Best device(s) for this cosplay

I'm going to read this as I respond, because it's easier for me to sort that way than try to remember. ^_^;
That said, sorry if I ask or answer something you elaborate later. Also, I'm bad at the quote thing.

"...then alter a 'fan curve' for how fast the fans rotate depending on temperature and humidity, with a manual override for "just whack it up to full speed please"." 
Is there honestly a reason a complicate it using this? Just to save battery? So far, I'm planning to just connect the helmet to the main battery on my back.

"With the use of MOSFETs you can control fans that are 12v ... would allow you to use fans that were either larger, or more powerful to move the air as needed, while being controlled by a lower voltage microcontroller, say from an Arduino or similar.

I've never got to make anything with MOSFETS, AFAIK. With a fan blowing directly on me, I'm concerned too strong may be too much sensory. I'm also considering to run a hydration line from one of the shoulder pieces, like a hydration backpack. This would likely go down the tube from the right side of my mask, while air come in my left side, eg through the left hose. 

"You may also find that you only need an intake , or that you need two exhaust, with no intake, or only one intake, depending on how you want to setup the air pressure.'
Would you like to expand upon this? I'm still considering how I'll want the exhaust to work, though I'm looking at intake being through the right "ear" bubble.

"A small OLED or LCD screen can possibly do this for you"

My question here is how would I make it work in this confined space? Ideas? It's one of the two things that's been holding up my project. Specific models in mind? I have been wondering if there's a small LED projector that works by reflection, but that may be worth it's own post if not answered here.

"or if you find a small epaper/eink display then it only has to update and refresh the screen every few seconds or minutes rather than using power for the whole screen constantly"
Same as above, but this simplicity seems closer to what I wanted , except quick alerts if I included a form of sensor to detect behind me. Can this be updated more quickly with more power? Eg I trigger it to redraw the screen if something is 5ft behind me? That sounds AMAZING!

"this could be a microcontroller or something 'beefier' with an operating system like a Raspberry Pi (such as a Zero or Zero W) but then that introduces battery drain and failure points and waiting for it to boot."

I'm perfectly fine with a "Boot Sequence". Hell, I can make that work amazingly!
Imagine it's booting up, and plays the NES "Secret Area" music? Then when completed, it plays the "Same Start" music?! It making that music could also tell me my battery is dying, others here it as I seem to rush off (not knowing to change my battery).

"you're wanting more than a dummy 'push button, activate motor' or 'I'm reusing a nerf gun' then you're probably looking at using steppers and a microcontroller, because wouldn't it be cool to have it synchronised with sound and light actions too?"
I've planned it to be a mix of parts in there, but I NEVER considered having it change the lights! Even if I do repurpose a nerf gun or something, I can have a button to push with it to do so! Thanks!


"It's probably easier to look at this from a 'what would it take to do each type of thing, does something already exist?" 
That's why I'm asking. I know other ways to do most of this, but did not keep up with tech over 5 years.

"Compressed air is going to have a limit"
There's a trick you can do with compressed air that it shoots ice crystals. I just try to leave it vague because it can be dangerous if not handled correctly.

"Ping pong balls are relatively cheap, light. An alternative would be the nerf balls that blasters use, or a nerf blaster itself. Maybe the dog toy version."
Thanks! Will look into. Like I said, can still connect a trigger to a light button... but I may want to use it manually anyhow, eg on stage.

"I'd avoid fire. If only because of health and safety paperwork at cosplay conventions."
I hear you. I've been friends with some convention owners, and their rules for attractions are different usually than guests. They also make exceptions for some cosplay props. I remember one year I cosplayed Raiden while wearing a gadget that covered my body in thousands of volts of static electricity. Sparks came from my fingertips near metal. For some reason, people didn't want to give me a high five. 

Point is, I'd probably work whatever out with the head of a convention in advance, because nobody else would even know I have certain things until I'm up on stage. 

...Now I'm wondering if I may want redo how the costume attaches in the future. My current way is a black catsuit, with velcro and a couple straps. Now I'm imagining keeping guests completely in the dark that I have the full costume UNTIL the competition or showcase starts. To do so, I'd be connecting CERTAIN points to the Zero Suit Samus (her blue outfit), so I can wear it UNDER the costume... but I'd def need one that's breathable unless I add fans through my body. 

There is a head up display project on Hackaday that may be worth a look

https://hackaday.io/project/12211-arduino-glasses-a-hmd-for-multimeter

Alternatively there are some off-the-shelf HUD systems for motorcycle helmets these days which might work.

Thanks for the feedback! I'll definitely look into the LEDs! For the interconnections, I actually have multiple reasons for this method that you may find clever!

First, I'm AuDHD, and will not constantly be looking to see if certain lights or on (that's just a mental drain). I don't want to risk a photo with someone that one leg died without us noticing, or them being nice. I also don't want to have to access these compartments to change them, or carry multiple batteries in case. 

In fact, I plan to run all of these from a single battery in my back: I'm undecided if one of my large 5V packs I used for robotics, or a higher voltage battery. I grew up in karate exercising with a medicine ball, and used to section hike the Appalachian Trail with 60lbs in my pack. I def appreciate the alternative, but my bigger concern is how I would want to safely attach one to my back. That's leaning me towards my huge 5V USB battery, but I've not calculated if I'm going over 2.1A yet.

The helmet power, I agree with just keeping it on: The Kiss Method. I plan to have it connect to the battery as well, so it's only on while connected.

Thanks! I didn't see an option to add a photo until you said something. It was late, and I was looking for an "attach image" button, not it to be in the interface on my phone like in MS Word lol! Thanks for posting yours, I edited my post to include the lose schematic!

I'd consider making things modular to keep the battery size down and interconnections minimal. Button batteries can be used where power consumption isnt high. 

I'd leave the fans on continuously to simplify things, maybe have a OFF switch when its not being worn. Get some slow itty bitty ones unless you are planning to have fight scenes with John Wick. 

The trim could use WS2812 LED strings. They do hog power, but have the best flexibility, you can do rainbow effects or have the colors change, or variable flashing and dimming. 

These look cool 

Some images of the character might help people here visualise the costume.

There appear to be several variations as the character has evolved.

Looks like their might be plenty of room in the shoulders for stuff.

Amethyst said:

-An intake and exhaust fan in the helmet, like RasPi mini fans (5v), for temperature and breathing. I plan to fit these in the "ears" of the helmet that the hoses attach to.

Depending on budget and space available, I would have a dedicated microcontroller for fan control and combine that with at least a temperature sensor, could be combined with a humidity sensor and then alter a 'fan curve' for how fast the fans rotate depending on temperature and humidity, with a manual override for "just whack it up to full speed please".

With the use of MOSFETs you can control fans that are 12v, though it then depends on your power supply, but that would allow you to use fans that were either larger, or more powerful to move the air as needed, while being controlled by a lower voltage microcontroller, say from an Arduino or similar.

You may also find that you only need an intake , or that you need two exhaust, with no intake, or only one intake, depending on how you want to setup the air pressure.

Amethyst said:

-Some kind of screen in the helmet that can tell me information from the board. Looking at battery level, temperature, and possibly proximity sensor information.

A small OLED or LCD screen can possibly do this for you, or if you find a small epaper/eink display then it only has to update and refresh the screen every few seconds or minutes rather than using power for the whole screen constantly. Again this could be a microcontroller or something 'beefier' with an operating system like a Raspberry Pi (such as a Zero or Zero W) but then that introduces battery drain and failure points and waiting for it to boot.

Amethyst said:

Arm Blaster:

-Ice Beam using compressed air, unless there's a good electronic alternative? 

-Ping pong or Airsoft pellets. Which would be cheaper to build? Doesn't need to be high pressure, of course. 

-Fireballs by flash paper and cotton with a glow plug. Suggestions on safest way to control it? Not sure I want a 12v stepper in my arm cannon, not sure if a lower voltage would do the job?

Hm, well if you're wanting more than a dummy 'push button, activate motor' or 'I'm reusing a nerf gun' then you're probably looking at using steppers and a microcontroller, because wouldn't it be cool to have it synchronised with sound and light actions too? It's probably easier to look at this from a 'what would it take to do each type of thing, does something already exist? does it need to be more complicated?' than trying to build it from the ground up off the bat.

Compressed air is going to have a limit, but perhaps there's something like the airzooka that would work in a smaller confinement?

Ping pong balls are relatively cheap, light. An alternative would be the nerf balls that blasters use, or a nerf blaster itself. Maybe the dog toy version.

I'd avoid fire. If only because of health and safety paperwork at cosplay conventions. 

You have a very good point about the fans! Thankfully, I was using it for reference, since there's those circle bulgest at the side. I'm still not 100% on how I'm making the helmet, but I'm looking at using hose for the front part. If I keep the circle parts on the side open, I can push air through the hose, and keep the fan blocked by that layer in the helmet!

So, thanks again for pointing that out, before I start! For voice changer, I got one for batteries (AAAs) years ago for this. I def could put it in and connect the 3v line to power it no prob. Then I also realized by maybe needing that area open for air as just mentioned: Nobody may know who I am anyhow if I mirror it: I used to practice voice acting and have a voice range that goes from Sailor Moon to Sir Integra Hellsing.

Very cool suit idea.

The fans are a great idea - need to get that CO2 out of the helmet, although putting fans at the ears may make it hard to hear anything else.

If you can find a cheap voice changer module, or rig a voice changer phone app to play from a speaker in the suit, nobody will know who you are.