Astrometric Instruments' support FAQ:


This FAQ is divided into the following sections:

SkyWalker hardware installation and use.

SkyWalker functionality.

Optimization of Astrometric's Telescope Control System performance.

SkyGuide Telescope Control System software installation and use.

SkyGuide-Win is provided for users of non-upgraded legacy (i.e. pre-2004) SkyWalker systems. SkyGuide-Win will only run under Microsoft Windows 95, 98 or ME.

Legacy (i.e. pre-2004) SkyWalker systems can be upgraded to full and complete current functionality with the S-Box accessory. The S-Box allows for SkyWalker control from all versions of Microsoft Windows (using our Maestro software). The S-Box also allows for stand-alone operation (i.e. without an attached PC) using our HP2 handpaddle.

SkyGuide-Win FAQ items:


Problems with motor stalls with SkyWalker-Servo or SkyWalker2

Due to retrofit kit installation problems. The mechanical coupler that connects the drive unit to the Losmandy worm shaft needs to be carefully "lined up". The cover over the worm should be removed (with the small Allen key wrench provided in the kit) and the alignment verified. In other words, there should be little or no offset between the disk portion of the coupler that is on the drive unit shaft and the disk portion on the mount's worm shaft (refer to the picture in the kit's installation instructions). The alignment can be adjust to some degree by loosening the screws that hold the drive unit to the mount, moving the drive unit to the position of best alignment and re-tightening the screws. The alignment can also be adjusted via adjustment of the worm's "bearing blocks". Refer to the next item for instructions on this.

Due to excessive gear friction. It is very important that the following are observed when installing the retrofit kit "drive units":

  • For SkyWalker2: when SkyWalker's power is turned off, the slow motion knob on the drive unit should turn very freely. If any friction is detected this is a sign of a problem with the adjustment of the mount's worm. Note: the drive unit has a 3:1 reduction from the slow motion knob to the mount's worm, hence any friction detected at the slow motion knob means ~3x friction at the worm!
  • For SkyWalker-Servo: with the system powered-up and operating in Land mode, the MotorLoad values on the Status Console Tab should not exceed 1000 when tracking.
To remove friction in the mount's worm:
  1. Verify that the worm and worm gear are properly lubricated. Use white lithium grease to assure low friction. If the existing lubrication is "dried up" it may be necessary to clean the gears of the old highly viscous lubrication before applying fresh lubrication.
  2. Assure that the worm is not "pressed" into the worm gear. Sometimes this is done to lessen backlash but should never be done to the extent that high friction at the worm results. This will lead to motor stalls and excessive gear wear. The worm is adjusted by loosening the Allen screws (using the large Allen key wrench supplied in the kit) under the "bearing blocks" that hold the ends of the worm shaft. The bearing block furthest from the Drive Unit should be loosened so that it is free to move but the other bearing block should only be loosened to the point that it can "pivot". The adjustment is made by performing the following simultaneously:

    1. Press and hold the bearing block that is furthest from the Drive Unit towards the Drive Unit. This removes "end play" in the worm bearings and will minimize backlash.
    2. Press the worm all the way into the worm gear ONLY to get a gauge of what "all the way into" is.
    3. Relieve the pressure of the worm against the worm gear and tighten down the bearing blocks.

    This last step is subjective and it will be necessary to accumulate an understanding of what "looseness" is sufficient through some iteration. You can gauge that the adjustment did not introduce excessive friction by turning the slow motion knob on SkyWalker2 or viewing the MotorLoad values for SkyWalker-Servo (as mentioned above).

    Many Losmandy users have noted that the "clearance" between the worm and worm gear varies around the rotation of the worm gear (i.e. is a function of the hour angle in RA or Declination in Dec). It is therefore recommended that SkyWalker be used to move the worm gear to a half dozen equally spaced positions around the worm gear and assure that the friction is minimal (and readjust as necessary) at each position. Make these movements under SkyWalker control, not by manually grabbing the telescope and moving it, since the later will not actually change the gear position.

Due to telescope imbalance. No more than a slight imbalance should be allowed in either mounting axis. If the clutches are completely loosened on a given axis the imbalance should not be more than what leads to the telescope slowly rotating "away" in that axis. Generally on Losmandy mounts RA is left slightly unbalanced so that backlash correction is not necessary. Backlash correction can be troublesome on Losmandy mounts because of the variation in backlash around the gear (i.e. it is not a fixed value and changes with hour angle in RA and with Declination in DEC). This is due to the variation in "clearance" mentioned above.

Due to Low battery voltage. SkyWalker is designed to work down to a supply voltage of 11.0v. A voltage below this will result in poor performance. This voltage is low enough that lead acid batteries can be used over their full operating range. It is possible that voltage less than 12.0v will, together with some measure of other problems as listed above, cause stalls. A related requirement is that no substitute for the power cable and in-line fuse supplied with SkyWalker should be used without first consulting Astrometric Instruments.

Use of USB-to-RS232 converters to interface SkyWalker to Client software such as Maestro.

SkyWalker and Client software will reliably communicate with PC serial ports provided by USB-to-RS232 converters. We have tested and recommend the following converter models:
  • Belkin F5U109
  • Newer (post-2010) Keyspan USA-19HS
  • Trendnet TU-S9
We have experienced problems with some other brands of converters with some PCs. While other converters have been shown to work with most PCs we have found PC/converter combinations that will not reliably communicate over extended "up time" periods or will fail during SkyWalker's firmware upgrade (which is particularly challenging to the communications hardware because of the large data packets transferred). We have never encountered any problems with the converters listed above.

Using SW_Firmup, as a Maestro alternative, to upgrade SkyWalker's firmware

SW_Firmup is a very simple SkyWalker Client program that can be used as an alternative, to Maestro, to upgrade SkyWalker's firmware. To use SW_Firmup, proceed as follows:
  1. Right click on this link and choose "Save as" and save SW_Firmup.exe to a folder on your PC where you wish to place SkyWalker's firmware upgrade files.
  2. Extract the upgrade files, for the firmware version you wish to upgrade to, into the same folder that you placed SW_Firmup.exe in the last step.
  3. Connect SkyWalker to a free serial port on your PC.
  4. Run SW_Firmup and enter the serial port number that SkyWalker is connected to and the firmware version that you wish to upgrade to when prompted. SW_Firmup will commence upgrading SkyWalker's firmware and provide status as the upgrade progresses. Note: the upgrade can take many minutes to complete. Also note: you can run SW_Firmup by simply double clicking its file name from File Explorer or My Computer.

How to backwards-upgrade SkyWalker's firmware to an older version

Astrometric's alternative SkyWalker firmware upgrade utility, SW_Firmup, can "backwards" upgraded SkyWalker firmware as follows:
  1. Download and extract the upgrade files, for the firmware version to program "backwards" to, into c:\Program Files\Astrometric\Maestro\SkyWalkerUpgrades (if they are not already there). These files can be downloaded from our support/upgrades page.
  2. Download SW_Firmup.exe (from the link above) into the
    c:\Program Files\Astrometric\Maestro\SkyWalkerUpgrades folder.
  3. Open a Command Prompt window and enter the following commands:
    1. c:
    2. cd \Program Files\Astrometric\Maestro\SkyWalkerUpgrades
    3. SW_Firmup.exe -force
  4. You will now be running SW_Firmup. Follow the directions that the program presents to complete the upgrade.

Better pointing accuracy: procedure to remove non-orthogonality error

There are several errors in telescope systems that lead to pointing errors. These include gear errors (such as periodic error and backlash), flexures (such as tube sag and axis bending), "hysteresis" errors (such as mirror flop in SCT tube assemblies) and geometrical errors in the mount. To control typical gear errors you can use SkyGuide's periodic and backlash gear error removal features. To control flexures and geometrical errors you can use TPoint. To control hysteresis errors you can use techniques detailed by several people on various Internet news groups.

We have found that simply "tuning out" the primary geometrical error, which for a German Equatorial mount (GEM) is usually optical-axis to DEC-axis non-orthogonality, can dramatically improve pointing. In fact, this step, together with remedying mirror flop, can bring your system to a level of pointing accuracy that may render the expense and difficulty of TPoint unnecessary.

The basic approach to improving optical -to- DEC orthogonality is to view a fixed, and very distant, object from either side of the meridian and "shim" the optical tube assembly (OTA) until the distant object is centered from both viewing positions. It is most convenient to choose a distant object that is stationary (or nearly so). Anything terrestrial is generally too close and error will be introduced due to parallax. A star very close to the Celestial Pole is optimal.

There are other variations of this method mentioned on the Internet. One popular version describes a procedure where the telescope is first approximately polar aligned and then Polaris is viewed with the telescope alternatively at an hour angle of +6hr and then -6hr. This method is less accurate than the method described here since it is not solely dependent on optical -to- DEC non-ortho error but is also dependent on RA -to- DEC non-ortho error. Note: all of these methods will be effected by mirror flop therefore that problem, if present, should be addressed first.

Our optical-axis to DEC-axis non-orthogonality removal procedure:

  1. Roughly point the polar axis of the instrument at the intersection of the Celestial Meridian and the Celestial Equator (see definitions in chapter 3 of the "SkyGuide User's Manual" if necessary). This first step is the most difficult however the accuracy that is required is very loose (within a few degrees is OK). You can accomplish this first step as follows: 1) approximately aim the polar axis at the Equator/Meridian intersection, 2) approximately level the base of the mount, 3) set the DEC axis horizontal (i.e. pointing East/West), 4) while keeping RA stationary, point the telescope at a DEC setting circle value equal to your latitude minus 90 degrees (for example here at 42 degrees North the setting would be -48 degrees), 4) using only the Altitude and Azimuth adjustment knobs on the mount's base, center Polaris (or other "close to pole" star) in the telescope's eyepiece.
  2. Startup SkyGuide but DO NOT enter Land mode (yet).
  3. Go to the Settings/StartUp/Motors/SpecsRA Instrument Display Page and note the "StepsPerRev" value. For SkyWalker2 on the G-11/CI700 this will be 6,912,000. For SkyWalker-Servo on the G-11/HGM-200/CI700 this will be 14,400,000
  4. Startup SkyWalker and enter Land mode from within SkyGuide.
  5. Put the system into Drift (i.e. select a TrackRate of Drift).
  6. Re-center the star (if necessary) using Altitude and Azimuth adjustment knobs on the mount's base and go to the Status/Diagnostics/Motors&Encoders Instrument Display Page and press "Zero" next to the MotorRA value.
  7. Using the handpaddle, in Slew mode, "flip" the telescope so that it points at your chosen star from the other side of the mount. To be certain that you have completed nearly a 180 degree flip verify that the MotorRA value on the Status/Diagnostics/Motors&Encoders Display Page is nearly equal to the value you recorded in step #3 divided by 2 (i.e. 1/2 of a "rev").
  8. Shim under the OTA (towards the front of the tube or towards the rear as necessary) to bring the chosen star ONE HALF of the way back to centered in the eyepiece.
  9. Using the Altitude and Azimuth adjustment knobs on the mount's base, re-center the chosen star in the eyepiece.
  10. Repeat steps 7, 8 and 9 to improve accuracy.

Better pointing accuracy: backlash considerations

Backlash in a telescope's drive gears can lead to pointing inaccuracy. SkyGuide's backlash correction feature can be employed to reduce the effects of backlash error however on some mounts the backlash can be inconsistent around the worm gear. For example, on mounts that have some degree of play in the worm gear such that the gear is not perfectly centered, but rather can "shuck" from side to side (by even a very small amount), the backlash will vary around the gear from a potentially large value at one position to nearly nothing when the gear is rotated half way around. This problem (for G-11 users) was mentioned in the "Problems with motor stalls with SkyWalker-Servo or SkyWalker2" FAQ item above.

Using SkyGuide's Consistent Approach GoTo feature (available in SkyGuide 2.10 or later), GoTos always approach the target "consistently" (i.e. headed in the same direction). With well balanced telescopes, this mitigates the effects of backlash by always "taking" the backlash up in a consistent direction. It also assures that after a GoTo there is no "tracking dead time" associated with RA backlash. Using Consistent Approach GoTo is preferable to using backlash compensation on mounts that have inconsistent backlash around the worm gear's revolution.

Regardless of weather SkyGuide's Consistent Approach feature is used or not it is good practice to approach all objects, for which calibrations and alignments are completed from, headed in the direction West in RA and consistently North or South for Dec. West in RA so that tracking motion starts with no backlash to be taken up and consistently in DEC so that alignments are free of backlash error.

Communications problems between SkyGuide and SkyWalker

PC "goes to sleep". It is typical to have problems with communications faults when using laptops setup to "go to sleep" or go into a low power mode after some amount of time with no user input. Laptops may have to be setup to not go to sleep after a fixed interval.

Communications faults in Windows98/ME. We have encountered problems, under Windows98/ME (but not Windows95!), where communications faults occur if the PC has been running Windows for an extended time (a week or more). Rebooting Windows has always cleared up this type of problem. With SkyWalker's Sustain mode allowing for occasional communications hiccups this issue is hardly ever a practical problem.

PC must be 120MHz Pentium or faster. We test SkyGuide releases on a 120MHz Pentium PC. Using a PC slower than that is not recommended and could lead to problems with communications faults.

A 16550 UART (or better) in the PC's communications port used to connect to SkyWalker is recommend. All modern communications ports meet this criteria however older systems may not be equipped with 16550 (or better) UARTs.

IRQ necessary for communications port. In order to work properly, SkyGuide and SkyWalker must be connected via a RS232 port that has interrupt support AND the RS232 port must be assigned a unique IRQ number. This is because SkyGuide must receive an "interrupt" from SkyWalker with low latency for SkyGuide's device driver to "service" SkyWalker fast enough.

PC COM1 and COM2 ports almost always meet this criteria however there are several "add on" serial port adapters based on PCMCIA/PC-Card/USB that do not provide a unique IRQ for the associated communications ports. If you need to add a serial port to your machine consider one of the ports list on our serial port vendors web page.

Another instantiation of this issue is that SkyGuide can report "Data corruption problem with SkyWalker communications" if the PC's communications port does not have direct IRQ support. You may also find that a communications port will work fine with other serial communications applications (such as terminal emulators) but fail with SkyGuide. Again, this is likely due to the lack of direct IRQ support.

Finally, we have traced communications problems to IRQ conflicts. We have, for example, seen situations where a customer has sound hardware (e.g. Soundblaster) that is setup to use the same IRQ as a communications port.

If SkyGuide will not establish communications with SkyWalker. Other than the above mentioned direct IRQ support requirement, and other than cable problems, we have encountered the following communications problems over the years:

  • As mentioned above, Windows will get "bogged down" over time (particularly Windows98/ME) and require a reboot. This has only been noted on machines that remained booted for weeks on end.
  • It is possible that the communications port was used by another app that didn't properly close it. The cure is to reboot the PC. Improperly terminated DOS programs will do this.
  • One of our customers had a problem where communications faults would happen whenever a scroll bar was dragged or a switch between applications on the desktop was done. This was traced to a VGA card that when replaced the system worked fine.

Can a USB-to-RS232 adapter be used to interface SkyGuide to old SkyWalker models?

Not reliably. SkyGuide used a device driver (acontrol.vxd) that runs within the Win95/98/ME operating system and provided very low latency control of old SkyWalker models. Because low latency is required, USB-to-RS232 converters do not work reliably with SkyGuide and the system will regularly enter Sustain-mode. With new SkyWalkers (post-Oct-2004 or older SkyWalkers that use the S-Box) the low latency control is not between the PC and SkyWalker but contained entirely within the hardware and the higher latency in USB-to-RS232 conversion is tolerable.

GoTos are way off, perhaps even in the wrong direction

In the SkyGuide installation process you are queried concerning the mount that SkyWalker is installed on. Your answer is used to setup the proper default initializations for your system. If the incorrect default was selected during installation then the system will not operate correctly.

There are additional settings within SkyGuide that are important for telescope mounts that have restricted movement (e.g. with respect to the Celestial Meridian). If these settings are incorrect, SkyGuide can, for example, attempt to do a "Meridian flip" at the wrong time. The requirements for these settings are detailed in the "SkyGuide User's Manual" chapter 2 in the "Start-up checklist" section. Site information (specifically Longitude) and the PC's clock must both be reasonably accurate. Refer to the "Setup the site (i.e. observing location) information" and "Verify that SkyGuide's sidereal time is correct" items in the "Startup checklist" section of chapter 2 for more information.

More detail: Accurate time is not necessary for all types of celestial alignment, however, if you use any type of Meridian Avoidance the PC's clock, time-zone setting and site's longitude should be reasonably accurate (to a few minutes of time and to a few tens of minutes of arc) so that SkyGuide can properly calculate sidereal time. SkyGuide's calculation of the position of the Meridian uses sidereal time. Failure to adhere to this guideline can result in SkyGuide not properly avoiding the Meridian and possibly, for example, "driving" the telescope into the pier.

If you have a custom setup be sure to go through the "Startup checklist" section of chapter 2 and all of chapter 4 ("Startup Settings") in the "SkyGuide User's Manual".

If you have a standard mount then ALL of the startup settings, except for communications port selection and site details, are already made for you as part of the default initializations mentioned above.

Why do SkyGuide's "limit avoidance" features not work?

Assuming that default settings were properly chosen and site/time settings are correct (as describe in the previous item) limit avoidance should work fine. NOTE: There is no Limit Avoidance prior to Celestial alignment Before SkyGuide is aligned it has no knowledge of the absolute direction that the telescope is pointing hence it can not avoid limits. The same is true when using the system without a PC (i.e. using SkyWalker only in SkyWalker mode).

How is the "Local Host" interface for TheSky v5 setup?

Refer to the section "Setting-up to use Local Host software" in chapter 18 of the "SkyGuide User's Manual" for complete instructions.

Note that if you install TheSky AFTER you install SkyGuide that a critical file that SkyGuide uses to communicated with TheSky will be clobbered (i.e. overwritten). The fix is to simply reinstall SkyGuide (and select "Keep existing settings" in the SkyGuide installation program).

The text on SkyGuide's Console is too big

This will occur if the PC's Display Adapter is set for "large fonts". To work around this problem take the following steps:
  1. "Right click" anywhere on the Window's desktop.
  2. Select "Properties" from the menu that pops up.
  3. You should now have the "Display Properties" dialog box visible. Click on its "Settings" tab.
  4. In the "Font size" area select "Small Fonts" from the drop-down menu.
  5. Click OK. You may be asked to reboot your machine in order for the settings to take effect.

The values I enter into SkyGuide's Instrument Display do not "stick"

The "OK" button must be pressed to get a value in the Instrument Display to be saved. If you change the value and press the "UP" button the new value will not be saved. Think of the "UP" button as "Cancel what I was doing and then go UP".






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