Astro-Physics 3600GTO German Equatorial Mount with Precision Encoders
Astro-Physics 3600GTO German Equatorial Mount
"I am in the process of planning a trip to the remote observatory I own at Arizona Sky Village. I realized that the last time I was there was to install the AP3600GTO in April of last year and that since that time it has been operating every clear night and has not missed a beat ...The mount has been running for over one year and surpassed my expectations in every way". - David Churchill ". . . I love the ability to place the OTA on the "wrong side" of the mount when starting an imaging session ("premature meridian flip") and which I have used extensively. This feature is pure INGENUITY!" - Anthony Ayiomamitis Image Past the Meridian
The AP 3600GTO mount will track and guide well past the meridian in either direction if the object is located such that the telescope will clear the pier. This allows the user to set up the 3600 mount for a long series of exposures without stopping in the middle to flip sides. One can start the telescope under the mount while pointing at an object in the eastern part of the sky and track it all the way deep into the western sky. This is very useful for long exposure H-alpha or in cases where a large number of individual exposures are needed for stacking. Full 360-degree Rotation of Both Axes
The full 360-degree rotation of both of the 3600GTO's axes also allows this mounting to be placed onto an astrographic pier for complete freedom from movement restrictions. Contact OPT to discuss astrographic piers.Through-the-Mount Cabling Capability
Astro-Physics designed this mount to allow cabling to be run through the axis shafts for tangle and clutter-free operation. Cables from cameras, guiders, dew heaters and the mount's own servo drive can all be run through the AP 3600 mount's cavernous 4" hollow shafts, where they are out of the way and where they won't ever get caught or tangled during your imaging session. Ports have been included for the mount's servo cables. Additional ports can be added by the user, as needed. Components are Modular and Easy to Maintain
The design of the Astro-Physics 3600GTO mount is straightforward, with modular construction and no complicated internal wiring. All electronics including the GTOCP3 control box, motors, gearbox or cables can be removed for servicing. The RA and Dec axes can be shipped separately, if needed. The mechanical design of the 3600 mount is extremely simple and effortless, allowing easy adjustment by anyone - no need to have a mechanical engineering degree to service the mount. Integrated Pier Adapter
The pier adapter for the 3600GTO mount has been integrated into the mount's design and incorporates the design principles of the Precision Adjust Rotating Pier Adapters available for smaller Astro-Physics mounts. In an innovative twist, the Super Heavy-Duty Azimuth Adjuster is UNDER the BACK of the mount where it is conveniently located for fine polar alignment and remains out of the way. Polar alignment is smooth and easy, and the system locks down tight with no unintended movement. Easy to Adjust and Polar Align
Precise polar alignment can be achieved easily using the precision adjusters on the 3600GTO mount for both altitude and azimuth. The system locks down with zero alignment shift for an unprecedented ability to achieve that "perfect dead-on" polar alignment that is so critical to the best imaging and the most accurate go-to slews. The PEMPRo Software program (included with the mount) includes the "Polar Alignment Wizard," a powerful feature that allows you to dial in on the pole quickly. Transportable
The Astro-Physics 3600GTO is an extremely solid, rugged, high-payload mount, yet the equatorial head comes apart in two components for transport and field setup. Because of this mount's size and weight, we recommend that field assembly be done by at least two people working together. The RA axis/base assembly alone weighs just over 120 lb. You wouldn't want to transport it as your regular mode of operation, but it can certainly be done for special occasions. Precise Mechanical Fabrication
Using modern CNC machining techniques, AP makes 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. The machinists at Astro-Physics are among the most skilled available anywhere, attending to the smallest detail to ensure a precision instrument. The finishing department assures that all parts are de-burred, sanded, polished and painted to provide an exceptional aesthetic appearance. Mount assembly is directed by a life-long astronomer with more than 20 years of experience at Astro-Physics! All of their production personnel take great pride in their work and are true craftsmen and women. Worm Gear Accuracy
Critical worm gear accuracy is maintained by special machining techniques developed at Astro-Physics after extensive studies, actual field operation and many years of experience making precision mounts. Their worm accuracies are second to none and are guaranteed to be 5 arc seconds (+-2.5 arc sec.) or less, peak-to-peak. The periodic error of each mount is verified during intensive testing procedures. Pre-Programmed with PEMPro
Periodic error corrections for each individual mount are optimized during extensive testing, which results in excellent performance right out of the box. The spec of 5 arc seconds (+/- 2.5 arc sec.) is the maximum native mechanical error inherent in the mount's RA axis WITHOUT any software correction. AP optimizea performance further by characterizing the error using a special version of PEMProAP and downloading the appropriate correction into the mount's GTOCP3 before it leaves Astro-Physics. Simply use the Keypad or PulseGuide software to turn PE Correction "on," and you will see results that are even better than the published 5 arc second spec! With additional PEMPro runs, you can achieve even higher levels of accuracy.
Mechanical Specifications for the AP 3600GTO Mount
- Construction: All CNC machined aluminum bar stock, stainless steel, brass; stainless steel fasteners
- Finishing and Assembly: Every part is hand-finished and inspected. All assembly is done by hand, by highly skilled mount assembly staff.
- Worm wheel - R.A./Dec: 13.0" (330 mm), 256 tooth aluminum
- Worm gear - R.A./Dec: Brass, 1.41" (35.8 mm) diameter
- Axis shaft - R.A./Dec: 4.72" (120 mm) diameter with 4.02" (102 mm) clear inside diameter
- Shaft axis bearings - R.A./Dec: 7.09" (180 mm) diameter deep groove ball bearings
- Worm gear bearings: 1.57" (40 mm) angular contact ball bearings
- Latitude range: 15-70 degrees
- Azimuth adjustment: Approximately 14 degrees (+/- 7 degrees from center)
- Counterweight shaft: 2.5" (64 mm) diameter x 31.5" (800 mm) long [30" (760 mm) useable length], incl. large machined safety stop knob. Will fit 12 optional 30 lb. (13.6 kg) counterweights. Optional 10" (254 mm) shaft extension available.
- Weight of mount: Total: 247 lb. (112.3 kg); R.A. axis/polar fork: 121 lb. (55 kg), Dec. axis: 84 lb. (38.2 kg), Counterweight shaft: 42 lb. (19.1 kg)
- Capacity: Conservatively rated for 300 lb. (136.4 kg) scope and accessories (not including counterweights). Recommended for: 20" and 24" Ritchey-Chretiens and CDKs.
- Instrument mounting interface: Declination hub has ten 3/8-16 tapped holes on a 12.000" bolt circle.
- Diameter of base: 11.480" (291.6 mm) diameter. Use of the Flat Surface Adapter (3600FSA) is highly recommended.
GTO Servo Drive System Specifications
Servo Motor Drive
- Electronic components: Rated for industrial and automotive applications
- Motors: High-torque, zero-cogging Swiss DC servo motors, enclosed in machined aluminum housing
- Motor encoder: 2000 tic quadrature yielding an effective resolution of 0.044 arcseconds per tic
- Motor reduction gear train: 57.6:1 gear reduction through a custom built set of large diameter, fine-toothed, precision, spur gears for vastly superior performance
- Servo Motor Control Box: GTOCP3 Control Box, removable
- Hand-held computer: GTO Keypad to control all mount functions. Includes extensive databases and tour features in a simple, intuitive interface. Firmware updates via the internet
- Power consumption: ~ 0.4 to 0.8 amps at 15 volts - tracking ~ 1.5 to 3.0 amps at 15 volts - both motors slewing at top speed of 600x
- Power requirements: Nominal 15 volt DC supply at 10 amps recommended
- Periodic error: 5 arc seconds peak-to-peak (+/- 2.5 arc seconds) or less in one worm cycle (5.6 minutes); native, prior to any error correction
- Maximum slew speed: 2.5 degrees / second
The drive system for the AP 3600GTO mount uses a high-torque precision Swiss DC servo motor in each axis controlled by a microprocessor in the GTOCP3 control box. The encoders on these motors provide a resolution of 0.05 arc seconds per step for incredible pointing accuracy. Tracking is very smooth, noticeably smoother than any stepper motor drive or inexpensive servo drive. The system can be accurately controlled over a speed range of 4800:1 which allows 0.25x sidereal for manual guiding to roughly 720x sidereal for 3 degrees per second maximum slew rate. The circuit draws well under an amp when tracking the stars, 3 to 5 amps with both axes slewing and requires only 12 volts to operate (15-18 volts is recommended). This servo drive will satisfy the requirements of the sophisticated, advanced astrophotographer, yet is easy for the casual, visual observer to use. The GTOCP3 Control Box contains all of the circuitry to drive the servo motors and the logic required to navigate the sky. It can be easily removed from the mount, if required. The GTO Keypad is a self-contained computer that serves as the communication center for the operation of your GTO mount. 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. For reliable operation in your observatory, Astro-Physics recommends that you use a minimum 10 amp filtered, regulated power supply like the AP 15V, 10-amp power supply (PS15V10AC). For lighter, well-balanced loads, you can use a commonly available heavy-duty, deep-cycle marine 12V battery. Flexible Control with Either Keypad or Personal Computer Keypad Operation
The keypad is a handheld computer with all of the features, functions and databases you need to tour the universe night after night. The vacuum-fluorescent display with a temperature range down to -40 degrees F (and C, they are the same in this instance), allows hardy observers to use the keypad on cold winter nights. As new firmware versions are released in the future, you can upgrade your keypad directly from the download section of the AP website, free of charge.Remote Control with personal computer, if desired
All functions of the servo drive can be commanded from a laptop or desktop computer. Astro-Physics now has a wholly-owned and fully-supported ASCOM V2 driver for all of their GTO mounts. This is now the recommended method for mount control with a personal computer operating under the Windows operating system. Most popular Windows planetarium, imaging, guiding and observatory control software take advantage of ASCOM’s universal applicability. The Astro-Physics V2 ASCOM driver also acts as a hub allowing multiple client applications to connect to a single serial port without the need for POTH. The GTOCP3 control box provides two RS-232 inputs so that you can connect with two separate serial interfaces. This allows Mac users and non-ASCOM programs to have more than a single connection to the mount. For example, you might wish to connect PulseGuide as well as an ASCOM client at the same time with your Windows computer. On the Mac side, you might wish to connect both Astro-Planner and Equinox for an observing or imaging session. Please note that AP cannot fully support Mac programs at this time.PulseGuide’s Software
PulseGuide is a stand-alone Windows (98, ME, 2000, NT4, XP, Vista and Windows 7) utility that provides complete remote control of Astro-Physics Mach1GTO, 400GTO, 600EGTO, 900GTO, 1200GTO, 1600GTO and 3600GTO mounts. It derives its name from its most distinctive feature, pulse guiding, which can improve unguided tracking. Specifically, it can help correct tracking errors caused by polar misalignment and atmospheric refraction. You can also train PulseGuide to track objects moving relative to the stars, such as asteroids, comets, and the moon. In addition to pulse guiding, PulseGuide also has many useful utility features. With just a few exceptions, it supports the entire serial Astro-Physics command protocol.PEMPro v. 2.0 Software - FULL Version!
PEMPro (Periodic Error Management Professional) is a Windows software application developed by Ray Gralak that makes it easy to characterize and reduce periodic error. While the periodic error of your 3600GTO has already been optimized with a special version of PEMProAP to be well under 5 arc seconds (+-2.5 arc sec.) or less, you can reduce it even further to maximize performance without auto-guiding. PEMPro v. 2.0 is the latest version of PEMPro and includes exciting new features like the "Polar Alignment Wizard" to quickly, accurately and easily dial in your polar alignment. The software will be included with all new 3600GTO mounts.
Precision Encoder System on the 3600GTOPE Mount
A precision encoder installed in the RA axis provides feedback to the servo to eliminate periodic error to a level below 1/2 arc second for long-period exposures. This feedback system eliminates periodic error by monitoring the actual output speed of the RA axis using this encoder ring to continuously adjust the speed of the servo motor, which keeps the axis rotating at a very precise and constant rate. The operation of the encoder does not interfere with any external guiding, centering or slewing commands sent by the keypad, CCD camera or external software. Its only function is to keep the axis tracking precisely at the sidereal rate, and will also follow any variable rate that is programmed into the servo for purposes of countering atmospheric refraction and other sources of drift. Test results on the new 3600 mount with optional feedback encoder have exceeded all expectations. The measured tracking error was well below 1/2 arc second for a 20 minute time period. With this option, it is now practical to do long period unguided imaging with a fixed setup where other sources of drift (due to polar misalignment, tube flexure, etc) have been minimized or eliminated. Astro-Physics pioneered the use of precision encoders, normally used in the machine tool industry, to help you achieve optimal results during unguided or guided astrophotography. The 9" stainless steel Renishaw encoder that we have chosen is dimensionally stable and has guaranteed subarcsecond resolution over a 24 hour cycle. It is precisely aligned with the corresponding Renishaw Read-Head and tested. This is not a simple tape encoder, which cannot guarantee precise alignment and can shrink with temperature. To further refine the unguided error of the mount, we are adding an all-sky tracking rate to the software, which will minimize RA drift everywhere in the sky. This will allow significant unguided exposure times with a well polar-aligned mount.