Author Topic: String Telescopes  (Read 1201 times)

Duana Beckwith

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String Telescopes
« on: December 24, 2017, 05:49:02 PM »
Anyone make a minimalist dob with alloy or CF and strings in 10" or larger size?
I recall one by Litescopes a few decades back which fit in a bag.



ceicomfeara

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Re: String Telescopes
« Reply #1 on: December 27, 2017, 03:10:25 PM »
I'm planning to make my 20" a string telescope. So far I'm still finishing my 8" (mirror is at OWL for coating). Did you look at Don Peckham's page:http://dbpeckham.com...StringScope.htm I have a build thread for my 8" called Charlie's first scope.

luseatcidood

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Re: String Telescopes
« Reply #2 on: December 29, 2017, 01:46:28 PM »
I have one in the works - a 16" f/4 - it will be a tensegrity style based on the one created by Don Peckham. I have been meaning to start a build thread for quite a while - just haven't gotten to it yet. I have a picture attached of my OTA structure - currently using 1/16" steel cable as a mock-up - the strings themselves will be either BCY450 or UltraCAM bowstring material (I managed to find UltraCAM online - it has been discontinued by the manufacturer).
Several folks here in Portland have built string telescopes - Dan Gray is the original creator; David Nemo built a 20" string telescope and had a build thread here.


Matt Victorin

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Re: String Telescopes
« Reply #3 on: January 01, 2018, 01:51:58 AM »
Quote
tensegrity

I've got your tensegrity right here...


presalacder

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Re: String Telescopes
« Reply #4 on: January 01, 2018, 10:09:56 AM »
Is that a bicycle wheel for the UTA?

Quote

I have one in the works - a 16" f/4 - it will be a tensegrity style based on the one created by Don Peckham. I have been meaning to start a build thread for quite a while - just haven't gotten to it yet. I have a picture attached of my OTA structure - currently using 1/16" steel cable as a mock-up - the strings themselves will be either BCY450 or UltraCAM bowstring material (I managed to find UltraCAM online - it has been discontinued by the manufacturer).
Several folks here in Portland have built string telescopes - Dan Gray is the original creator; David Nemo built a 20" string telescope and had a build thread here.

tensegrity_string.jpg


tioraigenroi

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Re: String Telescopes
« Reply #5 on: January 03, 2018, 08:42:09 PM »
Yes - it is a bicycle wheel - strong, stiff and lightweight!

Jessie Forbes

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Re: String Telescopes
« Reply #6 on: January 11, 2018, 02:37:08 AM »
Help me out here. I'm not seeing how it comes apart? Is it a real pain to set up? Or does it not break down?

exmartata

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Re: String Telescopes
« Reply #7 on: January 12, 2018, 06:54:52 AM »
Yes - it does come apart - and the set-up is minimal.

The strings and the square ring in the center remain attached to the UTA and mirror-box. When collapsed, the UTA sits on top of the mirror box. The 4 poles (at the corners) are the ones that get removed (or put back in). They have 3/8" bolts attached to the bottom end and the top end fits into small tabs of aluminum bolted to the UTA ring. The poles are simply turned one way to tension the strings and the other way to loosen. On the mirror box side - the bolts are screwed into T-nuts that simply sit on the mirror box held by the little pointy tabs on the t-nut inserted into matching holes - this allows the poles to be removed quickly after the strings are loosened, without having to unscrew the poles back out.. (this was idea picked up from Albert Highe's new book on string telescopes).<p class="citation">Quote

Help me out here. I'm not seeing how it comes apart? Is it a real pain to set up? Or does it not break down?
[/quote]

malralilin

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Re: String Telescopes
« Reply #8 on: January 13, 2018, 05:05:12 AM »
Thanks. As you explain it I can see it now.

Marlin Riewer

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Re: String Telescopes
« Reply #9 on: January 16, 2018, 01:19:30 AM »
Is there any chance for collimation issues due to imbalanced tensioning of the strings or improper installation of the poles when this is taken down and put back up?

I am wondering how much weight is saved versus the added complexity in setup if it is worth doing it. I too am build a dob and am interested in truss and string dobs so this is the question I am faced with.

best of luck.

Frank

Chris Jiles

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Re: String Telescopes
« Reply #10 on: January 25, 2018, 05:41:16 PM »
Is a string scope lighter than an all pole truss scope? I'm thinking of converting my 10 monster DOB into something more likely to get used. Right now, I'm disinclined to even move it, much less lug it outside and use it. I've got Highe's book, so I'm hopeful.Michael

Omar Manning

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Re: String Telescopes
« Reply #11 on: January 25, 2018, 08:27:29 PM »
Not really, but generally can be stiffer overall which is why they're popular. You trade the mass of the struts that work in tension for strings that work in tension, and replace the compression struts with heavier fewer ones. It does depend on what you use for strings and more than that what your design goals are. Uhm, you do have design goals, right?

James Holt

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Re: String Telescopes
« Reply #12 on: January 25, 2018, 08:32:54 PM »
Professionals never use strings, always use trusses.

There is a reason.

Flexure.

At an ATM scale it may be possible to build a stiffer string telescope than a poorly executed truss scope, but ultimately a well executed truss will always be stiffer than a similarly well executed string scope.

steviselath

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Re: String Telescopes
« Reply #13 on: January 26, 2018, 01:14:25 AM »
Maybe you're right. I remain optimistic I imagine extremely large telescopes (ELTs) use both tension and compression. I just now found this post hoping to find something to backup my assumption about ELTs. It basically seems like what I've been going for with my 8" build.http://www.cloudynig...ing-scope-r1076

Quote

Professionals never use strings, always use trusses. There is a reason. Flexure. At an ATM scale it may be possible to build a stiffer string telescope than a poorly executed truss scope, but ultimately a well executed truss will always be stiffer than a similarly well executed string scope.


Yung Pryor

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Re: String Telescopes
« Reply #14 on: January 30, 2018, 11:56:29 PM »
Quote
Professionals never use strings, always use trusses.

There is a reason.

Flexure.

At an ATM scale it may be possible to build a stiffer string telescope than a poorly executed truss scope, but ultimately a well executed truss will always be stiffer than a similarly well executed string scope.


When I say "stiffer overall" I mean of course for the same mass. What "professionals" use for large telescopes has nothing to do with that, few "professional" scopes are meant to be light weight, knock down and travel. If you don't use some conditions (such as "same mass" or "some given mass") this comparison is meaningless, as I can ALWAYS build a more massive structure that will exhibit more stiffness (resistance to load deformation) than any given example of ANY design. "Flexure" means something else, simple bending.  Stiffness is what you want when it comes to the primary purpose of any portable scope, affecting its ability to maintain collimation within some arbitrary tolerance.

If this comes across as cranky it's because of the headache I have right now, so I'm not picking on your post.