The Winter Soldier: a few thoughts on the arm
(I have a new icon! *puffs up* ^^)
This turned out more popular than I had expected, so I decided to elaborate on it a little.
I've edited the CW post, which now in place of that fragment has a link leading here.
I'm a somewhat unusual animal in this fandom, since most of this comic book esthetic (or rather: superhero esthetic) is what puts me off rather than attracts, and I like MCU in spite of that, instead for that. At the same time, I regard it on two levels:
1. personal taste, which finds all those capes, gaudy colors and sculpted costumes mostly ridiculous instead cool;
2. objective, intellectual interest, which finds it fascinating and not-to-be-dismissed in cultural terms.
So, the latter part of me realizes just fine that the design of the Winter Soldier's arm is all about the look that doesn't really need to be sensible, as long as it is impressive. Certainly at this side of the fourth wall and at least partially inside of it too (if you have any doubt, look at the red star; it's been put there for a reason, not just by MCU design team, but also by Hydra's smoke & mirrors department). However, the former part is directly connected to my fannish hindbrain, so as soon as it takes a break in laughing, it starts coming up with explanations, reasonings and desperate attempts to convince itself that this comic book science is not as comic as it looks. So, make no mistake, all the content of this entry is still more comic than science, but this way it's more fun for me, and as I know, at least for some of you. :)
Still, disclaimer first: I'm not coming from any professional stance; it's all just a little of common sense and more or less common, easily available knowledge. If you happen to be able to offer a professional view, you're most welcome to jump in and tell me I'm babbling bullshit here, because X, Y and Z. And if you don't, you're still welcome to offer alternative ideas, because I'm offering nothing else anyway - just hypotheses, theories and wild headcanons. Oh, and to be clear: all the time I'm taking into consideration only the MCU canon.
~*~
#tell me how the arm works captain america 3
give me bad pseudo science talk dirty to me
ilvalentinos/Tumblr
I. The general shape
It's artificial. It's metal. Presumably all the way down inside, not a single piece of the original limb remaining. Why in hell is it an exact copy of a human arm, down to the hints of 'bones' under the 'skin'? And why is it so inconsistent in it, imitating the form, but not the covering?
It's for aiding the neural connection. The keyword here is proprioception. Bucky clearly is able to manipulate things without looking, which means he has to not only get some sensory feedback, but also be aware of the relative position of the arm's all parts very precisely, the same way one is aware of real limbs. It could have been achieved easiest by sort of inserting the prosthesis into the phantom of the original arm, so the brain would have just accepted the replaced hardware and applied the old software, the device driver, so to speak. That's why the shape needed to be as exact as possible. This applies also to the range of motion: notice it does everything a real arm can do, but also nothing that a real arm cannot do - no bending backward or 360° rotation, or whatever, even though it could and should be achievable from the engineering point of view; in many cases easier than imitating the pull of tendons and all. At the same time, that's also why the texture and coloring did not matter, because it was all about cheating the feeling 'from inside', not the other senses. We can assume he might prefer catching things with the hand gloved not only for better grip and to avoid attracting attention, but also because it feels more tool-like when on sight.
II. Why is it kept bare, then?
All his fighting outfits (except one) keep it on oh-so-shining display, even though the whole rest of the look suggests the intention of concealment.
Well, in camouflage terms the silvery shine is stupid (if admittedly pretty) no matter how you twist the logic (*squints heavily* maaayybe blackening the metal itself would weaken it, whatever metal it's supposed to be... and simple putting a dark matte paint on was inconvenient, because it kept rubbing off and particles kept falling inside and blew out circuits or clogged bearings, or whatever), but the lack of cover is about cooling. Divided plates certainly help, but in bursts of activity it must be heating like an overworked laptop or hard-pushed drill. If covered, this could jam the mechanism (thermal expansion of the metal, melting of cable insulation and tiny processors; you name it) and/or ignite the sleeve's fabric. Also...
...shifting plates could pinch the fabric's folds, hindering moves. A side note: have you noticed that this is actually the only thing that makes the arm look inhuman? Everything else either deepens the human illusion (shape) or can be taken for armor or costume (the metal, the star). Accordingly, he probably has not much of conscious control over it. A mechanical equivalent of gooseflesh? :) Or raising hackles, which is technically the same thing anyway.
Okay, then what about that one exception - the two-sleeved jacket in the blowing-up-Fury's-car scene? My exquisitely sophisticated answer: no freaking idea. :P
III. How does it even hold on, for sanity's sake?
Comic books science treats characters like collectible figures - take off a piece, screw on a new one, voilà! Live bodies, though, aren't marshmallows or clay golems. They are complicated inside.
It's heavy. The whole “blah blah heightened healing factor” can only take things so far - there's no way in hell it hangs just by the skin and some miserable remains of the shoulder joint. It still needs an extended frame for distributing the weight and pull. Since there's apparently no original bones inside the arm itself, the frame needs to go the other way: inside the shoulder and chest, though not as solid blocks, because the point is in gradual, intertwining passing from the artificial to the natural. So, I'd say the seam is not a simple border, but a layer of skin on the metal (possibly perforated, to lessen the risk of necrosis and make the plate more ingrown) that continues underneath for an inch or three. More important are bones, though. I'd say the minimum is a metal left clavicle and scapula; possibly also a few top ribs. (Which by the way makes another reason for the necessity of efficient cooling, if we take under consideration the thermal conductivity of metal and the increased amount of its contact area to the flesh.) A popular fanon is combination of a permanent ingrown socket with the disconnectable rest (so, a collectible figure-like, after all), which I think is sensible, but I'd add a restriction that the option must be not often used. You don't want to mess with proprioception more than absolutely necessary - it gets confused easily and no wonder, since it hasn't really evolved for plugging and unplugging body pieces at a whim. Or, y'know, ever. That's why the 'software' can have troubles with rebooting, which in real life happens in some cases even to limbs splinted for a length of time. And even in the arm itself, the most vulnerable is certainly not any mechanic part, but the whole neural wiring. We can assume it's as deep under the casing's surface as possible, everywhere. If so, this means in emergency he can lose quite a portion of the casing and still have the motion control, because that would be the last thing to go, with the detection of pressure being the first (because the plates must be what passes the signal to the receptors). Not quite unlike in living flesh. The whole disconnection problem by the way explains why simple repairs involve a trembling technician with a bunch of trigger-happy guards, instead of the safer option of taking the thing off to some remote lab, fixing it on a table and bringing it back to plug in.
Still, Houston Hydra, we have another problem here. It doesn't just need to not fall off; it also needs to move.
...And the cut goes straight through the pectoralis. Across the fibers' direction, all of them. Not to mention other minor muscles. Yikes... Now, that's supposed to be brushed aside with “something something super strength”, but it won't do. Come on, even in the comic book physics it doesn't matter how hard you pull at a rope, if the rope has been severed! So we need to go around it by “it only looks like severed”. Synthetic muscles maybe? Either whole ones replaced, or single fibers ingrown in the natural ones. And that's another reason for the seam to be multilayered, not just welded-zipped edge to edge.
IV. Okay, but how much heavy?
The arm itself plus the leftside metal frame sends the balance to hell, which besides in long term does ugly things to the spine. Inconvenient for a fighting machine. So, counterweights needed? Following this logic we'll end with the whole metal skeleton, which would be not only comic book science, but also comic book economy and comic book tactic, because:
1. at this point you can as well pick out the brain and put it in a jar at the top of an android body, or use AI, or just have someone remote-operating it;
2. you get a sniper for whom you need to dig through the building's papers and check the structural load limit of the roof every time before putting him on a vantage point; also, he can't use motorcycles, small cars or boats, light aircraft and basically any vehicle where center of balance matters.
So we need again to use the “it only looks so” solution. Or, this time rather “it's heavy indeed, but not as heavy as it could be”. We can assume that a lot of creative effort has been put into reducing the general sum of mass, but also - again - distributing it. Most obvious way is using as much hollow spaces as possible, in place of solid blocks (even though the arm itself still must be a very compact construction, because it's a lot of functions to fit into so little room; all hail the miniaturization of the data transmission & computing stuff). Tube is actually more durable and stress-resilient shape than solid rod, which means the bones don’t need to be that much massive. Vibranium begs for attention at this point, but MCU Civil War seems to indicate it's not really in play here... (yet?). This solution trumps #2 to some degree, of course, but #1 remains. Anyway, the only part that must be really as tough as it looks, is the casing, while the core can use lighter materials. A convenient side-effect would be small parts with low inertia, which means less g-force impact with sudden changes of acceleration, and therefore lesser risk of messing everything inside with every punch. Not to mention less cumulated weight on joints every time he holds the arm straight down by side. Also, the human-like form, with the upper arm broader than the lower arm, is actually helpful in keeping the center of balance close to the main body mass (which is why it has evolved this way in the first place, duh). And within the chest, bones aside, the synthetic muscles are another opportunity to save mass. Think in direction of the “high durability + small weight” sort of fibers, like spider web proteins or fullerenes (not necessarily these exact ones, because I'm not sure anyway how the latter work with stretching, especially repetitive). Their relatively low toxicity is a nice bonus. The ideal goal would be lowering the mass of the chest's left side more than the right side's, which would make it up for the arm's mass. The result would be admittedly still awkward, compared to the regular body, but here's where this “blah blah super strength” comes in handy and finally makes some actual difference. Also, we can bet he has learned to be hyperaware of his balance and constantly compensate for it without even consciously thinking anymore. Not very unlike any person with any sort of prosthesis. Anyway, the brain doesn't need to develop anything new here, just recalibrate the old. Downside is that with the arm unplugged his balance temporarily gets really thrown off, even more than immediately after when he lost the original one.
V. Fingertips
It's actually hard to tell what exactly are they like...
(Besides that they look like they belong in movie mistakes, the 'design continuity' sort. Then again, all footage that’s actually in the movie itself is consistent, and everything else - two last pics - comes from promo stills and one deleted scene, so we can assume the changes are the result of digital post-production. Which I think means only the first two pics should be considered canon actual.)
...but it seems they're roughly human-shaped. Which is the one place where the shape imitation is counterproductive instead helpful, because the whole point of having rounded pads is that they are also soft and yielding. If you wonder why does it matter and your imagination isn't helpful, test picking up small items from flat unyielding surfaces with at least two thimbles. You may also notice that it works marginally better with flat-topped ones. In general, the more perfect curve, the less efficient it is, which means that at worst he can't pick up anything more narrow than half a fingertip - pencil, coin, hair tie... He'd have it actually much better not with the normal human shape, but the reverse of it: flat inside and convex outside, narrowing downward. So, basically sort of broad and non-cutting pincers. As a bonus, it would made quite efficient claws, though more useful for digging in (say, concrete surface or small crevices in whatever) than taking a talons-like hold (because of the round edge and flat inward side).
(You better appreciate this crappy scheme. I hate working with Corel...)
However, we can interpret the clumsy design as in-universe deliberate, since as far as Hydra is concerned, the only he needs to handle is weapon, which is big enough, and for rare exceptions he still has the other hand.
VI. Why the glove, why fingerless, and why only one?
For a good grip, one needs good friction. Which means at least one of the two - either the manipulator or the object - can't be smooth and hard. Which in this case poses a problem, when the most often handled object is a gun... A solid, vice-like squeeze can make up for lack of friction, but sniper rifles are freakingly precise instruments and I doubt they take such treatment well.
Leather can give even better grip than live skin, because it doesn't feel when it gets chafed and pulled. (Even if you're an epitome of a fragile lady, you don't really need a strong friend for opening stubborn bottles and jars, if you happen to be in possession of well fitting leather gloves; you're welcome.) However, it works best in the center of the palm, while covering the fingertips gives only protection paid with lose of precision, which in case of metal fingers would be gaining nothing with losing what little was there to start with. Granted, leather could work as pads, but it would need to keep adhered to the metal, not sliding against it. A drop of glue into each of the glove's fingers before pulling it on? Hard to apply in the correct spot, risky for the plates joints and still easy to tear off. Better solution is just combining a fingerless glove and glued on pads (doesn't have to be leather; fast setting, rubbery paint would be even better). And besides, cooling is a factor again.
(At least one fan has offered a theory of the glove aiding the sensory feedback, but I'm not really convinced. If anything, this could rather confuse the receptors, because the taut leather would spread any focused pressure onto nearby plates. Let's not forget that, unlike the elastic live skin, they are stiff.)
The other hand is the only that could really use the protection, yet it remains bare, because it's the one used for more delicate tasks and the certainty of losing precision doesn't calculate against only a possibility of injury. Besides, healing factor.
VII. Powering
Rarely getting any attention in fics and all, but actually presenting the most troublesome part of the matter, I'd say...
Perhaps most of fic writers just assumes it sort of obvious by default that the arm is powered the same way as the remaining limbs? Well, it can't be. Live muscles aren't powered from outside; they get only a constant supply of fuel of which they generate the energy they need to contract. And the arm has the full range of motion in all parts, shoulder to fingertips, so there must be something providing the pull, repeated after every joint all the way down to the knuckles. Should we assume that there are also synthetic muscles along the arm's length, and that they copy even the chemical processes of the real ones? If so, they’d need a copy of the circulatory system, too, because in spite what one could think, blood’s primary function isn’t rising movie ratings. But anyway, canon clearly indicates there's electricity at work (the arm can get short-circuited and there are wires visible in damaged parts). Granted, this could be just for the neural wiring, but even this must take this electricity from somewhere. (I wonder also about how much does the loss of energy in the transmission matter in this case, but metals have lower resistivity than live tissue anyway, if I'm not mistaken, so maybe that's not really a factor here.)
Technically, live cells already use electricity all the time, so why not just increase the output along the seam, right? Not really, no. Humans aren't electric eels, and anyway we aren't talking here just more, but orders of magnitude more, if we assume the synthetic muscles aren't self-powered, and even if they are, they still can't be self-fueled, unless the comic book science has happily invented a perpetual chemistry. So, at the end of the day it all boils down to the source of fuel even more than to the form of power. I've been seeing around theories about hooking it up to the body's metabolism, but I don't find it really plausible. First, humans aren't hummingbirds either, and second, okay, so let's apply the comic book science and tweak the metabolic engine, yadda yadda super serums, blue glow and all. (Now I can't help a very insistent vision of the mitochondrion in every and each cell popping out a twin.) The result? A fighting machine that needs a refuel break every few minutes... There's a reason hummingbirds are so tiny AND still spend most of time on feeding. And this not even taking into account that besides the arm, the serum-tweaked, fleshy rest of him already burns food like a combustion furnace. Rather sooner than later we’ll run into the limit beyond which he burns faster than he’s able to eat. The only way around it would be applying the comic book science also to the food, yadda yadda super powerade thousand times as energetic as pure sugar and 100% energy convertible.
The alternative approach is stop trying to be fancy about it, and just use a damn battery... Which by the way would solve the electric eel problem, because hey, you do realize that upping the natural voltage of the live cells would fry them, right? (And nope, we're totally not even thinking about replacing the fragile wet human stuff with anything fancier on the cellular level, because we have already talked about it. Brain, jar, android.)
We have two design options here:
A. replaceable, disposable whatsit;
- must be accessible without unplugging the unpluggable part, therefore through the casing;
- must have a high output without being too large; isotope generator? another reason for the efficient cooling... arc reactor? in such case don't tell Tony that Hydra had it first... (Howard, I'm suspiciously squinting at you); then again, the arm hardly needs even as much as tenth part of the Stark suit's power demand;
B. rechargeable accumulator cell;
- can be inaccessible without taking apart the arm (or even the socket), but instead must have a charging outlet;
- still must have a high storage capacity without being too large; some lithium-like [insert another handy whatsit from the Marvel Periodic Table Mendeleev Haven't Heard OfTM] battery.
Still, each option means a huge (maybe the biggest) part of that mass amount we have talked about in #IV must be the power source. So, whatever it is, must be placed in the higher part of the arm or within the socket.
Also, the all three options - tweaking the metabolic engine, replaceable battery, rechargeable battery - mean that everything works fine as long as there's Hydra to provide (if you think the third option doesn't, think about dedicated plugs). Great news for Hydra. Bad news for Bucky and fic writers. Then again, limits are possibilities. :)
Personally I think the first option sucks the most, because it could not just render the arm useless, but also make him drop dead even when rolling in food. Actually I'm pretty sure Hydra wouldn't like to risk it, so there'd have to be some automatic safety switch, “low power level = stop powering the arm”. That's actually what live bodies do in extreme circumstances, cutting off the energy for the outer parts to save the vitals until there's a chance to refuel again.
Third option seems most convenient for Bucky-in-the-wind, as long as the recharging port isn't unique in shape, voltage and all, or at least can be replaced (Tony?). Upsides: he lives even when the arm is a dead weight; also, the power source is relatively easy to get. Downsides: once in a while he needs to spend some time (an hour daily? weekly?) plugged in; also, the arm won't survive for long out of civilization, because forests and mountains sadly lack trees with power sockets. Then again, 'long' is a negotiable term here (in all three options, to some extent), and this is where the comic book science can come in handy, because one needs to barely stretch the logic, instead of blatant dismissing it.
~*~
Used images:
Gif by buckes, with the author's permission.
Photos courtesy of Screencapped.org, Superheroscreencaps.com and SebastianStanFrance.com.
Modified illustration from OpenStax, Anatomy & Physiology. OpenStax CNX.
Other graphics are mine.
Meta on the subject by others, some 40% of which I found only after writing my own, and of course thought “Why have I even bothered”. You can play guessing which ones make the remaining 60%. You may also notice I agree with some parts, and disagree with others:
[post] by therealdeepsix
[posts] by cptsassrogers
[post] by phoenixgryphon
MCU Winter Soldier's Arm by shakespearesconesandstars
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This turned out more popular than I had expected, so I decided to elaborate on it a little.
I've edited the CW post, which now in place of that fragment has a link leading here.
I'm a somewhat unusual animal in this fandom, since most of this comic book esthetic (or rather: superhero esthetic) is what puts me off rather than attracts, and I like MCU in spite of that, instead for that. At the same time, I regard it on two levels:
1. personal taste, which finds all those capes, gaudy colors and sculpted costumes mostly ridiculous instead cool;
2. objective, intellectual interest, which finds it fascinating and not-to-be-dismissed in cultural terms.
So, the latter part of me realizes just fine that the design of the Winter Soldier's arm is all about the look that doesn't really need to be sensible, as long as it is impressive. Certainly at this side of the fourth wall and at least partially inside of it too (if you have any doubt, look at the red star; it's been put there for a reason, not just by MCU design team, but also by Hydra's smoke & mirrors department). However, the former part is directly connected to my fannish hindbrain, so as soon as it takes a break in laughing, it starts coming up with explanations, reasonings and desperate attempts to convince itself that this comic book science is not as comic as it looks. So, make no mistake, all the content of this entry is still more comic than science, but this way it's more fun for me, and as I know, at least for some of you. :)
Still, disclaimer first: I'm not coming from any professional stance; it's all just a little of common sense and more or less common, easily available knowledge. If you happen to be able to offer a professional view, you're most welcome to jump in and tell me I'm babbling bullshit here, because X, Y and Z. And if you don't, you're still welcome to offer alternative ideas, because I'm offering nothing else anyway - just hypotheses, theories and wild headcanons. Oh, and to be clear: all the time I'm taking into consideration only the MCU canon.
~*~
#tell me how the arm works captain america 3
give me bad pseudo science talk dirty to me
ilvalentinos/Tumblr
I. The general shape
It's artificial. It's metal. Presumably all the way down inside, not a single piece of the original limb remaining. Why in hell is it an exact copy of a human arm, down to the hints of 'bones' under the 'skin'? And why is it so inconsistent in it, imitating the form, but not the covering?
It's for aiding the neural connection. The keyword here is proprioception. Bucky clearly is able to manipulate things without looking, which means he has to not only get some sensory feedback, but also be aware of the relative position of the arm's all parts very precisely, the same way one is aware of real limbs. It could have been achieved easiest by sort of inserting the prosthesis into the phantom of the original arm, so the brain would have just accepted the replaced hardware and applied the old software, the device driver, so to speak. That's why the shape needed to be as exact as possible. This applies also to the range of motion: notice it does everything a real arm can do, but also nothing that a real arm cannot do - no bending backward or 360° rotation, or whatever, even though it could and should be achievable from the engineering point of view; in many cases easier than imitating the pull of tendons and all. At the same time, that's also why the texture and coloring did not matter, because it was all about cheating the feeling 'from inside', not the other senses. We can assume he might prefer catching things with the hand gloved not only for better grip and to avoid attracting attention, but also because it feels more tool-like when on sight.
II. Why is it kept bare, then?
All his fighting outfits (except one) keep it on oh-so-shining display, even though the whole rest of the look suggests the intention of concealment.
Well, in camouflage terms the silvery shine is stupid (if admittedly pretty) no matter how you twist the logic (*squints heavily* maaayybe blackening the metal itself would weaken it, whatever metal it's supposed to be... and simple putting a dark matte paint on was inconvenient, because it kept rubbing off and particles kept falling inside and blew out circuits or clogged bearings, or whatever), but the lack of cover is about cooling. Divided plates certainly help, but in bursts of activity it must be heating like an overworked laptop or hard-pushed drill. If covered, this could jam the mechanism (thermal expansion of the metal, melting of cable insulation and tiny processors; you name it) and/or ignite the sleeve's fabric. Also...
...shifting plates could pinch the fabric's folds, hindering moves. A side note: have you noticed that this is actually the only thing that makes the arm look inhuman? Everything else either deepens the human illusion (shape) or can be taken for armor or costume (the metal, the star). Accordingly, he probably has not much of conscious control over it. A mechanical equivalent of gooseflesh? :) Or raising hackles, which is technically the same thing anyway.
Okay, then what about that one exception - the two-sleeved jacket in the blowing-up-Fury's-car scene? My exquisitely sophisticated answer: no freaking idea. :P
III. How does it even hold on, for sanity's sake?
Comic books science treats characters like collectible figures - take off a piece, screw on a new one, voilà! Live bodies, though, aren't marshmallows or clay golems. They are complicated inside.
It's heavy. The whole “blah blah heightened healing factor” can only take things so far - there's no way in hell it hangs just by the skin and some miserable remains of the shoulder joint. It still needs an extended frame for distributing the weight and pull. Since there's apparently no original bones inside the arm itself, the frame needs to go the other way: inside the shoulder and chest, though not as solid blocks, because the point is in gradual, intertwining passing from the artificial to the natural. So, I'd say the seam is not a simple border, but a layer of skin on the metal (possibly perforated, to lessen the risk of necrosis and make the plate more ingrown) that continues underneath for an inch or three. More important are bones, though. I'd say the minimum is a metal left clavicle and scapula; possibly also a few top ribs. (Which by the way makes another reason for the necessity of efficient cooling, if we take under consideration the thermal conductivity of metal and the increased amount of its contact area to the flesh.) A popular fanon is combination of a permanent ingrown socket with the disconnectable rest (so, a collectible figure-like, after all), which I think is sensible, but I'd add a restriction that the option must be not often used. You don't want to mess with proprioception more than absolutely necessary - it gets confused easily and no wonder, since it hasn't really evolved for plugging and unplugging body pieces at a whim. Or, y'know, ever. That's why the 'software' can have troubles with rebooting, which in real life happens in some cases even to limbs splinted for a length of time. And even in the arm itself, the most vulnerable is certainly not any mechanic part, but the whole neural wiring. We can assume it's as deep under the casing's surface as possible, everywhere. If so, this means in emergency he can lose quite a portion of the casing and still have the motion control, because that would be the last thing to go, with the detection of pressure being the first (because the plates must be what passes the signal to the receptors). Not quite unlike in living flesh. The whole disconnection problem by the way explains why simple repairs involve a trembling technician with a bunch of trigger-happy guards, instead of the safer option of taking the thing off to some remote lab, fixing it on a table and bringing it back to plug in.
Still, Houston Hydra, we have another problem here. It doesn't just need to not fall off; it also needs to move.
...And the cut goes straight through the pectoralis. Across the fibers' direction, all of them. Not to mention other minor muscles. Yikes... Now, that's supposed to be brushed aside with “something something super strength”, but it won't do. Come on, even in the comic book physics it doesn't matter how hard you pull at a rope, if the rope has been severed! So we need to go around it by “it only looks like severed”. Synthetic muscles maybe? Either whole ones replaced, or single fibers ingrown in the natural ones. And that's another reason for the seam to be multilayered, not just welded-zipped edge to edge.
IV. Okay, but how much heavy?
The arm itself plus the leftside metal frame sends the balance to hell, which besides in long term does ugly things to the spine. Inconvenient for a fighting machine. So, counterweights needed? Following this logic we'll end with the whole metal skeleton, which would be not only comic book science, but also comic book economy and comic book tactic, because:
1. at this point you can as well pick out the brain and put it in a jar at the top of an android body, or use AI, or just have someone remote-operating it;
2. you get a sniper for whom you need to dig through the building's papers and check the structural load limit of the roof every time before putting him on a vantage point; also, he can't use motorcycles, small cars or boats, light aircraft and basically any vehicle where center of balance matters.
So we need again to use the “it only looks so” solution. Or, this time rather “it's heavy indeed, but not as heavy as it could be”. We can assume that a lot of creative effort has been put into reducing the general sum of mass, but also - again - distributing it. Most obvious way is using as much hollow spaces as possible, in place of solid blocks (even though the arm itself still must be a very compact construction, because it's a lot of functions to fit into so little room; all hail the miniaturization of the data transmission & computing stuff). Tube is actually more durable and stress-resilient shape than solid rod, which means the bones don’t need to be that much massive. Vibranium begs for attention at this point, but MCU Civil War seems to indicate it's not really in play here... (yet?). This solution trumps #2 to some degree, of course, but #1 remains. Anyway, the only part that must be really as tough as it looks, is the casing, while the core can use lighter materials. A convenient side-effect would be small parts with low inertia, which means less g-force impact with sudden changes of acceleration, and therefore lesser risk of messing everything inside with every punch. Not to mention less cumulated weight on joints every time he holds the arm straight down by side. Also, the human-like form, with the upper arm broader than the lower arm, is actually helpful in keeping the center of balance close to the main body mass (which is why it has evolved this way in the first place, duh). And within the chest, bones aside, the synthetic muscles are another opportunity to save mass. Think in direction of the “high durability + small weight” sort of fibers, like spider web proteins or fullerenes (not necessarily these exact ones, because I'm not sure anyway how the latter work with stretching, especially repetitive). Their relatively low toxicity is a nice bonus. The ideal goal would be lowering the mass of the chest's left side more than the right side's, which would make it up for the arm's mass. The result would be admittedly still awkward, compared to the regular body, but here's where this “blah blah super strength” comes in handy and finally makes some actual difference. Also, we can bet he has learned to be hyperaware of his balance and constantly compensate for it without even consciously thinking anymore. Not very unlike any person with any sort of prosthesis. Anyway, the brain doesn't need to develop anything new here, just recalibrate the old. Downside is that with the arm unplugged his balance temporarily gets really thrown off, even more than immediately after when he lost the original one.
V. Fingertips
It's actually hard to tell what exactly are they like...
(Besides that they look like they belong in movie mistakes, the 'design continuity' sort. Then again, all footage that’s actually in the movie itself is consistent, and everything else - two last pics - comes from promo stills and one deleted scene, so we can assume the changes are the result of digital post-production. Which I think means only the first two pics should be considered canon actual.)
...but it seems they're roughly human-shaped. Which is the one place where the shape imitation is counterproductive instead helpful, because the whole point of having rounded pads is that they are also soft and yielding. If you wonder why does it matter and your imagination isn't helpful, test picking up small items from flat unyielding surfaces with at least two thimbles. You may also notice that it works marginally better with flat-topped ones. In general, the more perfect curve, the less efficient it is, which means that at worst he can't pick up anything more narrow than half a fingertip - pencil, coin, hair tie... He'd have it actually much better not with the normal human shape, but the reverse of it: flat inside and convex outside, narrowing downward. So, basically sort of broad and non-cutting pincers. As a bonus, it would made quite efficient claws, though more useful for digging in (say, concrete surface or small crevices in whatever) than taking a talons-like hold (because of the round edge and flat inward side).
(You better appreciate this crappy scheme. I hate working with Corel...)
However, we can interpret the clumsy design as in-universe deliberate, since as far as Hydra is concerned, the only he needs to handle is weapon, which is big enough, and for rare exceptions he still has the other hand.
VI. Why the glove, why fingerless, and why only one?
For a good grip, one needs good friction. Which means at least one of the two - either the manipulator or the object - can't be smooth and hard. Which in this case poses a problem, when the most often handled object is a gun... A solid, vice-like squeeze can make up for lack of friction, but sniper rifles are freakingly precise instruments and I doubt they take such treatment well.
Leather can give even better grip than live skin, because it doesn't feel when it gets chafed and pulled. (Even if you're an epitome of a fragile lady, you don't really need a strong friend for opening stubborn bottles and jars, if you happen to be in possession of well fitting leather gloves; you're welcome.) However, it works best in the center of the palm, while covering the fingertips gives only protection paid with lose of precision, which in case of metal fingers would be gaining nothing with losing what little was there to start with. Granted, leather could work as pads, but it would need to keep adhered to the metal, not sliding against it. A drop of glue into each of the glove's fingers before pulling it on? Hard to apply in the correct spot, risky for the plates joints and still easy to tear off. Better solution is just combining a fingerless glove and glued on pads (doesn't have to be leather; fast setting, rubbery paint would be even better). And besides, cooling is a factor again.
(At least one fan has offered a theory of the glove aiding the sensory feedback, but I'm not really convinced. If anything, this could rather confuse the receptors, because the taut leather would spread any focused pressure onto nearby plates. Let's not forget that, unlike the elastic live skin, they are stiff.)
The other hand is the only that could really use the protection, yet it remains bare, because it's the one used for more delicate tasks and the certainty of losing precision doesn't calculate against only a possibility of injury. Besides, healing factor.
VII. Powering
Rarely getting any attention in fics and all, but actually presenting the most troublesome part of the matter, I'd say...
Perhaps most of fic writers just assumes it sort of obvious by default that the arm is powered the same way as the remaining limbs? Well, it can't be. Live muscles aren't powered from outside; they get only a constant supply of fuel of which they generate the energy they need to contract. And the arm has the full range of motion in all parts, shoulder to fingertips, so there must be something providing the pull, repeated after every joint all the way down to the knuckles. Should we assume that there are also synthetic muscles along the arm's length, and that they copy even the chemical processes of the real ones? If so, they’d need a copy of the circulatory system, too, because in spite what one could think, blood’s primary function isn’t rising movie ratings. But anyway, canon clearly indicates there's electricity at work (the arm can get short-circuited and there are wires visible in damaged parts). Granted, this could be just for the neural wiring, but even this must take this electricity from somewhere. (I wonder also about how much does the loss of energy in the transmission matter in this case, but metals have lower resistivity than live tissue anyway, if I'm not mistaken, so maybe that's not really a factor here.)
Technically, live cells already use electricity all the time, so why not just increase the output along the seam, right? Not really, no. Humans aren't electric eels, and anyway we aren't talking here just more, but orders of magnitude more, if we assume the synthetic muscles aren't self-powered, and even if they are, they still can't be self-fueled, unless the comic book science has happily invented a perpetual chemistry. So, at the end of the day it all boils down to the source of fuel even more than to the form of power. I've been seeing around theories about hooking it up to the body's metabolism, but I don't find it really plausible. First, humans aren't hummingbirds either, and second, okay, so let's apply the comic book science and tweak the metabolic engine, yadda yadda super serums, blue glow and all. (Now I can't help a very insistent vision of the mitochondrion in every and each cell popping out a twin.) The result? A fighting machine that needs a refuel break every few minutes... There's a reason hummingbirds are so tiny AND still spend most of time on feeding. And this not even taking into account that besides the arm, the serum-tweaked, fleshy rest of him already burns food like a combustion furnace. Rather sooner than later we’ll run into the limit beyond which he burns faster than he’s able to eat. The only way around it would be applying the comic book science also to the food, yadda yadda super powerade thousand times as energetic as pure sugar and 100% energy convertible.
The alternative approach is stop trying to be fancy about it, and just use a damn battery... Which by the way would solve the electric eel problem, because hey, you do realize that upping the natural voltage of the live cells would fry them, right? (And nope, we're totally not even thinking about replacing the fragile wet human stuff with anything fancier on the cellular level, because we have already talked about it. Brain, jar, android.)
We have two design options here:
A. replaceable, disposable whatsit;
- must be accessible without unplugging the unpluggable part, therefore through the casing;
- must have a high output without being too large; isotope generator? another reason for the efficient cooling... arc reactor? in such case don't tell Tony that Hydra had it first... (Howard, I'm suspiciously squinting at you); then again, the arm hardly needs even as much as tenth part of the Stark suit's power demand;
B. rechargeable accumulator cell;
- can be inaccessible without taking apart the arm (or even the socket), but instead must have a charging outlet;
- still must have a high storage capacity without being too large; some lithium-like [insert another handy whatsit from the Marvel Periodic Table Mendeleev Haven't Heard OfTM] battery.
Still, each option means a huge (maybe the biggest) part of that mass amount we have talked about in #IV must be the power source. So, whatever it is, must be placed in the higher part of the arm or within the socket.
Also, the all three options - tweaking the metabolic engine, replaceable battery, rechargeable battery - mean that everything works fine as long as there's Hydra to provide (if you think the third option doesn't, think about dedicated plugs). Great news for Hydra. Bad news for Bucky and fic writers. Then again, limits are possibilities. :)
Personally I think the first option sucks the most, because it could not just render the arm useless, but also make him drop dead even when rolling in food. Actually I'm pretty sure Hydra wouldn't like to risk it, so there'd have to be some automatic safety switch, “low power level = stop powering the arm”. That's actually what live bodies do in extreme circumstances, cutting off the energy for the outer parts to save the vitals until there's a chance to refuel again.
Third option seems most convenient for Bucky-in-the-wind, as long as the recharging port isn't unique in shape, voltage and all, or at least can be replaced (Tony?). Upsides: he lives even when the arm is a dead weight; also, the power source is relatively easy to get. Downsides: once in a while he needs to spend some time (an hour daily? weekly?) plugged in; also, the arm won't survive for long out of civilization, because forests and mountains sadly lack trees with power sockets. Then again, 'long' is a negotiable term here (in all three options, to some extent), and this is where the comic book science can come in handy, because one needs to barely stretch the logic, instead of blatant dismissing it.
~*~
Used images:
Gif by buckes, with the author's permission.
Photos courtesy of Screencapped.org, Superheroscreencaps.com and SebastianStanFrance.com.
Modified illustration from OpenStax, Anatomy & Physiology. OpenStax CNX.
Other graphics are mine.
Meta on the subject by others, some 40% of which I found only after writing my own, and of course thought “Why have I even bothered”. You can play guessing which ones make the remaining 60%. You may also notice I agree with some parts, and disagree with others:
[post] by therealdeepsix
[posts] by cptsassrogers
[post] by phoenixgryphon
MCU Winter Soldier's Arm by shakespearesconesandstars
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