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The pier for our ridiculously heavy mounting really ought to be a massive concrete construction cast off a ground slab the size of a modest bungalow. Concrete piers are solid but, in controlled tests, have repeatedly proved to be immovable.
In desperation we must look around at our well-heeled [fellow] long focus imagers. Those who regularly nip out into the desert with their costly Ritchie-Chrétien instruments. What do they use under their posh AP mountings? Usually an apparently simple, three-legged pier. Note the emphasis on apparently. Note how the pier legs are large, non-distorting, isosceles triangles in both plan and elevation for stiffness. Not your usual, bolt-on, cast clown's feet attached only at the very bottom of a spindly pier pipe.
Portable Telescope Piers from Advanced Telescope Systems
The triangular legs reach well up the sides of the pier pipe where they are hinged very firmly into place. Pier pipe diameter is not your 'common or garden' 4" water pipe. These pier pipes are deliberately made large to avoid flexure. So large that they could be used for people smuggling on the return trip from the desert. I jest, of course, but you get the message. Where pier pipes are concerned then BIG is BEAUTIFUL.
What can we learn from this? That bigger is even better if weight must be kept manageable. Steel ventilation ducting comes in various sizes in 2 meter lengths. A 12" diameter tube makes good sense when wall thickness [and greatly increased weight] is denied to us. Our thin steel pier pipe is not going to be the stiffest "factory chimney" around. So it will need careful reinforcing at stress points to avoid ovality and other distortions.
Thick plywood can be laminated into thick, internal circles and fixed where it really matters. Studding can be used in compression between these baffles to tie the thick top flange to the upper leg hinge points. Multiple screws can be added to lock the thick disks into place through the walls of the tube. Because we have a free choice, we can make the pier pipe just clear the ground to greatly increase the area of the vertical leg triangles. The more even-sided a triangle, the stiffer it becomes. The desert imagers demand portability and mobility for the shortest possible pipe length. We cannot afford the luxury of lightness.
Thick plywood can be laminated into thick, internal circles and fixed where it really matters. Studding can be used in compression between these baffles to tie the thick top flange to the upper leg hinge points. Multiple screws can be added to lock the thick disks into place through the walls of the tube. Because we have a free choice, we can make the pier pipe just clear the ground to greatly increase the area of the vertical leg triangles. The more even-sided a triangle, the stiffer it becomes. The desert imagers demand portability and mobility for the shortest possible pipe length. We cannot afford the luxury of lightness.
The image shows the potential for a fully triangulated four legged pier. Tension cables, metal strips or pipes can be stretched from the upper cross down to the feet. Providing excellent resistance to torsion around the pier relative to the feet on the ground.
We fully intend to balance our heavy mounting and telescope centrally over the pier pipe. So no cantilevered loads are expected. Any tendency to tip will be the result of pointing the telescope to different parts of the sky and [quite probably] wind gusts.
Moving the entire instrument on wheels might be very risky with so high a center of gravity for a large refractor. All the mass is perched up on high. Though the fully triangulated legs become quite rigid, when done properly, they will not be modest in size. Which will make them rather 'bulky' in the dark. But we must totally avoid our Saturn 5 'rocket' from toppling.
The answer may be to ensure a flat running surface [or rails?] without bumps to cause sudden braking lower down. I speak from experience in rolling my heavy refractor pier and mounting around the garden on sack truck wheels. My observing space is not flat and is a mixture of lawn and bumpy gravel with a slope to boot. One hand has to constantly support the top of the pier to avoid it tipping right over on top of me during maneuvers. As I drag the pier in reverse I wear sensible, steel toe-capped work shoes. Just dropping a heavy counterweight on your foot could easily hospitalize you. What damage do you think a massive mounting and heavy telescope can do? Be safe.
If the pier has to be moved then the telescope really should be removed first. The heavy mounting is still up there in the clouds which will need great care. The counterweight will throw the balance off too and greatly increase the mounting's moment in the event of the pier tipping even slightly. Perhaps it would be safer to be less ambitious regarding true mobility? Though four legs/feet will go a very long way to making any significant movements safer.
I prefer four-legged 'tripods' [quadropods?] to three as they offer a further plane of stiffness and greatly increased resistance to catastrophic tipping. See the associated images for the doubling of the support base between any 3 and 4 feet arrangement at exactly the same radius from the pier center. On non-rigid ground, four legs will easily adapt to the ground by sharing the pressure equally on their foot pads. Local foot or leg adjustment will be needed for leveling anyway.
Another tripod-pier with similar characteristics:
http://schickworld.com/astronomy/Resized/Monolith.png
Some commercial piers are using turnbuckles in cables to steady the pier pipe but using conventional clown's shoes for the feet. The problem with this arrangement is the poor resistance to torque around the head of the pier. The piers with triangulated legs offer far greater torque control. I built a tripod for my ATM 5" f/15 refractor in my youth from 2" scaffolding poles with heavy angle alloy bolted to a thick plywood disk. Even with the light 1lb force required to move the telescope over most of the sky the tripod still 'gave' slightly to azimuth movements. Requiring I overshoot and let the tripod "unwind" itself to its relaxed condition.
I have a heavy Bogen video tripod with duplicated legs but it falls down on stiffness when the lower legs are extended. The leg extensions are of quite large diameter for a photo tripod but undo the triangulation offered by the stiffer upper legs. Here it is shown beside the road at the top of a local hill with the Vixen 90/11 aboard for dawn solar viewing. It worked for my afocal snaps but is not something to try in the slightest breeze!
Moving the entire instrument on wheels might be very risky with so high a center of gravity for a large refractor. All the mass is perched up on high. Though the fully triangulated legs become quite rigid, when done properly, they will not be modest in size. Which will make them rather 'bulky' in the dark. But we must totally avoid our Saturn 5 'rocket' from toppling.The answer may be to ensure a flat running surface [or rails?] without bumps to cause sudden braking lower down. I speak from experience in rolling my heavy refractor pier and mounting around the garden on sack truck wheels. My observing space is not flat and is a mixture of lawn and bumpy gravel with a slope to boot. One hand has to constantly support the top of the pier to avoid it tipping right over on top of me during maneuvers. As I drag the pier in reverse I wear sensible, steel toe-capped work shoes. Just dropping a heavy counterweight on your foot could easily hospitalize you. What damage do you think a massive mounting and heavy telescope can do? Be safe.
If the pier has to be moved then the telescope really should be removed first. The heavy mounting is still up there in the clouds which will need great care. The counterweight will throw the balance off too and greatly increase the mounting's moment in the event of the pier tipping even slightly. Perhaps it would be safer to be less ambitious regarding true mobility? Though four legs/feet will go a very long way to making any significant movements safer.
I prefer four-legged 'tripods' [quadropods?] to three as they offer a further plane of stiffness and greatly increased resistance to catastrophic tipping. See the associated images for the doubling of the support base between any 3 and 4 feet arrangement at exactly the same radius from the pier center. On non-rigid ground, four legs will easily adapt to the ground by sharing the pressure equally on their foot pads. Local foot or leg adjustment will be needed for leveling anyway.
Another tripod-pier with similar characteristics:
http://schickworld.com/astronomy/Resized/Monolith.png
I have a heavy Bogen video tripod with duplicated legs but it falls down on stiffness when the lower legs are extended. The leg extensions are of quite large diameter for a photo tripod but undo the triangulation offered by the stiffer upper legs. Here it is shown beside the road at the top of a local hill with the Vixen 90/11 aboard for dawn solar viewing. It worked for my afocal snaps but is not something to try in the slightest breeze!
Click on any image for an enlargement.
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