SkyWalker Functionality


All SkyWalker models share the same two levels of functionality: together with its handpaddle, SkyWalker functions as a stand-alone telescope controller (operating in SkyWalker mode) or, when used with a PC running SkyGuide-Win, a complete full featured telescope control system (operating in System mode).



Features in SkyWalker mode:

In SkyWalker mode, the control system operates without the need for an attached PC. SkyWalker operates autonomously as a versatile telescope and accessory controller. High speed slew, four user selectable pan and slow motion rates and five tracking rates are provided. Numerous telescope control functions (electric focus control, autoguider correction, reticle illumination etc.) are also available. SkyWalker mode requires SkyWalker, motor drivers, and motors (all three integrated in SkyWalker-Servo) adapted to a telescope.

The following specific features are included in SkyWalker mode:

Telescope can be controlled by handpaddle and autoguider (such as SBIG ST-4).
Wide range of track, correction and slew rates:

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Five tracking rates (sidereal, lunar, solar, King, and custom from ephemeral points or offsets) and off (i.e. Drift)
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Four programmable pan/correction rates and accelerations
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Programmable slew rate and acceleration

Quartz crystal time base provides precision timing and accurate tracking.
Control of general purpose peripheral control outputs (dependent on SkyWalker model).
Adjustable Brightness of backlit buttons and indicators.
Neatly connects all components of the telescope control system:

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Connections to items generally used on or at the telescope's optical tube assembly (ex. autoguider, accessory control, handpaddle) are provided at the top end of the SkyWalker enclosure (in the case of SkyWalker1) or the top Servo Drive Unit (in the case of SkyWalker-Servo).
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Connections to items on the telescope mount or elsewhere (ex. motors, encoders, communications) are provided at the bottom.

Proper operation in the Southern Hemisphere
System fault "watchdog" prevents run away failure
Three handpaddle assignable keys with the following programmable functions:

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Invert swaps the polarity of the Up and Down Direction control buttons.
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Mirror swaps the polarity of the Left and Right Direction control buttons.
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Drift turns tracking on/off.
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Assignments that provide control of general purpose peripheral control outputs (dependent on SkyWalker model).

All operational parameters are stored in SkyWalker's nonvolatile memory. These parameters are completely configurable via connection to a PC running SkyGuide-Win:

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Drive gear ratios
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Velocity/acceleration limits
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Default sense of direction buttons
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Handpaddle "assignable" key configuration
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Peripheral output functions (e.g. Focus, Reticle, Dew Heaters, Dome control, electric clutches, etc.)


NOTE: SkyGuide, running on Windows 95, 98 or ME, is necessary to change SkyWalker-mode settings.

Features in System mode:

SkyGuide-Win is the System mode software enhancement for the SkyWalker Telescope Motor and Accessory Controller. In System Mode, the control system operates attached to a PC running our SkyGuide-Win Telescope System Control Software. System mode includes all of SkyWalker mode functionality and adds a versatile and sophisticated, yet easily utilized, set of enhancements. SkyGuide-Win requires a Pentium 120Mhz (or better) PC running Windows95/98/ME (1), video monitor, keyboard, mouse, and serial (RS232) communications port.

SkyGuide-Win and SkyWalker communicate using their respective communications ports. This connection allows SkyGuide-Win to interface to and control motor drivers, SkyWalker's handpaddle, autoguider, optical encoders (for closed-loop control) and various accessories attached to SkyWalker (please visit our SkyWalker1 or SkyWalker-Servo pages for more details).

In System mode, functionality increases dramatically with features such as automatic GoTo (coordinate, Planet or over 16000 deep sky objects), optical encoder support allowing for manual movement, programmable mechanical error correction (PMEC) and control from one of the many commercial or shareware planetarium programs available today running on the same or remote PC. Complete details follow below.





SkyGuide-Win is designed to facilitate use in typical astronomical environments where it is often difficult to interact with a PC. Two convenient ways are provided for the user to interact with SkyGuide-Win:

SkyGuide-Win Console (displayed above). This versatile mouse driven user interface is architected to minimize the need for keyboard entry.
Planetarium Software. SkyGuide-Win can be used with a number of different planetarium software packages to allow the ultimate in "point and click" astronomy.


Summary of System mode features and capabilities:

Control features

GoTo function provides accurate user commanded telescope movement to entered coordinate, named object or "park" position.
Supports optical encoders connected to SkyWalker. These encoders enable SkyGuide-Win to maintain the current telescope position on instruments with clutched axes (where the telescope can be manually moved).
Provides joystick control where smooth and proportional motion follows joystick motion. Joystick buttons have assignable function (similar to SkyWalker's handpaddle assignable keys).
Precisely controls all types of equatorial and Alt/Az telescopes in either open-loop or closed-loop (using encoder feedback) configurations. This includes telescope position limit checking and "orienting" for all styles of telescope mounts. Examples include:

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"Cable wrap up" prevention for fork and typical Alt/Az mounts.
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Automatic "flip" for German Equatorial mounts.
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Definable "user horizon" disallows GoTo destinations below a given altitude.
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Pole (or Zenith) "avoidance".
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The clearance for which limits (ex. the Celestial Meridian for German Equatorial mounts) are avoided is fully programmable separately for East and West limits. Limit overlap is allowed so that there is no inaccessible section of sky.
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Preferred telescope "orientation" (i.e. the side of Pole or Zenith) for GoTo targets.
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For telescope mounts that support passage through the pole (zenith), a "fastest" GoTo mode is available.

Supports position "marking" and arbitrary return to "marked" coordinates. This includes the ability to go back and forth between two coordinates from a single handpaddle button or mouse button click. This feature also accurately reports the delta distance between the last two "marked" coordinates in either "offset" or "position angle and distance" formats.
"Auto calibration" improves GoTo accuracy by first "calibrating" the celestial alignment on a bright star near the GoTo destination.

Object databases:

Planets
The Revised New General Catalog
Index Catalog of Nebulae and Star Clusters
Messier Catalog
All stars magnitude 7.00, or brighter, from the Smithsonian Astrophysical Observatory (SAO) catalog of bright stars.

All telescope control system status is conveniently available from SkyGuide-Win's Console. Much of this status is also reported in host (e.g. Planetarium) software. Status includes:

Celestial (in any Epoch) and Alt/Az coordinates
Standard, Universal, Julian, Local and Sidereal time
Control system status (i.e. system components installed/attached)
Operational mode (i.e. StartUp, Land and Celestial)
Movement mode (ex. Track, Slew, GoTo)
Track rate
Power supply information (i.e. SkyWalker supply voltage and low battery indication with SkyWalker-Servo)

Accuracy and precision

Positioning precision is +/- one motor servo encoder count over the entire sky. Positioning accuracy is limited only by the telescope's gearing and mount accuracy and sturdiness.
The tracking and timing accuracy is set by SkyWalker's high accuracy crystal time-base and not by the PC's (unknown accuracy) time-base
SkyWalker provides a timing precision of 75ms and accuracy of +/-40ms.
Tracking smoothness is exceptional. SkyWalker "meters" the motion out uniformly: PC-generated timing is not relied upon for motion control.

Alignment features

Easy celestial alignment for equatorial or Alt/Az telescopes. Polar alignment is not necessary. Several alignment methods are provided:

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Locate one star for polar-aligned equatorial or permanent telescopes (alignment parameters are saved). The alignment star can be on either side of the Celestial Meridian (i.e. for German equatorial mounts).
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Two stars for arbitrarily mounted Alt/Az telescopes.
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Alignment from "last" position providing for automatic "zero-star" alignment at start-up. Additionally, a "parked" position can be set and alignment automatically completed from this position at start-up. These features provide instant alignment for installations that are not moved between alignments.
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Allows for 3 separate observing sites. Also allows for simple "no site" operation where all features except for "parked" position alignment, Sidereal time reporting and meridian "avoidance" are available (i.e. this is not to be used with German Equatorial mounts).
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"Calibrate" the alignment at any time from coordinate or named object.

Automated polar alignment feature provides quick and accurate polar alignment on equatorial instruments. Note: polar alignment is not necessary to use SkyGuide-Win but many users choose to polar align their instruments to eliminate image field rotation.

Error correction features

Celestial pointing Model that compensates/corrects for:

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Atmospheric Refraction. SkyGuide's refraction correction algorithm is unique in that corrections are applied continuously. The benefit is that tracking is corrected for the effects of atmospheric refraction.
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Precession, Annual Aberration and Nutation into any Epoch

Programmable Mechanical Error Correction (PMEC) removes:

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Mount geometrical errors including non-perpendicular Optical/Dec(Alt) axes and non-perpendicular DEC(Alt)/RA(Az) axes (this feature requires TPoint™ telescope error modeling software).
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Nonlinear driver rates (i.e. drive gear periodic error). "Gear index" sampling in SkyWalker allows for permanently programmed periodic error correction that places no restrictions on control system operation.
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Hysteresis effects (ex. backlash)

SkyWalker handpaddle enhancements: several handpaddle assignable key functions are provided in addition to those available in SkyWalker mode:

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Anchor. Moves the telescope back to the coordinate at which the last direction key was released.
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Hunt. Starts hunt (square spiral) search pattern.
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Wobble. Starts a slow telescope back and forward motion. Useful when observing dim objects.
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Mark. Mark present position for subsequent Return command.
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Return. Return to previously "Marked" position.
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LastGoTo. Returns to the last commanded GoTo destination.
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CalFromEncoders. Updates current position, based on encoder position.
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TimeStamp Accurately records present time and "delta" from last TimeStamp

Peripheral control enhancements: the following peripheral control functions are provided in addition to those available in SkyWalker mode (dependent on SkyWalker model):

Alarm output
Timer output

Useful utilities:

Timer and Alarm functions with warning and linkage to HighDrive (i.e. peripheral) outputs on SkyWalker1.
Time "stamp" feature allows for accurate recording of timing events. Delta between last two "time stamps" is provided.
Full diagnostic capabilities, including:

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Motor position to optical encoder position verification
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Index and limit checking
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Peripheral control output testing
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Autoguider testing
 
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Planetarium software connection tests
 
Initialization and settings:

All operational parameters are completely configurable. In particular, velocity and acceleration can be separately set for tracking, "Pan/Correction" and slewing to 7 decimal digits of accuracy.
Pre-configured settings are provided with Astrometric Instruments' SkyWalker-Servo control system for commercial mounts allowing users to immediately use their telescope control system.
Update of SkyWalker mode settings is very convenient and can be setup to automatically occur every time SkyGuide-Win and SkyWalker connect.
High-performance control on a PC: to achieve low latency (i.e. fast response) and reliable operation, the SkyGuide-Win control algorithm is entirely implemented in an operating system device driver (VxD) (1). With this technology, SkyGuide-Win can reliably service SkyWalker (and its motor drivers and peripherals) with less than 75ms of delay (maximum, even on a Pentium 120MHz system). This results in instant response and none of the side effects associated with the unbounded response time of Windows applications (or DOS applications running under Windows) without device drivers. SkyGuide-Win's device driver explicitly avoids utilizing PC resources that lead to potential response time problems. SkyGuide-Win's technology and design allow it to operate unhindered even when other windows applications are stalled because of heavy workload or while waiting for resources. SkyWalker contains an additional feature that assures reliable operation, in System mode, on Windows-based PCs. This feature is called Sustain mode and allows for uninterrupted telescope control even when the PC is "locked up" while, for example, large images are being downloaded from parallel-port CCD cameras.


(1) Currently SkyGuide-Win does not run on Windows-2000 or Windows-XP. We are actively working on providing support for these operating systems. Windows-2000/XP requires that the "device drivers" be written in a different format than the Windows95/98/ME "Vxd" device driver format. For more information visit the "What operating systems does SkyGuide currently run under?" section of our FAQ page.





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