Someone suggested I cosplay Onion-San from Undertale and I concluded it was an utterly ridiculous idea: The outfit would be the largest and crudest thing ever seen at my local convention.
So naturally I accepted the suggestion.
I think that the best way to go about this would be to make some kind of inflatable octopus costume..
But the problem is that to not have the tentacles drag on the ground I would probably need some air escaping, and to have air escaping I'd need to be carrying a battery and an air pump, which sounds impractical.
How realistic is this idea?
to not have the tentacles drag on the ground I would probably need some air escaping, and to have air escaping I'd need to be carrying a battery and an air pump
https://www.youtube.com/watch?v=rHXvMcLrLSY
But seriously, how big are we talking here? There are a handful of electric-blower inflatable costumes out there already. Here's an example of a blower that runs on AAs: http://www.yardinflatables.com/Replacement-Fan-for-Inflatable-Costume_p_2178.html
And the sort of costumes it goes with: http://www.gemmy.com/Airblown_Inflatables_Costumes_s/1848.htm
>>983954
I'm willing to invest in a good pump since I've been looking at making a furnace, though I don't know how long that would last if I used the biggest battery practical to carry (A car battery for example if that can be somehow used for a pump).
Size of the costume?
As big as is reasonable, it's a fairly large character. Definitely bigger than any of the costumes in that link.
>>983955
>I'm willing to invest in a good pump since I've been looking at making a furnace
I'm not sure what sort of pumping demands a furnace requires, but these inflatables operate at very low pressure and high volumetric flow rates. May or may not be compatible with your furnace.
>I don't know how long that would last if I used the biggest battery practical to carry (A car battery for example if that can be somehow used for a pump).
Alright, well let's see:
http://www.yardinflatables.com/Gemmy-Replacement-15a-Fan-With-12v15a-Adapter_p_1867.html
At 12v and 1.5a, you could run it off a 15 AH lead acid battery for 10 hours straight; such a battery would weigh about 13 pounds. Alternatively, an equivalent capacity lithium pack would weigh about 5 pounds.
Now, the inflatables this pump is designed to work with don't have external air jets like you're describing (that is what you're describing, correct?). Implementing jets would be a pretty significant risk, since you can't really know how well it'll work until you try it, and once you do try it, patching the jets up again if they don't work will only make the arms heavier and more saggy. If you have a ton of time, I MIGHT consider trying it; otherwise I'd just do my best to build the costume without them and maybe use fine thread or something to suspend the arms (or just pump them up enough and keep them light enough to stand on their own).
>>983965
I won't have to put anything directly into the arms, it should be possible to have the costume as a single volume with the pump in the central body.
Or by "external air jets" do you mean simply holes in the arms to provide thrust from escaping air?
Yeah, the air jets might not be necessary except maybe for making the tentacles wiggle, and I don't know how I'd do that.
Getting the arms to behave right by pressure alone though sounds difficult.
>>983966
>Or by "external air jets" do you mean simply holes in the arms to provide thrust from escaping air?
Yeah, that's what I meant. That's not what you were suggesting?
Well it may be an option, but like I said, it's a risky one. But it'd be amusing to have your own wacky waving inflatable arm-flailing Onion-san.
>Yeah, the air jets might not be necessary except maybe for making the tentacles wiggle, and I don't know how I'd do that.
Then don't. Not unless you have lots of time to experiment.
>Getting the arms to behave right by pressure alone though sounds difficult.
I don't think so. Just keep them light - the less weight they have to support, the easier it'll be for them to hold their shape.
Notice how these wings stand up using only air pressure: http://www.yardinflatables.com/Inflatable-Rainbow-Butterfly-Wings-Costume_p_2016.html
>>984353
How easy it would be to experiment depends mainly on what I'm going to make this thing out of, and I have no idea what it will be made of.
Getting the exact properties would be nice, because I think that Blender could do a simulation of it, though I'm not sure how accurately and it would only be for rigidity through air pressure.
Would there be a dramatic decrease in the effectiveness of pressure-based rigidity if I used escape of air to cause wiggling? Because in that case, I might rather try find a way to make the tentacles bend by tugging strings, though that might not work too well either.
>>984371
>How easy it would be to experiment depends mainly on what I'm going to make this thing out of, and I have no idea what it will be made of.
That's a good question. It's really thin fabric that they use for these things, nylon I think but I can't say for sure.
>I think that Blender could do a simulation of it
Really? I thought Blender was purely for 3D modeling, had no idea it could perform simulations of any sort.
>Would there be a dramatic decrease in the effectiveness of pressure-based rigidity if I used escape of air to cause wiggling?
Yeah, I suspect so.
>Would there be a dramatic decrease in the effectiveness of pressure-based rigidity if I used escape of air to cause wiggling?
Well, yes and no. Theoretically, the power required to keep the thing inflated is a product of pressure times leakage rate. With zero leakage (like a vinyl pool toy, for instance) it will remain inflated on its own with no power at all. With a moderate leakage rate through a porous fabric and seams like with the Gemmy Airblown costumes, you need a small blower producing a steady flow rate to maintain pressure. And with a high leakage rate like you would see with having a large Onion-san costume with many oversized ports on the tentacles, you would need a greater amount of flow and power in order to maintain pressure. If your blower is greatly oversized for the size of the costume, you may not notice any pressure drop at all from your jets, but such a large blower will also draw more power and demand bigger, heavier batteries in order to last. If your pump is undersized, the ports may let air out faster than the blower can pump it in, causing the costume to soften and deflate. It's really hard to gauge how much power, blower-size and battery you might need without knowing how much thrust you need to get the arms to act the way you want. The blower I posted above draws a measly 18 watts, but those outdoor airdancers draw HUNDREDS of watts to flail like they do.
>>984371
>Because in that case, I might rather try find a way to make the tentacles bend by tugging strings
Well, tugging aside, I may have thought of a way to hold the tentacles off the ground while keeping them fairly flexible in the lateral direction. Say you have a section of the tentacle which you want to curve upwards, but also be flexible so that it can sway lazily side-to-side. If you lay out the patterns and stitch it up so that that section is straight, but then loosely stitch a single thread along the top of it and pull it somewhat tight to introduce the upwards curvature, the thread would take up the tension instead of the fabric itself along that edge, and so a large degree of flexing/sway can take place with minimal volume change (and thus the pressure will have minimal tendency to stiffen it and straighten it out as it sways). Sorry if my explanation is poor...
>>984409
Here's an illustration of the approximate concept: see how the elbows of this space suit have rippled segments which are under minimal axial tension, and there are two straps taking up the axial tension instead, allowing the elbow to bend effortlessly in that direction despite internal pressure? Think of the straps like the thread, and the ripples like loose wrinkles in the fabric of the tentacle. In the case of the tentacle, since you want it to be rigid in the vertical direction (to hold it up off the ground) but to sway freely in the lateral direction, you'd want the thread on top and (optionally) bottom and the sides of the tentacle to be loose and somewhat wrinkled.
>>984409
>>984420
Not exactly sure what you're saying, but are you saying that:
A) The string which is pulled tight should be on the inside of the curve it is intended to create
B) There should be loose material to make a curve possible
I'm not sure of your explanation, but what I think you're saying is that those blue things on the spacesuit make it impossible for pressure to fully tighten the fabric, and so a change in suit pressure from bending doesn't matter as much.
If that's what you meant, then wouldn't putting in a small hole for air to escape be just as good?
>>983942
Not my specialty per se, but I have made a few costumes before.
Before you get crazy in to mechanics or air pumps, have you considered making the tentacles sealed off from the rest of the costume, then filling them with helium? You can get a small tank of helium at party city, and you may be able to make the tentacles with sheets of mylar cut to the right shape then heat sealed together. Shoot, you may be able to find a mylar baloon that already has some tentacles on it, then just carefully cut them off and fix them on to the rest of the costume.
>>984435
>A) The string which is pulled tight should be on the inside of the curve it is intended to create
Sort of. Mostly, it should be along the axis which you want to be rigid. In other words, if you have thread pulled tight on top and bottom (creating wrinkes around the sides of the fabric), the tentacle will be stiff in the vertical direction but can flex freely in the lateral direction (the wrinkles effectively giving it the freedom of motion, without the internal pressure rigidly holding it straight).
>B) There should be loose material to make a curve possible
Yes. The loose material is the source of flexibility, so that it can flex.
>I'm not sure of your explanation, but what I think you're saying is that those blue things on the spacesuit make it impossible for pressure to fully tighten the fabric, and so a change in suit pressure from bending doesn't matter as much.
Exactly. So if the tentacle is bending to the left, the "right" side with wrinkles can expand freely to counteract the "left" side compressing, and thus the internal pressure has no real tendency to hold it straight and rigid like it normally would.
>If that's what you meant, then wouldn't putting in a small hole for air to escape be just as good?
I guess that depends on how stiff they are, how much thrust you have and how it's oriented, and what kind of behavior you're looking for. The way I see it, the option I suggested would be a fairly easy and "safe" way to just get the tentacles to sway loosely and freely as you move. The jets would be a clever way to get them to move on their own, but it's risky, may fail or may just not behave like you're hoping.
And then there's always the safest option, which is just forgetting about having the tentacles move and just building it rigid while relying on the sheer size and perhaps detail for wow-factor.
>>984441
There's a thought. And if you don't like the mylar finish, you can always have a lightweight fabric exterior with several cells of mylar or latex helium balloons tucked inside, too.
>>984445
That's a good point too. You could just use regular latex baloons, or even the long latex baloons that people make baloon animals out of, then cover them in women's panty hose for that texture.
The reason I mentioned mylar is that you can buy sheets of it, put two sheets together, cut out a custom shape, then use a regular old iron to seal the edges of the two sheets together. Latex baloons, especially covered in another material, would probably look more organic though.
>>984444
So you're saying that if I use bands to create wrinkles to allow it to bend, it will just flop over rather than hold rigid when I'm not tugging the strings?
I guess I'll have to go with allowing air to escape when I pull the strings, though I'd imagine that if the tentacles were large enough they wouldn't even need that since large objects seem to have a tendency to behave in a more plastic manner.
Also, the neat thing about strings is that I could have two main arms controlled like puppets, using four strings spaced around the tentacle to cause bending. I'm still not entirely convinced though that the curve will be significant.
>>984450
>So you're saying that if I use bands to create wrinkles to allow it to bend, it will just flop over rather than hold rigid
Yeah, that's it. Just a way to loosen the sideways motion of the tentacles up so they sway easily when you move instead of just being long, rigid protrusions of the main body. And in my mind at least, it's a fairly simple measure to achieve some basic level of motion.
>I guess I'll have to go with allowing air to escape when I pull the strings
Well that sounds even MORE complicated and tricky, but if you think you're up to it...
>>984407
>>Really? I thought Blender was purely for 3D modeling, had no idea it could perform simulations of any sort.
yeah Blender actually has quite a lot of stuff built in. It has a physics engine and you can even make very simple games in it
>>984464
Now I'm a tad confused.
Wouldn't it be easiest just to make + shaped handles at the base of the tentacles, attached to strings going to the end of the tentacles?
>>984466
As long as you're fine with only being able to move two at a time (and having to deliberately do so) while the rest remain still/rigid, sure. Again, the best approach really depends on what your desired behavior is.
>>984472
The character is usually expressed as having two main tentacles, so that's fine.
I'm just worried about whether even that will work as intended.
So what I'm still wondering is that if I have an inflatable tube with four strings spaced along the sides, and the strings are attached to the ends of the tube, will I be able to flop the tube about by pulling on the strings? Or will it just make the tube want to shrink along one end?
>>986223
I mean step one to flopping about is shrinking on one end and stretching on the other.
>>986264
All I can do is shrink on one end though.
>>983942
Inb4 underage ban
>>986527
Use elastics like bunjie cords or large rubber bands tied together and braided.
>>986527
That will still cause it to bend, though.
I suppose I'll just have to try this out and see what I can do.
What material should I use?
Also, how do I calculate how large a cylinder I can make that will stay stiff with a given pump pressure?
>>988332
If the amount of motion is significant in comparison to the diameter of the tentacle, then yes, significantly.
>>990276
>Also, how do I calculate how large a cylinder I can make that will stay stiff with a given pump pressure?
"Stiff" isn't a very quantitative term. Do you just mean in order to stand up under its own weight? Or to withstand substantial external loads as well?
Also there's a good chance the limiting factor won't be pressure, but flow rate. The lighter materials generally used for inflatable costumes tend to bleed air, and the larger the costume, the more air bleeds through it and the more air must be pumped to maintain pressure.
>>990304
>If the amount of motion is significant in comparison to the diameter of the tentacle, then yes, significantly.
Not exactly clear what this means.
And it just needs to stand up under its own weight.
I suppose that if I know the bleed rate in relation to pressure and area, I can factor that into calculations, unfortunately I don't know how to do any of the calculations nor do I have some sort of table of properties of inflatable-suited materials.
