating
making changes in the azimuth
angle of the polar assembly.
A shoulder bolt passes through the
hole in the center of the rocker base
and screws into the center hole in the
base plate. This center bolt serves
as a pivot pin to keep the polar
assembly centered on the base plate
when changing the azimuth angle
of the mount.
Bolt the rocker base to the base plate
using five stainless steel hex head
bolts. These bolts pass through the
slotted holes along the edge of the
rocker base.
The polar cone and rocker are then
placed on top of the rocker base.
Apply a small amount of grease to
the mating convex-concave surfaces.
Bolt the rocker to the rocker base
using four stainless steel hex head
bolts. These bolts pass through the
slotted holes along the edge of the rocker.
Fork Hub
In most cases, it is best to first attach the fork hub to the polar axis, and then
attach the fork arms to the hub. With the polar (or azimuth) assembly in place,
attach the fork hub to the top of the polar (or azimuth) axis. First thread the
1/2 inch guide pin in to the center of the polar axis This 1/2 inch threaded pin
is for alignment and to temporarily support the fork hub in place. The fork hub
is not secure until it is attached to the polar axis with all the provided hardware .