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An automail must be a masterpiece, as the user seems to be able to use it as a
fully working arm/leg/... It seems however, that it's no regular artificial
limb.

What's so special about an automail? How does it work? Are there any
drawbacks?


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fullmetal-alchemist-series
How does the automail work?


There's a pretty good description [here](http://fma.wikia.com/wiki/Automail).

To summarize it, automail is a prosthetic limb that connects directly to the
nervous system and requires no external power because it uses the electrical
signals from the brain as its power. They were originally created to be
weapons but then became sophisticated enough to use as a prosthetic limb.

There are a few major drawbacks to automail. The first is that it is
incredibly painful to install, as shown when Edward's automail is being
installed. The reason for that is that it is being connected directly to the
nerves, which send pain signals to the brain. The second is that they break.
Edward's has shown to break. They can be transmuted by the wearer, which is an
advantage because they can be changed into weapons and then back when needed,
but theoretically, they could also be transmuted by an enemy who could get
their hands on them.

Another drawback is that they are reliant on the person who is constructing
them. As shown by the time when Winry forgot a screw, if the person who
builds/installs it screws up, the automail can break or fall apart.

They can also conduct heat, being made of metal, so when it's very hot out,
they will irritate the skin because they'll become hot.

Automail can also be incredibly expensive. The God's Model automail (shown
below) has a price tag of 10,000,000 of whatever money they use.

![God's Model Automail](https://i.stack.imgur.com/IQghW.png)


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[@kuwaly](https://anime.stackexchange.com/users/93/kuwaly)'s
[answer](https://anime.stackexchange.com/a/3840/274) covered most of it, but
here's a bit more information as well.

> What's so special about an automail?

It's basically a prosthetic limb which has been optimized for fighting. Its
name comes from [auto-](http://en.wiktionary.org/wiki/auto-) (as in
"automotive") and [-mail](http://en.wikipedia.org/wiki/Mail_\(armour\))
(related to armor). They were originally designed to give more freedom of
motion to uses of prosthetics, but were soon fitted to combatants who had lost
limbs.

There is nothing extraordinarily special about these limbs except their
versatility and wide variety of uses. Additionally, this type of technology
did not exist in the real world during the time _Fullmetal Alchemist_ is set
(early 1900s).

> How does it work?

There are dozens of little parts to it, but it is largely composed of motors,
tubing, and the external metal covering. Here's a couple images of its
components (click to enlarge):

[![Shattered automail \(2003
anime\)](https://i.stack.imgur.com/SsSygm.jpg)](https://i.stack.imgur.com/SsSyg.jpg)
[![Shell-less automail \(2009
anime\)](https://i.stack.imgur.com/zqiTym.png)](https://i.stack.imgur.com/zqiTy.png)

It has no internal power source; it draws its power directly from the impulses
of the nervous system to run the intricate motors and other mechanics inside
it (and of course, to control which ones activate when). So, when the synapses
are sent, each part contracts with its motors, giving free, versatile
movement.

> Are there any drawbacks?

Of course--otherwise, why wouldn't people just cut off their limbs? ;)

kuwaly mentioned three major drawbacks:

  1. [It is painful to have installed](https://anime.stackexchange.com/a/5407/274) (nerve connections are painful--in real life, too).
  2. It is prone to breaking (just like a bone or limb).
  3. It creates a reliance on an automail mechanic for tuneups and fixes, and mechanics can make mistakes!

There are two drawbacks that weren't mentioned, though. One is that it is
quite painful during pressure changes; recall that when Ed went to the field
with Pinako to dig in the rain (2009 anime), he was actually forced into
vomiting due to the aching pain of the pressure system. The second is that the
material can work against you; iron and steel can cause issues like frostbite
when in cold areas, and are also quite heavy. (Some alloys alleviate this
issue, though.)


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I think an explanation can be that in the Fullmetal Alchemist universe, there
exist materials capable of converting neuron synapses (message signals from
the brain) into mechanical waves, which are received by the circuitry in the
automail and respond in its accordance. The automail limbs must be made to
function as a real limb and its machine parts are made to provide the same
contract and relax mechanisms as the muscles in our body.

It's just like in Inception with the dream-machine. Different universes,
different rules.


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