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Amateur Telescope Making

20 Inch f/4.5 Alt-Az

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How it works:

An aluminum band (1/16" thick) is wrapped around the inner rim of the bicycle wheel. The inside of the band (the side riding against the wheel rim) is coated with a thin layer of adhesive delrin as a bearing surface. The ends of the band are connected by a tensioning adjustment, to either tighten, or loosen the band against the wheel rim.

A cable is attached to the band on each side of the tensioning adjuster and wraps around the outside of the band, and twice around a drive roller. The band effectively becomes locked in position by the cable and moves at the rate of the drive motor. When the scope is moved by hand, the band slips against the wheel rim, but when released the band resumes moving the scope in altitude.

The scope moves in altitude much like a scope riding on teflon bearings, but the increased surface area of the band's delrin bearing surface allows a greater amount of weight imbalance in the OTA.

At the upper left, the drive roller is shown just below the trunnion roller. At left, the cable is shown riding on the outside of the band between the roller and the wheel rim. The bottom photo shows the tensioning adjuster and the cable attachment points. The cable shown at left is standard aircraft cable, however, the best cable was found to be galvanized aircraft cable with a vinyl coating. It grips the drive roller with less tension and never slips.