Half a croissant, on a plate, with a sign in front of it saying '50c'
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The floor is lava!
  [vote for,

I keep adding things to our playground. Someday it will be quite an attraction.

The things involved in making my latest piece of playground equipment fun already all exist but I don't think they will have ever been put together in quite this fashion.
I am going to build a small realistic looking castle with stacked log rounds spray-foamed together for the children. Fake flickering flame led lights flanking the draw bridge accent the "stonework" as dusk settles and the magic starts.
Inside the castle is a large sand box tabletop with platforms around it increasing in height so that any age of child can play in it.
Above the sandbox hangs a projector rigged to an X-box kinect sensor and some open source software which projects a real-time 3D topographical map onto the changing surfaces of the sand. The prototype part of this is complete now and it's a lot of fun. It will be a lot more fun for the kids on a larger sandbox.

The castle itself will be kept beneath its own shelter to shade it during the daytime. This will allow me to suspend a second projector above the castle.
If I bounce this projection off of a four-sided pyramidal mirror to right angles from the source it will be possible to bounce that split image again off of mirrors hanging from the periphery of the shelter to project the same topography onto a sand-moat surrounding the square castle.

Here's where it gets fun.

Beneath the sand moat I will install air lines snaking back and forth in a radiating pattern outwards from the walls. If the air holes drilled into the air lines are all facing slightly off centre and in leaning in the same direction then, when the air is turned on, the fluidized sand will not only behave as a liquid, it should flow in a continuous artificial current around the entire castle.

The projection will be that of bubbling lava projected onto the ever moving sand.

Log rounds placed within the moat will float on this current of sand as they would on water and the kids will be able to play The Floor Is Lava for real!
The floating log rounds will be above the lava projection height settings and so will look just like green islands floating around in the magma.
Landing on any one island will lock it into place and a child will then need to wait for another log-round to pass them in order to jump for it so as not to fall in as they make their way around.

This next bit will need some experimentation, but if I am right about being able to induce a current in the sand then I might be able to make it climb a slight incline all the way around to waterfall at some point in the stream.

I'll probably add a few inverted head gargoyles who's faces and eyes seem to track you as you walk by them as well for a little added touch.

https://www.faceboo...os/1029134691005165 [2 fries shy of a happy meal, Feb 21 2022]

Portchy https://www.google....29&bih=531&dpr=1.56
[pertinax, Feb 21 2022]

Mathmos https://m.youtube.com/watch?v=C_N7ggu7mvc
underfloor heating, light and fantastic ultra grooviness [xenzag, Feb 27 2022]

Liquid Sand Hot Tub- Fluidized air bed https://www.youtube...watch?v=My4RA5I0FKs
Mark Rober does his over-engineering thing. [Loris, Feb 27 2022]

Blower https://www.buschva...bal/en/products/tyr
Probably overkill, but I'm not sure that there's a "middle ground" between these & leaf blowers... [neutrinos_shadow, Feb 27 2022]


       I like it. Be careful though, you do sink in liquidized sand so don't make it too deep. Plus you turn the air off the kids can all get buried.   

       8th of 7 would say: "Therefore here's a bun." but I'll just say I like it conditioned on it being safe. [+]
doctorremulac3, Feb 21 2022

       It'll only be about four or five inches deep. Just enough to bubble and make log rounds and toy boats float.   

       That's where 8th would have said "Then bun removed". (I'll leave mine)
doctorremulac3, Feb 21 2022

       : ]   

       I would have then made a comment about rigging up his cat litter box with something similar, but with randomly moving laser pointers.   

       Ahh we miss that guy.
doctorremulac3, Feb 21 2022

       True story.   

       I suggest Portchester Castle as a model for this; it has a large, open area where the Roman barracks used to be - for the sand - and a much smaller (but still substantial) Norman keep in one corner, where you could put the audio-visual equipment.
pertinax, Feb 21 2022

       + yay for a lava moat!
xandram, Feb 21 2022

       This sounds delightful. I hope you bake it.
Voice, Feb 21 2022

       //I would have then made a comment about rigging up his cat litter box with something similar, but with randomly moving laser pointers.//   

       Wow 2fries, 8th would have TOTALLY put up "Liquid Sand Cat Box". That's not a maybe, that's an absolute.   

       Wonder of one of us should put it up as a tribute? With a disclaimer "The poster of this idea is only doing this as a tribute the the late, great 8th of 7. No cats were harmed in this HB posting."   

       It's your idea, you want to take it across the finish line?
doctorremulac3, Feb 21 2022

       All yours doc.   

       Okay, how to get past the "No cruelty" clause...
doctorremulac3, Feb 21 2022

       Maybe you pick ones that have terminal illnesses?
RayfordSteele, Feb 21 2022

       Thinking about drilling holes at the water level and adding sulphur hexafluoride so that the kids can make and float tinfoil boats but that's probably overkill.   

       Will there be an age-limit restriction on this playground? I think I'd like to spend a day or six trying this out!   

       Ooh, ooh! Could you rig up a fog machine so the fog would spill down onto the kids and have the projectors make it look like boiling oil cascading over the parapets? I'd bun that for sure! [for 8th]
Canuck, Feb 26 2022

       No age restrictions, but you might have to duck a bit.   

       No boiling oil!   

       Save that shit for the soon to be annual, tricycle-jousting, pond spanning log-walk pillow fight, and the full-contact garbage-can chariot races sir!   

       Yes. You will be expected to switch riders at the mid-point at which point you will become the horse.   

       No boiling oil though. Sorry.   

       Mathmos from Barbarella (link)
xenzag, Feb 27 2022

       //Thinking about drilling holes at the water level and adding sulphur hexafluoride so that the kids can make and float tinfoil boats but that's probably overkill.//   

       All gasses are miscible (that is, mix over time), so it will escape. According to wikipedia it's also an "extremely potent and persistent greenhouse gas".
It's probably not worth it.

       Regarding your sand-floating log rounds, I have some concerns about the stability. Assuming the fluidised depth is low, a child standing on one may get it to 'ground', but maybe it would still roll?
If you paired two logs together maybe that would make them more stable?

       I think you will need quite a sizable flow of air to generate any significant area of fluidity. I did a quick search and found Mark Rober had made a video "Liquid Sand Hot Tub- Fluidized air bed" (linked). Which I've actually seen already. This would probably provide you with useful guidance.
I looked at the build notes he posted in the description and he says a $20, 113lb nitrogen cylinder would supply a sandpit area for about 10 mins. And a small compressor is enough to fluidise a one-foot square area continuously.

       I also don't know how fluidised sand behaves as depth varies. You can't afford to have the depth too high because children are going to fall into it. If it's shallow, though, does it still work? Does it need less air, or more? My intuition (which I don't trust) is that shallow depths might need more, lower pressure air.   

       It may work, but some experimentation would be required. And eye protection.
Loris, Feb 27 2022

       Lots of experimenting. Can't let the kids have 'all' the fun.   

       When I say log rounds I mean maybe ten centimeter thick rounds which would float on their sides like lily pads.
The sand bed won't be much deeper than the rounds are thick.
I have a fairly large compressor but I assume it will deplete after a few minutes before needing to refill. To get around this I had thought to add a random timer to suddenly cut airflow every so often making The Floor Is Lava a bit more like Musical Chair. An added challenge because the floating pad being jumped to might lock into place at any moment.

       [2 fries shy of a happy meal]; you want a blower, not a compressor. (Most) compressors aren't designed for continuous flow, more small volumes at pressure. A (positive displacement) blower gives the flow & pressure together.
neutrinos_shadow, Feb 27 2022

I figured that if a small compressor can continuously fluidize one square foot of sand then a compressor with a much larger holding tank at max psi should work much like a nitrogen tank and give me ten minutes or so of run time between charges.

       What do you suggest? Leaf blowers?   

       Depends what volume flowrate & pressure you need. For a "kids sand pit" size, you might (unfortunately) be getting in to "small industrial" level blowers. There's probably a second- hand market you can tap into for them, though (I know you're good at finding random deals like that...). See linky for a model I'll be installing soon.
neutrinos_shadow, Feb 27 2022


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