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Taming the up and over shutter.

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#1 Rusted

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Posted 11 October 2018 - 03:49 AM

Much is made of the problems associated with the imbalance of the up and over shutter during its "wayward" travel.

The heavy shutter has first to be lifted to open.

Then restrained from destroying itself at the back of the dome after its CofG passes over the zenith.

 

However, the shutter could be balanced by two equal counterweights on supporting ropes, cables or chains.

Given the nature of a dome's rotation this might cause the counterweights to drag along the ground.

Obviously this can't be allowed to happen.

 

The answer is to stop the weights from reaching the ground by means of a stop on the cable, chain or rope.

The opposing counterweight then finds itself in full control of the shutter during opening or closure.

While the automatically "stopped" weight is relieved of all duty.

An automatic counterbalance system without the need for human intervention.

 

The stop could be as simple as a screw eye and a knot in the weight supporting rope.

Or as complex as you like in a driven open/close system.

 

The "stop" would obviously cause the supporting cable [chain or rope] to go loose and bunch up above the stop. 

Fortunately, tangles can be safely avoided with a pulley, a Huygenian endless loop and smaller counterweight to maintain tension.

 

The entire shutter can be thought of as a sector of a widely spaced pair of pulleys.

One on each side of the shutter.

A pair is needed because you don't want a rope in the middle of the open observing slit.

Though the "rear" weight [opposite the slit] could use a single rope for simplicity.

 

The following image shows the basic idea.

 

counterbalanced up and over.jpg

 

I claim no originality for this idea which just popped into my head as I worked on my own, bi-parting shutters. smirk.gif


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#2 PETER DREW

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Posted 11 October 2018 - 07:16 AM

I've used a similar arrangement with success in the past. I fitted a pulley either side of the rear of the up and over door. A poly rope was then passed over the pulleys and a standard telescope counterweight attached to each end. A "nose" fitted to the centre of the door rear edge then caught the rope in an "arrestor gear" action raising the weights to control the eventual drop of the door. The raised weights then gave an upward thrust to help lift the door again when closing. At all times the rope was under tension so no rope sagging. A piece of carpet glued to the counterweights prevented scuffing of the surface.
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#3 Rusted

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Posted 12 October 2018 - 06:43 AM

Thank you, Peter.

I'm glad my idea wasn't so crazy.

I thought others might chip before I responded to your post.

 

An up-and-over shutter is arguably preferable when there is snow on the dome.

I hadn't thought of that when I made my decision about having bi-parting doors.

The latter would tend to dump the lot onto the mounting as they were opened.

Though a broom [or squeegee on a long pole] would help to clear the dome if needed.



#4 PETER DREW

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Posted 12 October 2018 - 07:48 AM

Thank you, Peter.
I'm glad my idea wasn't so crazy.
I thought others might chip before I responded to your post.
 
An up-and-over shutter is arguably preferable when there is snow on the dome.
I hadn't thought of that when I made my decision about having bi-parting doors.
The latter would tend to dump the lot onto the mounting as they were opened.
Though a broom [or squeegee on a long pole] would help to clear the dome if needed.

Not had shutter snow loading problems with snow as yet, wind driven powder snow gets through the smallest apertures. Icing of the shutter guide rails is more of a concern.

Edited by PETER DREW, 12 October 2018 - 07:49 AM.



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