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Here
I have mocked up how the PA and its new supporting fork will appear. I
had to counterbalance the weight of the 11" wormwheel for the picture
but the massive weight of the Declination axis will shift the balance
the other way. With a turnbuckle controlling fine altitude adjustment.The wormwheel demands clearance at the rear of the fork. Any base plate overhang at the rear will probably intrude. My 55° latitude and resultant altitude angle increases the clearance problems. The rear 'ears' left from sloping the rectangular fork blades will have to be cut off. Altitude locking bolts will have to be arranged. Which will mean slots in the form of arcs will need to be cut through the 20mm thick aluminium blades.
The 5mm worm support plate shown here will be changed to 10mm for greater stiffness. With a pulley and toothed belt drive system folded over the worm. I can't progress with this detail until I have the stepper motors, pulleys and belts from AWR.
I am torn between resting the fork directly on the 20mm base plate or making the base narrower to pass between the fork blades. I prefer the cleaner look of bare fork blades without a visible joint onto the base plate. I do have some larger 10mm [3/8"] plate which could form a laminated base plate suitable for much greater pier diameters. The actual pier design is still wide open as I have to deal with the raised platform issue. A very tall pier rising from the ground? Or a normal height pier resting on the platform? Both have disadvantages.
If the raised observing platform
becomes a proper carport I could not have a tall, ground-based pier. The sheer
weight of the mounting and OTA doesn't make such a tall pier a sensible
option anyway. So the next best idea is probably a pier bolted down to
the platform floor. When I need critical stability I will just add a
sturdy, removable prop under the pier. Perhaps Rising from a massive concrete paving slab located directly under the pier site on the platform above. This allows the car to enjoy the shelter
most of the time but can be parked elsewhere to allow the floor stiffening prop to be set up.I have considered many pier alternatives over the many years of platform procrastination. A "nested table" arrangement could allow enough clearance for the car while providing completely independent framework support for the pier from below. The base of the pier would be isolated from the platform by allowing clearance as it penetrates the platform surface. This clearance gap detail is a standard construction method commonly used by observatories with wooden floors.
Though most builders use a tall brick or cast concrete pier if the floor is raised much above the ground. Even this has potential problems if the pier foundation is not made literally huge. The heavy concrete or brick pier can actually oscillate like a compound pendulum if excited by touch or motor vibration up at the top. This is even more likely if the sunken foundation can actually rock in the ground. Or if the pier is not made stiff enough. [Or both!]
Something like a 4"x4" timber prop should stabilize the platform mounted pier quite nicely. A pivot bolt between the platform floor joists will allow the prop to be raised out of the way to the north with a rope. All this is largely theoretical anyway. The platform may well be stiff enough to provide all the stability the pier and massive mounting needs. It is not as if I shall be moving about much myself and visitors are highly unlikely. The only likely problem is wind shaking the platform. Wind is uncomfortable so I am less likely to observe or image when it is blowing hard.
Click on any image for an enlargement.
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