Balancing the telescope

MMAO - Balancing the 12" Cave-Cassegrain telescope

Today Eliona and Kai spent from 10 am until after 3 pm with a delegation from the US (Ailanga School Project), learning about their programs and history with the school, and sharing our own experience in the development of the observatory.

From 4-6 we worked with Zacharia and a number of students to balance the telescope before applying the motors. We were confused as to the behavior of the telescope at various angles, but with some diagrams on the white board we recognized that the center of gravity is not symmetrical due to the various, off-center components such as the motor mount block, motor, and spotting scope.

We added the small sandbag to one side of the tube to counter the motor and that helped tremendously. The Dec axis is very nearly perfectly balanced. The RA axis yet suffers from an awkward asymmetry, but we believe it may be due to a flat spot in the bearing or bearing housing itself, due to the tendency to return to the same position after certain rotations, and an audible/physical “click” in the same spot.

As there is nothing we can do to counter this, and it is quite subtle, we moved to mount the motors. The RA motor went on easily, and worked out of the box. The Dec motor was a bit tricky to install, as Kai recalled from his work on this area with Dan. What had not been previously recognized is that the threaded Dec shaft is very subtly bent. This causes an increase in friction at certain points, and the slipping of the stepping motor internal to its housing.

We experimented with a loose connection between the Dec shaft and the slip collar around the RA axis, and that allowed the motor to drive Dec flawlessly. So, the Teflon bushing will likely be replaced with a thin layer of foam instead.

Tomorrow should see the completion of the telescope, and if the clouds clear, first light!

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