Equatorial- Platform

A Dobsonian Telescope has one disadvantage, is does not track the stars. Especialy at high magnifications, this is annoying and diverts from observing.
That can be improved by using an Equatorial Platform.
The working principal of such a platform is described very plastic by Reiner Vogelīs explanation

The Platform in front of the Rocker.

After the base of the rocker is removed, it can be easily fitted to the platform. Centering is done by means of three rollers which are connected turnable to the platform.
Next to them, there are pieces of teflon glued to the borad by means of both sides adhesive tape (this works quite well).

I choose the variation with vertical north segments, similar to the wonderfull platforms offered by Tom Osypowsky

Advantages of this sytem are the vertical transmission of the loads and a slightly compact structure.
On the oher hand, it takes more time and work to manufacture the segments.
As the northern segments move rotating and shifting, the curve is not an arc. One way of generating the curve is to mount the entire upper plate of the Platform in a way, that during routing it can pivot around an axis that is situated where later on the parallel of the earthīs axis is going to be.

To do so, I built a jig for routing the curves. The router is connected to the alienated top slide of my lathe, so it can be positioned very precise.

Caused by the combined roll- shift movement the rollers have to be wider than standart roller bearings:

These are made from 30mm diameter stainless tube and have two ball bearings each.

The lower board with the north- rollers, drive with shifting device and southern bearing.
The spirit levels are very usefull for set up and connected therefore.

The platform is driven by a gear which consists of a planetary gear i=1:20,25 (Ebay), a gearmotor with i = 1:380 and a worm gear with i = 1:40.
A gearwheel is connected to the shaft of the planetary gear and transmits its torque to a gearwheel made from a gear rack connected to an arc segment at the bottom side of the upper board.

To bring back the platform after tracking is done, the entire gear can be shifted slightly to the front in a guiding system made from profile rails, Ebony star and Teflon.

Therefore the lever is moved to the front, by unhanding it, the spring pulls it back into tracking position.

The tolerances inside the planetary gear where quite bugging, therefore I added antother gearwheel with a free wheel in its hub.

This can be turned just in one direction and reduces the tolerances to an acceptable extent.

The Telescope on the Platform.
The entire height of the Platform is 130mm which is 65mm more than the standart base.

Observing with tracking platform is very comfortable, as concentration on the object is not disturbt by moving the scope by hand.
Also it is possible to take planetary images with the webcam:

Saturn on April 15-05 using a Webcam + 2x Barlow, stacked Picture from 120 shots processed with Registax.

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