Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Help needded for flexible planetarium dome build

  • Please log in to reply
14 replies to this topic

#1 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 13 September 2019 - 07:04 PM

Hi folks,

 

Cloudynights doesn't have a planetarium forum, so I'm not quite sure where to post this. Bu this is where the builders gather, so it seems like the best fit.

 

I put up a post over at the Observatory Central website, which has several different forums related to planetariums. But it does not get the traffic and views that CN does, and I haven't gotten any responses. It's been up for less than 24 hours, so I may well get some replies, but I figured it wouldn't hurt to post here, too. Rather than r-write everything I wrote there, I'll just paste in what I posted there. If anyone has any ideas, leads, critiques, or whatever, I'd be grateful for them.

 

"I was given a Spitz A4 projector by someone who has posted here. He had tried to get it up in a public dome but couldn't find a way, so offered it anyone who thought they might be able to. I convinced him that I would give it my best, so he gave it to me, with the understanding that I would give it back if things didn't work out for me, either. In my local school district, we recently got a referendum approved to build a new performing arts center (PAC), and our superintendent loves the idea of making a planetarium a part of it, especially since I'll provide the projector.

 

"Here's the issue: we will (almost certainly) not have a dedicated, permanent space for the dome. The hope is to find a way to make a foldable, 24-foot dome that can be raised up into the 'flies' above the stage. I see it as a fabric hemisphere with a steel skeleton made with -- possibly -- electrical conduit. The fabric material does not need to be completely opaque, since the stage can be made completely dark be simply turning off the theater lights. So the weight of the dome can be kept to a minimum, meaning the steel framing does not need to be super heavy-duty. I see the frame being on the outside, made up of about 18 to 24 ribs, and these ribs will slide through sleeves (just once, when we first assemble the thing) on the outside of the dome. When not in use, the dome should open (with a zipper? Velcro?) and the ribs can then be rolled together to flatten the 'tent' of the dome. It would not need to fold up to the smallest size possible; just enough to be flat enough to raise up on a couple of cables attached somehow to one or more of the ribs. We will have motors that will be able to lift several hundred pounds, so I think this would be easily doable.

 

"When the folded dome is lowered from the flies, I see us opening it up and locking the tightness of the dome by lowering braces that fit between the bottoms of the ribs, and then supporting it on its bottom edge with several (4? 6? 8?) posts about four feet tall, which we will install into some kind of holders in the stage floor. Folks will ether sit on the floor, or we will have chairs that can be set up (we have plenty of those on wheels). We'll also need a way to move the projector on some kind of wheeled base from a storage closet on an edge of the stage. I want to find a way to make this as simple and quick to do as possible, so the planetarium can be set up in a reasonable time, for use by students and the public. I live one block from the school, so they'll have someone ready to help.

 

"I've talked this over with some others who think it can be made to work, and I think I have the skills to do much of it, along with help from the shop teachers at the high school. But the one thing I have no skill set for is the making of the dome. What size and shape to make each of the sections of the dome; how best to sew them together; how to make the ribs come together at the top (I'm imagining a small wheel with all the ribs having rings on the ends; like a giant, round shower curtain.) I'm hoping folks here might be able to point me toward sources/ideas, or even to someone who has, or who could, do it. I've been told (but not gotten a guarantee) that the school district could find some funding for the making of it. I'm on the school board, so I might have some influence on that (but again, cannot guarantee it yet). If I had some solid leads, I could present the idea for consideration.

 

"Again, the projector was originally housed in, and is set up to be used in, a 24-foot dome.

 

"I could write a bunch more right now, such as how I own and use a Starlab 16-foot planetarium. And about talking with John Hare from Ash Enterprises about this project, since he services the A3p projectors at two schools (one high school and one university) nearby. But I'll wait to say much more while I wait to see if anyone here can help. The ground-breaking for the new PAC is going to be some time around Thanksgiving this year, with the construction lasting about twelve months. The planetarium project does not to be done as part of the initial building of the PAC, but I think it would help to keep the idea moving forward if it was at least well under way during that time.

I only post here every few years, and always have gotten great advice. Thanks in advance for any ideas!"



#2 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 13 September 2019 - 07:12 PM

Here's a photo that shows what I got. Not my specific projector, but one just like it. I didn't get a desk, but I did get the control panels shown on the desk. When this thing was new in the early 1970s, it cost the price of a modest house. There are still lots of them in use today, including two one at a college an hour and a half from me. They can be updated with LEDs (cooler, lower-power, and much longer-lasting) instead of halogen lights.

 

Most planetariums that could afford it have updated to digital projectors. While digital has some definite advantages (time-travel, better video possibilities, space travel), I think the stars shown by an analog machine look more realistic, and the background sky is black.


  • brave_ulysses likes this

#3 Myk Rian

Myk Rian

    Viking 1

  • *****
  • Posts: 885
  • Joined: 11 Aug 2017
  • Loc: Hartland, Michigan

Posted 14 September 2019 - 07:17 AM

I'm trying to imagine a removable planetarium on a stage, and have come up with a blank. Good luck.

Myk

#4 Ed Jones

Ed Jones

    Soyuz

  • *****
  • Posts: 3839
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 14 September 2019 - 08:36 AM

You need something like this



#5 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 14 September 2019 - 11:06 AM

Thanks for the tip, but I already have something like that, though much older. (That's my actual dome, on a page at my website.) But there are two issues with both of them. First, how to get the projector inside. I suppose they could be used by attaching sleeves and metal rods, as in my idea (though that would be very difficult as they are made out of special opaque material). That would allow them to be lowered over the projector (they do not have complete floors underneath). The projector is too big to fit through the portals meant for entry.

 

But the other issue is that they are too small. They are both about 16 feet across, and the A4 is not designed to use on that small a diameter.

 

Sorry for not mentioning that I'd already considered this!

 

I've looked online for plans or calculators that show how to design the panels needed for a fabric dome but have had no luck. If no one else knows of someone who might be able to make this for us, we might consider making it ourselves if we had the pattern.



#6 Ed Jones

Ed Jones

    Soyuz

  • *****
  • Posts: 3839
  • Joined: 06 Apr 2004
  • Loc: Sin-sin-atti

Posted 14 September 2019 - 11:42 AM

They list a 7 meter dome.



#7 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 14 September 2019 - 12:53 PM

Thanks, Ed! I'll look into that, but still see an issue with attaching it to some kind of framework so that it could be lowered onto the projector. And not only the projector, but the station the planetarian will work from. I will check more carefully into what the dome is made from; maybe they can send me a sample.

 

But I'd sure like to hear other ideas, too.



#8 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 14 September 2019 - 01:07 PM

Looking again at the site Ed Jones pointed me to, I see that the manufacturer states that they'll make custom orders. I'm going to write to them with my ideas and see what they say.

 

It was a bit odd to read that they have 'two years' of experience, and they put that like it is supposed to be a claim to instill confidence. Still, if they can do what I need, then that's fine. I ordered a custom-made (sort of; it was put together from components) lifting column from a small Chinese company a year or so ago, and after lots of cross-language clarifications (no one's fault, just the reality), I got a very satisfactory product for a very reasonable price.

 

But this will be taking a risk with an unknown producer halfway around the world. I'll have to convince others to go along with spending funds. So other ideas would still be really helpful, if only to have some other possibilities to compare this one to. I've done lots of searching myself, but drawn a blank. I had not found Ed's link, though, so either it's fairly recent (it's been a while since I looked), or I just missed some search parameters.



#9 jtsenghas

jtsenghas

    Skylab

  • *****
  • Posts: 4303
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 15 September 2019 - 09:33 PM

I love the concept and can see why something without a floor is really required in your (likely) unique situation. I also see that your setup is a bit large as compared to most portable setups.

 

I can see how structurally a collapsing ribbed structure poses some problems in going relatively flat, and also that the projector likely needs a fairly elevated horizon.

 

I'm wondering if perhaps the external semicircular ribs should be arranged more in a clamshell arrangement, attached with pivots to a small hub in each side. (think of the longitude lines of a hemisphere of a globe of the world turned sideways).

 

I'm imagining rolling out sections of wall first, including one that has a door in it and latching them together. Then, the collapsed dome is lowered onto it and fastened to one half of the cylindrical shell of the wall. Finally, the structure is opened like clamshell Observatory closing. As soon as the first rib is raised significantly, possibly with a pusher pole, a rope pulling from the opposite side could pull the rest up and over. This would be a bit like extending the hood over an old fashioned baby buggy.

 

Structurally, this could be very simple. 



#10 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 16 September 2019 - 12:03 AM

jtsenghas: I think I can visualize what you are describing, yet I may be missing something. But I don't think we will need walls. The theater will have the capability to go to complete darkness (other than some distant, dim, exit signs). So as long as the bottom edge of the dome can be made stiff, than it can be supported by several vertical posts.

 

I've been away since I last posted here, and I'll think about what you've written.



#11 jtsenghas

jtsenghas

    Skylab

  • *****
  • Posts: 4303
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 16 September 2019 - 05:23 AM

Okay, several discrete posts work well too, and promote air circulation among the viewers. It's just that the hub regions will have to be eirher anchored or set on the floor while the structure is opened. I'm thinking of a few ways to handle the pivots. I'll try to make a sketch later today. My last post was a late night musing and I'm off to work now.

 

Edit - Actually I can think of a way that more elegantly manages this for deployment and storage. Both sides can fold up to the center, towards a meridian that passes through zenith. This means that for north and south hubs, lifting lines attached to a few east and west horizon hoops would automatically collapse this upon rising and would lower it without side loads opening it automatically. You would just need a person at each the north and south end  to help place it as it is slowly lowered.

 

Yes! I can see how to manage the potential spinning too, going up or down. Stay tuned. 


Edited by jtsenghas, 16 September 2019 - 05:41 AM.


#12 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 16 September 2019 - 08:28 PM

Oh, you've got me staying tuned now! Thanks! grin.gif



#13 jtsenghas

jtsenghas

    Skylab

  • *****
  • Posts: 4303
  • Joined: 14 Sep 2014
  • Loc: The flatlands of Northwest Ohio 41.11N --Bloomdale

Posted 16 September 2019 - 08:47 PM

I am sorry not to have more for you yet. I just had an extraordinarily long day at work today. It was a Murphy's Law Monday at the factory. 

 

I'll try to make a couple of quick sketches tomorrow of the framework I propose. The most difficult part of the project would be the fabric work, I concede that. I don't see how most possible designs would be much simpler regarding the fabric work than my idea, however. You have several advantages in your situation as compared to most collapsible planetariums. The fabric can be lightweight since it may be translucent, and having a large overhead space to hoist it to means semicircular hoops may remain intact. 



#14 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 17 September 2019 - 12:29 AM

I've seen the kind of work you've done, so I'm really looking forward to what you have in mind. But I'm not in a big hurry. I know what long days are like. Thanks for the thought and the help!


Edited by PaulEK, 17 September 2019 - 12:29 AM.


#15 PaulEK

PaulEK

    Surveyor 1

  • *****
  • topic starter
  • Posts: 1791
  • Joined: 25 May 2008
  • Loc: Wisconsin

Posted 17 September 2019 - 08:25 PM

Well, I just noticed my misspelling of 'needed' in the title of this post. As an English major, I'm a bit chagrined.

 

jtsenghas: I realized earlier today that, if I understand your idea correctly (which is only somewhat likely), your flattened dome will be a semi-circle, whereas the idea I described is a quarter of a circle. Won't this mean that, for a dome 24 feet in diameter, your flattened one will be twelve feet from top to bottom, while mine, tilted sideways, would be significantly less? If the little sketch I just made is right, mine would be about 17 feet long and about four feet 'high' when folded up and tilted sideways.

 

Our theater is being built without 'full flies', meaning there will be a limit to how much height we will have to store things up there. I don't know offhand what that height is, but I can find out.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics