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Amateur Telescope Making

20 Inch f/4.5 Alt-Az

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Here is the base of the scope. In the center is the azimuth encoder, housed in a plastic box. The white box to the right is a RJ-11 connector box. In the upper center (and the pic below), the rear half of the azimuth drivetrain is shown.

The motor drives a timing belt, which drives a shaft (at the left). The shaft is captured between 3 bearings. The top bearing drives the azimuth table. The other two bearings force the shaft against the top drive bearing. These stepper motors have a 30:1 gearbox attached to them. (Note: the steppers have been replace by servo motors)

The large bearing in the center of this picture is one of three that the azimuth table rides on. The drive shaft is pinched between this bearing and two others in an adjustable pressure housing. Pressure is adjusted to allow the scope to be moved manually (the table bearing slips on the drive shaft), but when the scope is released, the remaining friction between the shaft and bearing is enough to overcome azimuth inertia, and move the table.

The base with the azimuth table in place. A bar attached to the inside of the azimuth table, connects with the azimuth encoder to turn the encoder shaft. The wiring for the encoder and power connection is routed along the bar to the outside controllers.

In the center right of the photo is the altitude motor and the altitude drivetrain. The 30:1 gearbox is shown attached to the motor. Note that this picture shows the old altitude drivetrain, the new one can be seen in the cable drive section.