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Next I need to provide adjustable resistance to the applied end loads on the worm housing. I am trying to find a way to stiffen the resulting structure in all planes. Pivots are localised resistance with high local loads. Which usually means unwanted flexure. How to spread the loads to become a solid mass or geometrically stiff arrangement with all the resistance, thus afforded?
For
example: A hinge can be replaced, or reinforced, by a flexible sheet of
material. A flat sheet is extremely resistant to distortion in its own
plane. Much less so, perpendicular to the deliberately flexible sheet.
How to constrain such flexible "hinges" so that they do not twist at right
angles to the resistance provided? While still delivering the desired compliance?
Spacing
can be used to stiffen an assembly where it replaces a short but solid
arrangement. The so-called moment of the structure can be increased
dramatically. Much like improving the depth of a beam raises stiffness
out of all proportion to increasing its width. Though the resulting beam must be
restrained from twisting itself into the weaker plane. Cross bracing or "egg box" construction are popular.
A mounting can use well spaced bearings of less demanding quality. Rather than oversized, high quality bearings in a short but stiff arrangement. Opposed, taper roller bearings in a short housing have inherent resistance to flexure. A compact and lighter design is possible at the expense of demanding much greater precision and expensive bearings.
The much longer, "low tech" arrangement of spaced bearings is bulky and the supporting structure potentially flexible. The beam between the bearings must be very stiff. Many older [now antique] mountings on professional refractors used widely spaced bearings and cast iron housings. Even in smaller apertures the design philosophy holds true amongst professional telescope builders. Naturally the sheer size weight and bulk made them automatically needy of observatory protection. Those who could afford these costly mountings and refractors could afford the protection they demanded.
The modern amateur astronomer makes no such concessions and demands the utmost portability. Literally at any price! Observatories are expensive and static and are often subject to light pollution. So amateurs work outside their homes and house the high tech gear indoors. Or in the garage. Or take to the darkness of the countryside. Which sets a severe limit on what can be easily lifted. Upmarket mountings provide the wealthy amateur with the goods. Often at a total cost of buying a house in some markets.
I have a protective observatory and lifting aids like winches and pulleys. My low tech mounting must overcome flexure, where possible, but I have no absolute need lightness and compactness. Though I'd prefer both if they were free of other major handicaps. Like being hideously expensive!
Back in my youth I constantly read the ATM series of three volumes. Where amateur astronomers cast concrete mountings. Or welded up massively heavy constructions.This is almost unheard of today but must have provided stability and stiffness which only a few wealthy amateurs can dream of.
My mounting axes, bearing housings are self reinforcing through box section, assembled 10mm plates. The heavy threaded rods which clamp the flange bearings to each end are heavily tensioned to provide immovable resistance. Multiple cross studs clamp the plates rigidly together and lean on the larger rods for added stiffness. The 20mm thick PA support fork tines are clamped either side of the PA bearing housing with a 16mm through stud for extra stiffness.
Then I dangle the drive motor housings from 10mm thick plate clamped under the same, rigid bearing flanges. So far so good.
Or is it? The flimsy, worm/motor housings are held on by a couple of relatively tiny screws. These screws pass through 6mm box sections of aluminium. Does not compute!! Fail! Must try harder!
The linear "hinge" movement of the worms relative to the wormwheels is minute. What about using rubber bushes bonded into metal tubes like car engine mountings? Adjustable screws can provide the limiting restraints on total worm movement relative to the wheel teeth.
I decided to drill new holes in the motor housings spaced well apart. Then I dropped tiny O-rings over the fixing bolts and sandwiched them between the support plate and the motor housings. The noise from the motors dropped remarkably and there was no more backlash. I can adjust the worm/wheel mesh by tightening the relevant fixing bolts.
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