8.02.2021 Early musings on cross-axis mounting support.

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English, Cross-axis mounting:

North or south mounted RA drive on the [planned] cross-axis mount?  A wireless mouse and keyboard require no close proximity for an imaging desk. Though they still have a minimum footprint. The high res. monitor still needs an HDMI cable to the laptop and adequate support. It all has to be carefully considered.

The rough drawing [Right] shows potential cross axis mounting support seen form the west. Two A-frames of 4"x4" timbers are raised at north and south. Inside the building but isolated from it. The A-frames provide the lateral rigidity for the Polar Axis. Though some lateral adjustment will be needed for polar alignment.

I imagined a [very stiff] curved plywood [laminated] bearing support above but well attached to the northern A-frame. The curved plywood structure would provide maximum telescope clearance while following the curve of the dome. The height and spread of the northern A-frame can be chosen to match the needs of the curved "extension." Probably reaching obs. wall height before the plywood takes over.

N-S stiffness can only be provided at the lower, southern end of the very long, Polar Axis. Where all the mounting and telescope loads must be safely resisted without causing a major obstruction downstairs on the ground floor. Nor by directly connecting it to the building. 

The fact that the observatory is raised demands serious attention to the support geometry. I have no plans to build anything in concrete, brick or blocks. Preferring timber and triangulation. Even plywood cladding where it makes most sense.  

Options exist for below-floor bracing. Where they won't inhibit free movement upstairs on the observatory floor. The lower [South] PA bearing can be placed at many different heights. Raised well above the obs. floor or placed low down. Even underfloor. Though the stepladder/stairs may well dictate certain arrangements are better than others. Each choice affects the geometry of the support system under the fixed 55° PA angle. The PA can be any suitable length but, again, will affect the support geometry.

The next drawing [left] has to be imagined in 3D. It shows the same arrangement as the drawing above but seen at 90° to the first. The two A-frames are upright in a N-S sense. The northerly A-frame much taller than the southern. I should really have drawn the northly one much taller.

Bracing from lower down to higher up on the A-frames automatically provides triangulation in several planes. A horizontal cross beam, [or beams] just under the obs. floor, would enjoy the same gain in stiffness by triangulation from rising braces. [Shown, at left, in red.]

I'm hoping the increased and much rounder 4.3m footprint will feel more like a cavern in the dome and downstairs. At least in comparison with the present 3m octagon based observatory. With its very wide, [2x10] timber, top ring reducing the usable floor space even further. The [present] huge, pyramidal, central pier also sets limits on the ground and obs. floor arrangements. 

A cross-axis is much more bulky than a GEM on a central pier but we shall see. I have no intention of building a cross axis without doing extensive "homework" first! Which usually just means daydreaming in my case. New ideas just pop into my head if I ignore the problem and let it rattle around for a while. I can easily make mock-ups using battens. To get a feel for dimensions, bulk and telescope sweep. I plan to do so on the ground using the arc templates to indicate the dome curvature. Just to get a feel for a suitable length for the PA.

 

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