Mounts: 900GTO

ASTRO-PHYSICS HISTORY
900GTO German Equatorial Mount (900GTO)
with GTOCP2 Control Box
Includes Go-to Keypad Controller and DigitalSky Voice™ software

The 900GTO German Equatorial Mount with the GTOCP2 Control Box is not available to purchase. This information is provided for present owners and those who are curious about its history. It is based on original information with some updates. If you are interested in some of the other models, check out this Brief History of the 900 German Equatorial.

Additional photo to view:

900GTO with 155mm f7 StarFire EDF(4" focuser model), 15" Ribbed Plate, 80mm Guidescope and other accessories

Stability ... accuracy ... ease of setup ... friendly go-to control interface - these were the primary design goals of the 900GTO. Amateurs today demand a precise mount that will allow them to pursue all aspects of astronomy whether it be observing visually, CCD imaging or photographing with 35mm or 6x7 camera. Many of the finest imagers today have been using our GTO mounts as a solid platform for a wide variety of instruments. If your instrument of choice is a medium-sized refractor, Cassegrain, Ritchey-Chretien, Newtonian or astrograph, we invite you to read on.

Since its introduction in 1998, the 900GTO has gained a reputation for both tracking and pointing accuracy, essential to casual visual observation as well as advanced imaging. Quite a few 900GTO and 1200GTO mounts can be found at Mount Pinos in California, favorite observing site of many advanced photographers and imagers.

These mounts are truly a marvel of engineering - maximum strength and rigidity with minimum weight. Our CNC lathes and mills carve out the excess material in both axes of the 900GTO German Equatorial while retaining a heavily ribbed structure for internal strength and rigidity. A unique dovetail was machined into the mating surfaces of the R.A. and Dec axes. This feature allows quick and easy assembly in the field without any tools.

The 900 equatorial is equally at home in a permanent observatory or as a portable mounting for remote star parties thanks to the ease with which the two axes come apart and the reasonable weight of each component; the heaviest is only 25 lbs! Telescopes commonly used include Astro-Physics 155-180mm refractors, 10-11" Schmidt-Cassegrains, 10" Maksutov-Cassegrains and 10-12.5" Ritchey-Chretiens and other scopes of similar size and weight.

The 900GTO mount is built from the ground up to be a precision imaging platform while still being totally user friendly. Consider these advantages and features:

Flexibility

Portable.
Extremely solid, rugged, high payload mount, yet comes apart in two reasonably light-weight components for hassle-free field setup. No tools needed to assemble the mount in the field.
Operate with 12V battery.
You can take it to the darkest skies and power it with a commonly available 12V battery. In the observatory, we suggest a minimum 5 amp filtered, regulated power supply.
External computer not needed.
The keypad is a handheld computer with all of the features, functions and databases you need to tour the universe night after night. The unique software allows you to precisely polar align your mount in the field, even in broad daylight! The vacuum-fluorescent display with a temperature range of -40 degrees F (and C, they are the same in this instance), allows hardy observers to use this mount on cold winter nights. You can't do that with a PC or PDA device!
Separate computer control.
All functions of the servo drive can be commanded from a laptop or desktop computer using popular planetarium software. Depending on the features of the program, you can position your telescope, center your image and control tracking rate, remote focusing, reticle brightness and park at the end of your observing session. Examples of currently available software:
- Software Bisque's suite which includes TheSky Astronomy Software, CCDSoft CCD Astronomy Software, TPoint Telescope Pointing Analysis Software and Orchestrate Scripting Software.
- Earth Centered Universe (ECU) by David Lane of Nova Astronomics
- SkyMap Pro 6 by Chris Marriot
- DigitalSky Voice by Charles Sinsofsky (included with the 900GTO)

Write your own computer program.
The Astro-Physics GTO protocol for the GTOCP2 Control Box is freely available to those who would like to write their own computer program for controlling the mount. While based on the Meade protocol, it has many more features and enhanced precision level which allows pointing and tracking to the 1 arc second level.

Precise Mechanical Fabrication

Highly accurate mechanics
Using modern CNC machining techniques, we make all components to a high precision level which results in a final package that is solid and accurate in all respects. The critical angles are accurately machined so that the mount is orthogonal to a very high degree. This results in pointing accuracies well below 1 arc minute for a properly aligned mount.
Worm gear accuracy
Critical worm gear accuracy is maintained by special machining techniques developed at Astro-Physics after extensive studies and actual field operation. Our worm accuracies are second to none. With good alignment, PEM training with the Keypad or by using PEMPro software, it is quite practical now to achieve unguided CCD images with today's hi-resolution cameras coupled to a 6" to 12" telescope.

Mechanical Features

All machined mounting made from aluminum barstock and stainless steel. All fasteners are stainless steel.
Motors and all electronic components are enclosed
Ball bearing races.
Removable 1.875" diameter counterweight shaft.
Polar and declination axes come apart quickly without tools for light-weight, easy handling and ease of transport
Fine altitude and azimuth adjustments for quickly and accurately zeroing in on the pole in the field
Engraved setting circles are Porter Slip Ring Design
Electronic components rated for industrial and automotive applications
Base fits into 8" outside diameter pier with 0.125" wall thickness

Specifications of Equatorial Head

R.A. worm wheel	7.2" (18.3cm), 225 tooth aluminum
Declination worm wheel	6" (15.2cm), 225 tooth aluminum
Worm gears	Brass
R.A. thrust surface	7.0" (17.8cm)diameter
Declination thrust surface	6.0" (15.2cm) diameter
R.A. shaft	2.2" (5.6cm) diameter
Declination shaft	1.75" (4.4cm) diameter
Latitude range	20 to 68 degrees 0 to 20 degrees with latitude wedge Azimuth adjustment
Azimuth adjustment	Approximately 14 degrees
Setting circles	Porter Slip Ring design, engraved
Right ascension	4 minute increments, pointer, engraved both Northern/Southern
Declination	1 degree increments, pointer
Capacity	Approximately 70 lbs. (31.8kg) scope and accessories, depending on length. Will accommodate Astro-Physics and similar refractors up to 180mm f9, 12" Cassegrains, 12-14" Ritchey-Chretiens Some telescopes are very heavy for their size and will require a larger mount.
Weight of equatorial head	50 lbs (22.2kg), Declination axis is 15 lbs. (6.8kg) right ascension axis is 25 lbs.(11.4kg), counterweight shaft is 10 lbs. (4.6kg)

Servo Motor Drive

The drive system uses a high-quality Swiss DC servo motor controlled by a microprocessor to an accuracy of 0.05 arc-seconds per step. Tracking is very smooth, noticeably smoother than any stepper motor drive or inexpensive servo motor. The system can be accurately controlled over a speed range of 4800:1 which allows 0.25x sidereal for guiding to 1200x sidereal for 5 degree per second slewing. The circuit draws only 0.4 amps when tracking the stars, 2 amps with both motors slewing and requires only 12 volts to operate. The servo drive will satisfy the requirements of the sophisticated, advanced astrophotographer, yet is easy for the casual, visual observer to use.

Dimensions

The diagram shows several dimensions that are commonly requested. In addition, if the scope is horizontal and pointing west or south, the measurement from the top of the pier to the middle of the cradle plate is 11.25." Please note that these dimensions will vary somewhat depending on your latitude. We quote them for 42 degrees because that is the latitude of Astro-Physics and all of our equipment is set up that way. It is also a good average value.

Support

We have prepared some pertinent support documents relating to this mount and many of our other products on our Technical Support page. Please check there first to find the information that you need.

Upgrades and Spare Parts

Check out our Astro-Physics.com website to find accessories, replacement parts or learn about possible upgrades for your mount.

Astro-Physics, Inc.
11250 Forest Hills Road, Machesney Park, IL 61115, U.S.A.
Phone: 815-282-1513 Fax: 815-282-9847