Building a portable micro planetarium with kids

[Schorhr]

Sorry if this does not really fit into the observatory forum, but I was not sure where to put it.
If necessary, I hope a moderator can move it to the appropriate section.

After I have successfully build the "space-time/gravity simulator" (see http://stargazerslounge.com/topic/216028-theres-a-binary-star-system-in-my-living-room-and-i-lost-my-marbles/)

I planned on building a wooden version of the paper orion box I found on a german site (observatory Recklinghausen).

If viewed through the hole in front, you see the constellation of orion.

When you remove the side lid, you see that the stars are not on a flat canvas, but only look like orion from the front, teaching that space is huge and we are not living under a painted sphere ;-)

So naturally I thought I could build another box for a different constellation, and one thought leads to another... Couldn't I build a small planetarium?

After building the space-time-simulator with cheap pipes, I figured it would not hurt to try.

After sketching a little, I even found a project using these pipes,

http://home.arcor.de/mazo/Planetarium/Planetarium.htm

I have to keep it portable and simpler though. But it helped avoid a few obstacles from the start,  as it contained a lot of advice and trial-and-error documentation.

To further reduce the cost I decided to use larger pipe instead of clip connectors, which would also be fatal if they get loose while children are inside the dome :-)

After my animation class and with the help of one of the students I managed to set up the first test dome, using thread instead of zip ties for now.

The space walnut :-)

With more rods and zip ties it will actually be more rigid then I first thought.

One thing that still troubles me is the fabric to cover the dome.

It has to block the light and the surface has to double as projection screen.

I sid not know even raw fabric would be so expensive :-)

So what to use?

The german project darkens the room and uses paper.

I have considered Paper covered with tinfoil, but that would not last long. One of the early ideas where rescue blanket or other foil spray painted with matte white paint, but the spray paint costs about 5€ for a little over 2 square meter coverage, for 20-30qm dome surface that would be too much.

As I volunteer at a school, pretty much everything has to be low budget.

The most promising budget idea right now  is PU/Felt drop cloth / painter cover fleece.

http://www.ebay.de/itm/Malervlies-Abdeckvlies-Schutzvlies-Renovierung-Vlies-PE-Folie-50m-100m-150m-/190965426262?pt=DE_Haus_Garten_Heimwerker_Bodenbel%C3%A4ge&var=&hash=item2c766d2856

When moving to our apartment, we used it to protect the flooring while painting, removing old wallpaper and so on, The thicker 200g/sqm stuff seems to block out enough light, too.

I recently discovered it is being sold as white fabric, so this might work!

http://www.ebay.de/itm/1-m-x-50-m-Abdeckvlies-weis-50m-220gr-mit-PE-Schicht-Malervlies-Schutzvlies-/261491184453?pt=Malerutensilien_1&hash=item3ce216d345

I even found a brand that is pure white, without the typical spots and pieces of other colored fabric.

While the grey-black sheets start around 0.30-0.50€/0.25-0.40€ per square meter, the white variant costs either 1€/0.80£ and up, or is available in larger quantities only.

If anyone knows a cheap source within the EU, please let me know!

Another issue is the projection.

The cheaper toy projectors seem to be rubbish, even the Sega one seems not to be suited for a small dome.

A lot of DIY projects use a sphere around a bright, small lamp, projecting stars via different sized holes.

Simple enough, there are even foldable star globes to print for free, which I could print on cardboard.

Of course using a projector and a mirror sphere (park deck mirror, large Christmas ornament) and Stellarium would be much nicer, even though the star projection would not be as sharp, being able to show nebulae, animations and such would be great..

Well, two days ago I got lucky:

I got this beauty from a projector shop specialized on refurbished and used projectors.

It was sold for 11€/9£, sold as defective... But other then the lamp being way over the estimated life, it seems to work!

Even if I have to exchange the lamp with a tinker solution that does not get as bright, it would be a great buy for the project. The tinker gods have heard my calls :-)

Well, this is all I got so far. I did post in a German message-board and a portable planetarium yahoo goup, but since this forum is more active, I hope some others have attempted building such a dome, perhaps teachers or parents :-)

I would like to exchange ideas, perhaps some have experience they would share, so I can avoid problems or get new ideas.

I did find a few things in blogs and on youtube, but either too sophisticated or the projects died down.

The cardboard domes seem very popular, but I think that solution would not be great for long term use and outdoors, as the cardboard could get wet.

So...

Any ideas for a projection surface under 1€ per square meter?

Experience using projectors?

:-)

[Gina]

Very interesting idea   I'm afraid I don't know anything that would help but I wish you the best of luck in finding an affordable solution

[Schorhr]

Hello Gina,

thanks :-)

I am sure I can solve the issues somehow... As usual the project takes longer then expected, but it has been fun working on it.

[saac]

Schorhr,  this is brilliant, your ingenuity is fantastic.  Most portable planetarium cost around 10 of thousands and are well outside the budget of schools.   I guess the really tricky part is the projector technology.  Have you thought about modifying the lens of the projector to project on the dome.  I remember reading of a similar diy planetarium where a fish eye lens was mounted to the projector - a google search may yield something, I'll take a look to see if I can find the articles again.  I would love to get something like this to use in my classroom - we would never be out of it!  Good luck, I'm following intently.

Jim

[Schorhr]

Hello Jim,

thanks!

Yes, my research brought up fish eye lenses too, but for short distance mirror spheres (park deck security mirrors, silver Christmas ornaments) seem to be a inexpensive solution :-)

I may have a fisheye lens I can borrow, but I hope the mirror thing works.

Also the pinhole projector can be done for a few bucks, printer, cardboard and a bright lamp with small tungsten filament... and lots of time to punch holes in different sizes :-)

So basically like these

http://www.ncsm.city.nagoya.jp/cgi-bin/en/exhibition_guide/exhibit.cgi?id=A531&key=P&keyword=planetarium

http://www.ebay.com/itm/Otona-no-Kagaku-New-Planetarium-Kit-Real-Star-Gakken-Mook-From-Japan-/310941294781?pt=Educational_Toys_US&hash=item48658ba0bd

http://analyzer.depaul.edu/paperplate/All-Sky%20Projectors.htm

So either

http://www.atlasoftheuniverse.com/skyglobe.html
http://www-personal.umich.edu/~jimw/Skyglobe/

or even http://www.thingiverse.com/thing:36413 could work.

Though I would like it to be easily duplicable for others, so I shall punch a thousand holes until my fingers are sore...

I even thought of creating a nail-board to punch holes in several of these and give them to students for their rooms.

If you find any relevant articles please let me know :-) One one hand there is a lot of articles on DIY planetarium, but either not documented well, too simple, or expensive... I am trying to find a way between low budget, simplicity and functionality ;-)

Even if I had not acquired a cheap projector, I would probably have build one out of a used TFT display or the 10£/13€ china panels, a bunch of halogen Lamps and fresnel lenses.

If I can source the white painter's felt tarp for an affordable price in smaller quantities then wholesale (my major concern at the moment, who would have thought cheap textile/fabric is hard to get), I could build the whole thing including pin hole projector for around 30€/25£ or so. At that price tag, there's no excuse for not building one ;-)

[astronymonkey]

Having dabbled with planatriums a few times I thought Id add my thoughts...

For the dome one of the key issues is a decent level of reflectivity as this will reduce the level of power needed from the projector. In this case I would go for white fabric and wouldnt mess on too much with silvered surfaces as they will tend to shed particles unless well made. Another issue is pinholes in the fabric and for a budget system a darkended room is essention in order to minimise the effect of pinholes and slightly see through fabrics. For the fabric one of the options is the fabric used for blackout curtain linings as this is relatively cheap and can oflen be picked up from charity shops and is easily sewn together. You would need to make sure the pieces are cut correctly in order to make a hemispherical shape but some basic maths and a bit of dress makers chalk is all you need. If you want to go self supporting then foamboard may be an option http://www.londongraphics.co.uk/products/Graphic-Supplies/Board-Card-Paper-Film/Foamboard-Polyboard/Economy-Foamboard-5mm-Thick/UNWF5000_RED-BOX-Foamboard-White-A0-5mm but this will put the costs up.

For the projector I think a mirror/projector system may be too complex although is a neat solution but the spread of the beam can be an issue and the power needed can be quite high once bounced off the sperical mirror. You mention making a globe and this would be my preferred route but the trick isnt to make it in card , instead you get the template printed in negative onto photographic film, this gives the sky a black finish with clear holes for the stars but gives a better definition than pricking holes and by making the dots vary in size depending on their magnitude. Its also a lot faster.

The bulb for the projector is also something to consider as this needs to be a point source of light and small filament bulbs end up being projected as small lines like a pinhole camera. I would think an led system could work well and would run cool aswell.

Finally, I know one of the issues we had to deal with was making sure that fire safety was thought of. So be careful with electrics, hot bulbs and flammability of fabrics. It might also be an idea to have the dome elevated on legs so people just duck under the sides and this also means that views heads are below the horizon and dont cast shados on the sky.

hope this helps,

[Schorhr]

Hello,

thank you for your very informative post!

What kind/size of planetarium have you build or worked on?

# Fabric

It is allways a bit difficult for me finding products I do not know or if I am unable to the apropreate German translation for it. So please excuse me if I looked up the wrong material :-)

Blackout curtain lining, if I looked at the right thing. costs about 5-8£ per square meter?

Or do you have a link to a shop or something?

That is much cheaper then "black out" type projector curtain, I will look into it. :-)

But I am afraif that for the non-budget dome it will be too costly, as it would cost about 100£ for the 30sqm. :-(

As for my current plan:

I now found a better deal on the 220g/m^2 felt painter's tarp, it looks like this;

- http://www.msh-malerzubehoer.de/SONDERAKTION-Abdeckvlies-Velour-weiss-1-m-x-25-m-91422.html

- http://baucompany24.shopgate.com/item/3134303139

- http://www.lasala.ch/product_info.php?info=p1145_abdeckvlies-weiss.html

- http://www.stickel-bautechnik.de/epages/61460863.mobile/?ObjectPath=/Shops/61460863/Products/12.3463&Locale=de_AT

Sorry. Hard to find a goof picture of the thickness and (lack of) transparency of the material. The grey stuff is more common ( http://www.alfa-direkt.de/alfa-abdeckvlies-anti-rutsch-beschichtet.html ).

There are variants with random enclosures and colors, such as http://www.protect-cover.de/portfolio-produkt%20dampfsperre.html (white is at the bottom) so I have to be careful which I buy.

0,50€/0.40£ per square meter, it is by no means perfect for projection but at least the grey variant does block the light well. And even if the thick while felt does not, I can just cover one side with rescue blanket or tinfoil-ish material.

I have some of the gray stuff from when moving to our current appartment and it should be rigid enough. It is thick and the ptfe plastic backside makes it relatively tear-proof, though I am not so sure about sewing or attaching Velcro to it... Thus a clamp-connection with a long piece of wood plus screws and wing nuts might work.

#Shape

As for getting the right shape, I have found a "orange peel program" that will calculate the pattern :-) I think this would be the easiest. Perhaps printing it on paper and giving it a test-run before working with the white fabric.

#Foam board

Interesting, and not as expensive as the stuff I have seen at my local hardware store! I got to check if I can find that stuff here.

Perhaps if I ever get the chance to build a more stationary one I use that :-)

#Mirror

Yes, I just chose to try this approach as it is inexpensive and I have some materials here to try.

The main problem will allways be the 200 ANSI Lumen projector covering over 20 square meter of surface... If the bulb lasts long enough, as a possible diy replacement would be even less bright.

Not to mention xga resolution spread all over the large area! :-)

So I will defiantly build a pinhole projector, too.

I even seen combinations of those methods; The stars beeing projected by pinholes, a computer projector just projecting the color nebulae image.

#pinhole projector using film

Now this seems like a very interesting attempt!

Just on 35mm negatives you mean?

I have thought about using (multiple layers) of printable transparencies sheets, but I thought it would not block the light well enough.

#pinholes

For a cardboard pinhole sphere I was planning on using four or five different needle sizes.

But I love the idea about fim negatives sheets.

#bulb

I allready have ordered a inexpensvie, small thread light bulb, as it was used in the German project I mentioned.

I thought about LEDs too (also because of the cooler temperature), but are there single LED bright enough? Panels would not create a pinpoint light source...

Or should I make different sections of the sky with a 3w LED each?

Of course then I could use single negative or projector slides, Fresnel lenses and halogen/led spot as very cheap light source.

I also thought of this but instead of slides/negatives using the 10£ car displays sold on eBay.

#Dome elevation

Yes, good idea.

I would put the dome on school chairs or tables perhaps, and/or let the kids sit on one side :-)

I know the project seems not very thought through yet, but it is a nice experiment and I am sure something nice will emerge out of the many ideas and sketches. I do not want to create a second dome planetarium for our city. Just something the kids will enjoy :-)

Thanks again for all the ideas and suggestions.

[astronymonkey]

Hi Marcus.

Im no expert but I am currently involved in a planetarium we run as a not for profit charity and are in the process of taking over  the facility to prevent it from council closure -  although members of the local Astronomical Societies have helped as volunteers for many years and played a signifincant role in builing the facilty.

At present we have a 7 metre fixed dome hemispherical screen,  which is tilted a few degrees to make viewing easier. The dome is loosly suspended in the roof space which  is air sealed as much as possible and powerful extractor fans draw out the air causing the dome to be sucked up into the ceiling space which pulls it taught. Its a negative pressure system which is basically a reverse of the inflatable systems you can get

The dome is held loosely by tethers to the ceiling timbers and we have a noraml fan which is on all the time to keep the roof space dry and we have a show fan which moves a greater volume of air so can cause sufficient vaccum to pull the dome.

As far as Im aware our fabric dome is made from similar maerial to blackout curtains ( ie the linings which are often used behind the curtain fabric to give a degree of insulation and to prevent sunlight shining through) but Id have to check if it was coated in any way.

For a projector we use an old Goto system but we are looking to upgrade to a spitz 1024 projector before the end of the year.

We aim to combine the optomechanical projector with a DLP projector as well but the DLP systems arnt as good as rendering stars as an optmech system which is why many systems use a combination of both.

Although this is a fixed theatre I have also helped run some shows in the past in an inflatable dome which used a DIY projector. This used the film based projector but this was printed onto large 8x10 film sheets by a professional lab. This meant that the whole sky could be printed on 3 sheets attached together and rolled into a cylider with a round piece of film print covering the top. I believe the original system used a pinhole method but this couldnt get pin holes small enough to render small stars. 

Id be really interested to see how your project develops as doing it on a budget is difficult due to some of the complexities of the dome and projector but Im sure you will find a way of making it work.

If you want to really spend some money, go for the Zeiss Velvet DLP system in its full 8 projector configuration, only 250,000 euros .......... per projector.

Cheers

[Schorhr]

Hi, sounds very interesting :-)

Sadly I can not install it permanently nor afford better equipment, but the school has been very supporting for my projects so far.

I looked into a DIY dome solution but it was more cost intensive, complicated to build and to get light-tight... So I decided on a tent solution :-)

A 7m dome is another league, awesomo.

As for black out fabric 5€/sqm was the cheapest I could find atm, so at least 100€.

Even the combination of tarp plus non-black-out-canvas gets quite expensive. Oh well...

For the first build I am sure the white felt tarp will work, though I can only get it in quadruple the quantity I need.

I will look into the photo paper/foil solution, I hope I can find a company that does that.

Many pinhole projectors seem to use a Dodecahedron, I suppose it is less work then a sphere and less distorted then a cylinder?

I have seen cylindrical projects on-line as well, it would be a lot easier to build :-)

I dislike DLP projectors due to the "rainbow" effect, some seem to notice it less then others.

The planetarium here uses(used) similar set ups, lots of projectors and speakers behind the dome, awesome technology.

I also just returned from the last of our hardware stores here, no white felt tarp either.

Oh well, it all does not have to be perfect, as long as it fun and somewhat works :-)

[Uplooker]

Hi Marcus,

Just read this thread. I am awe struck at your determination, ingenuity, perseverence and striving to bring astronomy to the uninitiated. All I can say is well done and good luck in your achieving your objectives.

Ian

[Schorhr]

Thanks Ian :-)

Now, if only the kids had as much fun as I with these projects...

[astronymonkey]

http://www.ips-planetarium.org/?page=pdg

hi marcus,

the dodecahedron globe is a resonable compromise for a globe and was used in the original spitz a1 projectors from the 1950s and were commonly sold to schools and colleges. I even think albert Einstein had some involvement I the development of the shape after advising spitz on which shape to use.

the cylinder system we used to use was actually printed on photographic film, not photographic paper, so acted like a big cylindrical photographic slide and worked ok. In your system maybe a childrens planetarium toy projector could work or at least give some ideas of what could be tried.

Ive attached the link to the planetarium development guide on the international planetaria website which might help.

cheers

[Schorhr]

Thanks, I will read through that :-)

Interesting bit of history, I will check that out, I wonder if there is a source about that, I love details like that :-)

I have read a lot of reviews of toy projectors, most reviews where bad, some are just ceiling projectors, other not bright enough.

The sega had decent reviews and a german company sold a cheap no name lablel version of it, but it is not available at the moment.

Also Gakken had one to build but at that price tag I would go for my own.

Yeah, I understood that it was the transparent negative, I will try to find a company who does that, there might even be a local company that does it.

Or I attach a dremel tool to my reprap and let technology do it :-)

[Schorhr]

I just did a search, a lot of companies offering slides from digital media, some sheet film size 5x4in, but 39€ ea. will be more then the whole dome will cost :-)

Perhaps I will try inkjet transparencies, and multiple layers. 16 cent per letter sized sheet... But probably the quality will suck.

No laser printer at home, either.

I guess I could project the whole sky with a single, small slide, if I had a very wide angle lens... Probably going to browse Aliexpress and ebay :-) So something like http://www.ips-planetarium.org/?sfxslideproj .

This could then be completed with the same setup but a

http://www.ebay.co.uk/itm/3-5-TFT-LCD-Monitor-Display-Hintergrundbeleuchtung-fur-Reverse-Ruckfahrkamera-/111326213559?pt=Auto_TFT_Monitore&hash=item19eb8f35b7

http://www.ebay.co.uk/itm/3-5-TFT-LCD-Display-Car-Reverse-RearView-Monitor-for-DVD-VCR-Backup-Camera-BE0D-/131166549701?pt=AU_Car_Parts_Accessories&hash=item1e8a22b6c5

http://www.ebay.co.uk/itm/4-3-Zoll-LCD-TFT-DISPLAY-PKW-Auto-Monitor-fur-Ruckfahrkamera-DVD-VCR-CCTV-/111364764821?pt=Auto_TFT_Monitore&hash=item19eddb7495

But not as main projector... With 320x240 a pixel would be up to 10cm wide in the dome :-) But perhaps nice to throw some color or faint fuzzies in there... fuzzy indeed :-)

Horrible but I love these tinker solutions for a couple of bucks.

[Schorhr]

Sorry, just me again.

A lot of sites link to http://www.cccoe.net/stars/ but it has been ofdline since I started my research.

Any one here knows if it will be back up? Google cachr and image search only goes so far, as most materials and images are lost this way.

[Schorhr]

Hi :-)

Regarding the hole projection:I received inkjet printable transparency sheets today.

As expected, one does not block the light completely where black areas are printed.

Two layers will do a sufficient job.

It might not be as high-definition as negative film would be, but a letter size / A4 sheet costs 18 Cent, while a digital print service negative film would cost twenty times as much for a smaller format :-)

I did not find another light point source, but I have yet to try (and receive) the mag lite mini xeon.

I will receive some white painter's tarp soon as well.

Regarding the digital projector:

I still have not found a spherical mirror >50€. There is one for 40€ but it is a bit small and still costs more then the other materials combined :-)

http://www.ebay.co.uk/itm/Gewolbter-Acrylspiegel-90-Sicherheitsspiegel-Safety-Mirror-Uberwachungs-Spiegel-/261058448004?pt=DE_Haus_Garten_Heimwerker_Sicherheitstechnik&hash=item3cc84bca84

Also the minimum distance is close to 80cm, the minimum image diagonal around 49cm...

I have seen inexpensive light bulbs that are mirror coated, such as http://www.ebay.de/itm/PAULMANN-875-18-DECO-SET-ESL-GLOBE-100-GLAS-KOPFSPIEGEL-10W-SILBER-87518-/301091202327?pt=DE_Möbel_Wohnen_Leuchtmittel&hash=item461a6f2517 -I looked at a smaller one I found at the hardware store, except for the top it seems usable, but of course this may vary from type to type-

but only in 10cm and as I understand the image on the sphere must be focused, so I will need at least a 50cm sphere?

So http://www.ebay.de/itm/Kassenspiegel-Sicherheitsspiegel-konvex-30-Panoramaspiegel-Uberwachungsspiegel-/310944887084?pt=DE_Haus_Garten_Heimwerker_Sicherheitstechnik&hash=item4865c2712c would not work...

Edit: Perhaps http://www.ebay.de/itm/Runder-konvexer-Spiegel-42-cm-Kalotte-Kalotten-Glas-/370920453709?pt=DE_M%C3%B6bel_Wohnen_Dekoration_Spiegel&hash=item565c94f64d ?

I would really like a low budget solution for this part..

Regarding the star sphere:

Does anyone know software to print a star map as dodecahedron segments?

Perhaps a simple way? Cartes du ceil plugin?

Thanks :-)

[saac]

Marcus,

Please keep posting this is fascinating.  Don't be put off by the lack of other inputs - it's such a specialist topic but I guarantee folk are reading intently and want this to succeed.  The research is often the hardest and longest part as I'm sure you know.  Good luck.

Jim

[Gina]

Absolutely agree   Very interesting

[Schorhr]

Thanks to both of you, I was afraid I was boring some here to death ;-)

The white painter's tarp - or what ever it is called in English - arrived.

The good news: It is a pure white, smooth surface. It will probably work for a simple projection.

It is not transparent either, but unfortunately it is translucent, compared to the gray tarp.

So what to do? Tinfoil would work, but rips easily. Cheap rescue blanket only works with two or more layers. A second layer Gray tarp would increase cost and weight.

The Xenon Mini Maglite 2-Cell AA bulbs arived, tiny, bright, but could be brighter. They are indeed small and make an excelent point light source, even slides and color print on the inkjet transparencies reach focus on the wall, amazing - without any optics!

I guess I have to wait for the dome to finish to see if the bulbs are bright enough, perhaps someone can name a bettter bulb?

A larger 30w halogen bulb is MUCH brighter but the filament is perhaps 4mm long, already resulting in a blurry image.

The other alternative is using credit card sized fresnel magnifying lenses (for reading), they make a superb cheap no-budget projector, some distortion of course.

I still was unable to source a spherical mirror segment for a lower price.

The inkjet transparencies star sphere will work, but one layer does not block the light where printed black, two layers dim the light too much as the transparencies are not completely clear due to the coating for inkjet printing.

I would expect that laser printed or copy machine transparencies would work much better, but I currently have no access to one, and in the copy shop the prices are insane.

In other news, http://blog.pixelgiraffe.com/wp-content/uploads/2014/06/DSC_0740.jpg

;-)

[saac]

Marcus,

Don't know if this stuff would be any good - it's styled Blackout Lining - designed for backing curtains and blinds to make them light fast.  I wonder how much light it blocks on its own.  I wonder if they provide samples.  Dunelm are a fairly reliable and  well known high street store in the UK.

Jim

[Schorhr]

Hello Jim,

I've tried finding a cheap source, but for 20-30 square meters it is just too expensive... As usual, looking for the low budget solution :-) Perhaps Tinfoil+Tape to prevent it from tearing... who knows.