Shibumi Astro Engineering Light-Duty RA Axis Anti-Backlash Kit for EQ8-R

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Shibumi Astro Engineering Light-Duty RA Axis Anti-Backlash Kit for EQ8-R

Replaces the OEM RA or DEC worm block assembly, motor timing drive belt and pulley, and associated fasteners. The worm gear is flexurally mounted into mesh with the worm wheel, resulting in minimal backlash and improved transmission stiffness. An integrated meshing force guide is provided. Mesh clearance adapts to temperature fluctuation and wear and will be maintenance-free in most use-cases. Two versions of the kit are available, light-duty (LD) and heavy-duty (HD). The kit is available for any EQ8 mount model, and for either RA or DEC axis. Both LD and HD versions include precision ground worm gears made from hardened 440C stainless steel running in upgraded bearings, with spring-loading of the worm mesh with the customer’s existing worm wheel. Upgraded timing drives and where appropriate a belt tensioner are included. The OEM stepper motor and compliant motor mount are retained. The ‘Freedom-Find’ encoder read-head, if fitted, is mounted in the same way as on a standard EQ8.

LD versions are designed to provide economical and easy to fit backlash control for mounts used for light to medium payloads. A more precise zero-backlash timing drive with GT2 belts andclamp-hub timing pulleys is included for LD kits for the RA axis on EQ8’s, and for both axes on EQ8-R’s.

HD versions are optimised for greater transmission stiffness and lower backlash for use with high payloads. These cost more, and an automated gear burnishing operation is mandatory after installation to match the new worm gear to the existing worm wheel. They use a redesigned larger, stiffer worm gear, heavy-duty radial/axial worm bearings, larger timing drive pulleys housed in new roomier plastic covers. A relocated worm index switch is used in the RA axis kits. The DEC axis kits substitute a folded timing drive configuration for the DEC axis kit (similar to the EQ8-R) in place of the direct-driven DEC worm used in OEM EQ8 mounts.

HD versions exclusively offer the choice of either a 1:1 timing drive ratio (as per the OEM mount) or 1.5:1 ratio (which reduces maximum slewing speed but boosts drive torque and tracking smoothness.)

Perhaps the greatest weakness of the Skywatcher EQ8 mount family is the design decision to use fixed-centres worm gearing implying that significant backlash must always be present. Attempts to adjust out all mesh clearance run the risk of gear jamming at low environmental temperatures. The present development was born out of a frequently expressed wish on the Skywatcher EQ8 Forum for a user-installable solution for taming the backlash in this family of mounts. While SAE has offered an alternative form of anti-backlash gearing for a number of years, this required shipping of mounts to our facilities in Ireland.

These new kits all include refined spring-loading of the worm gearing mesh, with a hardened and ground worm gear, upgraded worm gear bearings, and a zero-backlash timing drive between worm and drive motor. The existing worm wheel, drive motor and motor coupling is retained. This package is quick and simple to install for users with basic mechanical skills, easy to set up, and eliminates the need for periodic mesh adjustment. Light-duty (LD) and heavy-duty (HD) versions are offered; the latter include more features but cost more and take longer to install.

The degree of backlash reduction experienced varies according to the condition of the user’s mating worm wheel, but measured backlash will generally be less than 5 arcseconds after a period of bedding-in. Bedding-in instructions are provided.

This kit is a key component in a set of upgrades that allow the value-oriented Skywatcher EQ8 to be made suitable for remote unattended astro-imaging service.

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