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Why an 1150GTO?

The 1150GTO is our new mid-sized observatory-class mount that delivers reliable operation in your automated imaging, remote observatory, or ready to travel to star parties where your 12V battery will keep it running all night.

We offer three versions: 1150GTO, 1150GTO-AE and 1150GTO-AEL. The latter two versions include the Standard Temperature Absolute Encoders or the Extended Temperature Absolute Encoders, respectively. If you order the 1150GTO without the absolute encoders, you will be able to purchase them as an upgrade at a later date to install yourself. 

New Features of the 1150GTO (*AE/AEL Denotes Features of 1150GTO-AE and 1150GTO-AEL)

• Increased instrument capacity - 125lb/ 57KG
• Fully integrated through-the-mount cabling, including power, USB, and Ethernet; RA and Dec axes can still be separated
• Quiet, powerful belt drive
• Self-synchronizing PEM means PE curve never loses phasing
• High frequency PE eliminated for smoother tracking
• Flexible 12-24V DC power
• AE/AEL. Sky-Aware Axes - loosen the clutches to move and it will still know its pointing position (similar to Mach2)
• AE/AEL. Enhanced tracking precision - PE 0.19 with Absolute Encoders

Additional Features (*AE/AEL Denotes Features of 1150GTO-AE and 1150GTO-AEL)

• Polar Align, Power Up and Go!
• Precision balancing via the clutches without taking the worm gears out of mesh
• Brushless Micro-step motors for precise and whisper-quiet slewing and tracking
• Dual-model pointing and tracking rate correction even with the telescope in the counterweight UP position. using Astro-Physics Command Center (APCC) Pro version, included
• Custom tracking rates in both axes (for NEO targets including asteroids, comets, satellites)
• Auto-Adjusting gear mesh
• Image all night without meridian flip, as long as your scope clears pier/tripod
• Daytime polar alignment is simplified with defined park positions
• Precision azimuth adjuster with rotating base
• Built-in bubble level
• Fully-supported enhanced ASCOM V2 driver 
• Portable – Axes can be separated for easy transportation/setup
• Right-angle polar alignment scope (optional) 
• Threaded for QHY Polemaster
• Flexible power options: Operate with 12V battery or up to 24V DC power supply
• AE/AEL Renishaw Absolute Encoder for the ultimate in precise tracking - no SDE or random errors above 1/4 arc sec. Extended Temperature option available. 
• AE/AEL Absolute encoder provides near zero tracking error and resists outside influences such as wind and cable drag
• **   AP Quality   **   AP Reliability      AP Support   

GTOCP6 Control System

Gear Accuracy and PE Performance

Each mount is rigorously tested with our specialized software to meet or exceed our periodic error specifications of 7 arc seconds (+/- 3.5 arc sec.) before introducing any periodic error correction. Only mounts that provide an accuracy of 7 arc seconds or better will pass this inspection. We also evaluate other characteristics of the PE curve to ensure smooth tracking and guiding. If the mount exhibits greater error, the substandard part is identified, replaced and the mount retested. 

Pre-loaded Optimized PE Curve

In order to optimize performance even further, we generate a unique PE curve for each mount that is programmed into each GTOCP6 control box. Simply use your Astro-Physics software (ASCOM V2 driver or APCC) or optional KEYPAD (KEYVFK2) to turn the PE correction "on". You will see results that are significantly better than our published 7 arc second spec without additional PEMPro runs! However, we provide PE so that you can touch-up your PE curve as needed over the years. 

1150GTO-AE and 1150GTO-AEL: If you purchase either of these versions that feature absolute encoders, the absolute encoders provide continual corrections throughout your observing session. They do not rely on the stored curve. 

Features of the GTOCP6 

• The GTOCP6 is designed exclusively for the unique drive system of the 1150GTO (with or without encoders). It cannot be used with any other mount. 
• Direct download of future firmware updates from the Software Update tab of our website (very quick and easy). 
• Both axes can be run at custom tracking rates from sub-arc second motions per hour to 1000x sidereal.
• GTOCP6 brushless micro-stepper motors can be run from 24 volts to 12 volts with max slewing to 1200X (5 deg/sec).
• Power to the motors is self-limiting and cannot cause any kind of damage to the windings or the electronics, even when in a stalled state.
• Offers multiple connection options to suit your requirements including Wi-Fi, Ethernet, USB and serial port. 
• Applies safety slew logic to all slew commands regardless of source. This ensures that your mount will slew safely from a counterweight up position or into a counterweight up position while using the meridian delay feature.
• Each GTOCP6 is matched to the mount and will bear the same serial number. The initial firmware download includes the unique characteristics of that mount. It cannot be swapped with another 1150GTO. 
• AE/AEL   Use of Absolute Encoders means that the mount always knows where the axes are pointing and doesn't need to establish home on power-up.
• AE/AEL   Absolute Encoders are extremely accurate in slewing, pointing, tracking, guiding. Periodic error and backlash, reversal delays in Dec are eliminated.
• AE/AEL   Rapid encoder loop stiffens the axes against outside disturbances such as cable drag and wind loading.

GTO Keypad (optional accessory)

The Keypad is a self-contained computer that allows you to control all essential telescope functions and includes an extensive database of objects. The new V5 version includes modeling routines for pointing, tracking and orthogonality.  Many people do not want to bother with a computer in the field and like the handiness of the Keypad and its ability to operate in very cold temperatures. The Keypad is an ideal choice for these users.

We have designed the interface and firmware to be as intuitive and easy to use as possible, while filling it with terrific features to make your observing session productive and pleasurable.

Optimized for Astronomy

Astro-Physics mounts and the Astro-Physics GTO Servo Control System are designed from the outset as tools for celestial observing and imaging.  These mounts do not have any military or defense applications. Applications like missile, airplane, or very low earth orbit satellite tracking require faster tracking rates and more rapid changes to those tracking rates than our mounts allow.   Note that the ISS is generally within the mount’s tracking rate capabilities. 

1150GTO and Renishaw Absolute Encoders Option

1150GTO Enhanced Tracking Performance with Absolute Encoders - PE = 0.19 arc seconds

Two versions of the mount are available with Renishaw Absolute Encoders installed: 1100GTO-AE (standard) and 1100GTO-AEL (extended temperature). If you decide that absolute encoders would enhance your astro-imaging and remote control of your mount, we encourage you to purchase the mount with the encoders installed and tested during assembly of your mount. We plan to offer them in an upgrade kit at a later date, however the installation process is more complicated than our previous 1100GTO or the 1600GTO mounts due to internal wiring. 

Benefits of Absolute Encoders

The utility of absolute encoders varies from one mount brand to another.  Some manufacturers make very limited use of encoders and use relative (not absolute) encoders to provide a potential benefit to tracking and nothing else.  In regards to the 1150GTO, the benefits of absolute encoders are:

• Sky-Aware Axes - The mount always knows where it is pointed regardless of power loss, movement of the axes when the power is off, bumping the mount or wind movement. 
• No rehoming is required for remote locations should there be a power loss.
• Periodic error is fully corrected. No need for occasional PE measurement curves.
• Zero backlash in both axes for precision guiding.
• Dual-axis absolute encoders allow for variable tracking that automatically adjusts for refraction parameters.
• Very accurate pointing makes it easy to find very faint objects.
• Very precise tracking such that unguided imaging may be accomplished with an appropriate optical/imaging setup.
• Very precise guiding, if needed, with instant response in both axes.  Guiding is only needed to correct for optical/imaging train issues, not mount issues.
• Corrects for polar misalignment and repeatable mechanical flexure.
• Very precise dual-axis tracking is very important for high precision tracking on objects like comets, asteroids, artificial satellites, where the mounts use a "self-guiding" function based on orbital elements.

We invite you to review the additional technical information regarding the encoders to find out what they can do for you.  

What are the main differences between the Renishaw Absolute Encoders and other less expensive relative encoders used on other mounts?

Lab Certified Accuracy! 
The Renishaw encoder accuracy is verified against a laboratory standard. Each ring comes certified with its own calibration measurement. The maximum guaranteed error on these rings translates to less than 1/2 arc second per hour tracking error.

Highest Resolution for Unparalleled Tracking Accuracy!
The Renishaw Resolute read-head interpolates a special barcode that is engraved on the matching stainless steel ring into 67 million individual addresses. Every address is unique and fully reproducible down to sub-arc second levels. This is not possible with any relative encoder system.

Ripple and Resonances – NOT with Astro-Physics!! 
The Renishaw absolute encoders do not have the following disadvantages present in relative encoders. Relative encoders use a simple ring that has engraved marks with separations on the order of 60 to 100 arc seconds between ticks. In order to achieve sub-arc second resolution, the gaps between these marks are filled in electronically by a method known as interpolation. Even the best interpolation methods have errors on the order of 5% (3 to 5 arc seconds). When used in a telescope drive system these relative encoders introduce a fast moving ripple in the RA tracking rate of 3 to 5 arc seconds, although the average or RMS value of this error can be quite low.

These peak excursions cause stars to move slightly back and forth in the RA direction during sidereal tracking. This tracking ripple can remain hidden when imaging with short wide-field scopes, but will manifest itself when using long focus instruments for high resolution work. It is generally a fast moving error, so it cannot be guided out.

No Sub-divisional Error! 
Because of the ever present interpolation error (SDE) with low-cost relative encoders, we decided long ago that we would not use them for tracking. Renishaw absolute encoders use a different type of interpolation system that smooths out the SDE to a level that is not detectable. There is no mechanism for a relative encoder to remove the SDE.

Never Needs Homing. Simply Polar Align; Power Up; and GO!! 
An absolute encoder mount never needs to be homed. It is always home the minute power is applied. It always knows where it is and transmits the exact shaft position to the control box at all times.

Dependability to Astro-Physics Standards!
We have used Renishaw encoders for many years on our larger mounts, both in portable setups and in observatory remote installations. They have been totally reliable. Renishaw encoders are also considered to be the gold standard in the machine tool and robotics industries where precision is required. Yes, they are much more expensive than a simple relative encoder, but for the type of accuracy required in a telescope mount, there is nothing out there that comes close. We know, we have been evaluating options for years.

Mechanical Specifications

GTO Drive Specifications

Flexible Control with Your Keypad, Computer or even your Mobile Smart Device!

As this chart shows, there are many options available for controlling your mount. Take a few minutes to link to descriptions of the varied software and devices that are available.  You will be able to link to a full-sized view of this chart.

Control Options for Astro-Physics Mounts

Astro-Physics control boxes support a wide range of connectivity. Physical connectivity includes RS232, USB, ethernet and WiFi. The included state-of-the-art ASCOM driver supports connectivity with all ASCOM-compliant software, including NINA, Sequence Generator Pro, Maxim DL, TheSky, Voyager, and many others. The Indi driver enables connectivity to KStars, Ekos, ASIAir, and other Indi-specific apps (Indi driver is developed and supported by third party) 

1150GTO German Equatorial Mount

• 1150GTO Equatorial Head
• 1150GTO-AE or 1150GTO-AEL have Dual Absolute Encoders factory installed
• GTO Servo Control Box (GTOCP6)
• Control Box Adapter (M11010KIT)
• 16.5" (42 cm) Stainless Steel Counterweight Shaft, 1.875" (47 mm) diameter with Machined Safety Stop Knob (M12676)
• Power Cable Set with Powerpole Connectors (CABPP4SET)
• Allenhead wrench set
• ASCOM driver, available by download
• APCC Software, Pro version (APCC-PRO) license included
• Thumb Drive containing: PEMPro v3 software written by Ray Gralak of Sirius Imaging. Also, PDFs of manuals and other handy utilities.
• Manuals: 1150GTO German Equatorial and GTOCP6
• Registration Card
• Power supply NOT included, must be purchased separately

Items You will Need for Your Mount

• 12-24V DC power supply: PSBPW25A, PS24V6APP-A-SET, PS141V30A
• Counterweights: Stainless Steel Counterweights - 5, 10, 18 lb.  (5SCWT, 10SCWT, 18SCWT, 30SCWT188) (due to larger diameter 30SCWT188 is not recommended for use at top of the shaft)
• Mounting Plates: DOVEDV10 or DOVELM162
• Refer to USB 3.0 Internal Cable Considerations below to plan your cable requirements.

Support Pier and Tripod Options

Minimum 8" diameter recommended

Permanent Piers

• Advanced Telescope Systems ATS 8" permanent pier
• requires 119FSA-FP flat surface adapter
• SkyShed 8" permanent pier
• requires 119FSA flat surface adapter
• Build your own concrete pier using the 119FSA flat plate adapter and adapter from Dan's Pier Plates

Always contact third party vendors to confirm configuration, pricing, and availability.

Portable Piers and Tripods

• Astro-Physics Portable Pier - 8" diameter, available heights 32",42",48"
• Advanced Telescope Systems (ATS) 8" Portable Pier
• requires 119FSA-FP flat surface adapter
• Losmandy HD Tripod
• requires 119FSA flat surface adapter

Always contact third party vendors to confirm configuration, pricing, and availability. 

Additional Accessories to Consider

• GTO Keypad with 15' Coiled Cable and Keypad Protector (KEYVFK2)
• Right-Angle Polar Alignment Scope with Illuminator (RAPAS), requires attachment Bracket (RAP1150)
• Pier Accessory Trays (TRAY06 and TRAY06H) and Support Bars (TRAYSB1 and TRAYSB)
• Extension to allow 1150 or 1100 Control Box Adapter to be used with 10" pier (Q6281KIT)
• Side-by-Side Dovetail Plates for D-Style Dovetail Saddles (SBD13SS, SBD18SS)
• 13.7" (35cm) x 1.875" (47mm) Counterweight shaft (M2043) to use with smaller, lighter scopes.
• 9.25" (23cm) x 1.875" (47mm) Counterweight Shaft Extension (M12675)
• 22" (56cm) x 1.875" (47mm) Counterweight Shaft (M12601-E) for heavier loads rather than adding a shaft extension. 
• Alligator Clips with APC Fuse to Powerpole Connector (CABPPAL)
• Powerwerx In-line Watt Meter shows volts, amps, watts, amp-hours, watt-hours. (CABPPWM)

USB 3.0 Internal Cable Considerations

As mentioned, the mount includes an internal USB 3.0 cable for your convenience. It is important to remember that passive USB 3.0 cables (including the ~2 foot internal cable) can be no more than 9 feet (3 meters) in total length from a powered port and passive USB 2.0 cables can be no more than 15 feet (5 meters) in length from a powered port. With that in mind, you will need to plan your computer cabling carefully. With USB, shorter is better.  These are our current recommendations:

Connecting Computer to Mount Internal Input
These connections are made to the 1150GTO Back Plate on the RA axis.

Using USB 3.0 Active Cable and Short USB Cable

• USB 3.0 Active Cable (male A-to-female A).  Example: Tripp Lite USB 3.0 Active Extension Repeater Cable (USB-A M/F) 
• USB 3.0 male A-to-male A Cable for Data Transfer (short cable).  Example: UGREEN USB 3.0 Type A Male-to-Type A Male Cable for Data Transfer, 1.5-ft

Connecting Mount Internal Output to Communication/Power Hubs
These connections are made to the Dec axis Top Plate just under your mounting plate.

Using Pegasus Astro Ultimate Powerbox and Pocket Powerbox Advance

• USB 3.0 male A-to-male B Cable (standard)
• Custom 12 volt Cables with Anderson Powerpole Connector to XT-60 Female Connector (Ultimate Powerbox) or RCA Male Connector (Powerbox Advance).  It is recommended to use a 16 to 18 AWG cable. 

Using USB 3.0 Communication Hub and RIGRunner Power Distribution

• USB 3.0 male A-to-male B Cable (standard)
• USB 3.0 Powered Hub.  Example: Gearmo USB 3.0 4-Port Industrial Metal Hub w/15KV ESD Protection
• Powerwerx Power Distribution
• Custom 12 volt Cables with Anderson Powerpole Connectors
• 4 Position Power Distribution Block for 15/30/45A Powerpole Connectors
• West Mountain Radio RIGrunner 4005
• Cat6A Ethernet cable - standard Cat6A cable

Using Primaluce Lab Eagle Communication Hub and Power Distribution

• USB 3.0 male A-to-male B Cable (standard)
• Primaluce 12 volt Power Cable to Anderson Powerpole Connector

Availability

The 1150GTO is in production for delivery beginning late August 2025.