So I want robot enemies in my series, but I also want gore without killing living creatures (related to this, because the opponent is the same, the gr8 computer)

So basically the robots I talking about mimic human biology to some degree, more specifically they use a muscle-like tissue, that's stronger than it's natural counterpart, now this technique is used in all types of robots.

I proposed a few ideas for having liquids inside robots:

  • Liquid conductor

  • Required for the artificial muscle to work properly (might or might not overlap with the liquid conductor)


  • What could be the justifications for giving the fluid a red coloration?

Please consider using this (the robots employ composites of these to achieve the best possible combination)

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    $\begingroup$ Disney had a problem with early animatronics which used a red hydraulic fluid (fairly common), when they would leak it would look like the characters were bleeding. Many industrial lubricants are also bright red. $\endgroup$
    – John
    Commented Mar 12, 2017 at 17:00
  • $\begingroup$ @John You know, after the Fnaf franchise we all know that the supposed happiest place on earth is really just a mickey mouse murder house $\endgroup$ Commented Mar 12, 2017 at 17:10
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    $\begingroup$ Why in space do you even need to explain such stuff? More often than not such explanations only make the scene less believable. It's just red because who knows why. I don't care, but whoever cares may just go ask the Skynet directly, do you maggots understand? - Sir, yes, sir! $\endgroup$
    – Headcrab
    Commented Mar 13, 2017 at 6:32

9 Answers 9


You could have hydraulics. Hydraulic arms are routinely used in heavy machinery. In the first Terminator movie the Terminator was finally defeated by a hydraulic press. Hydraulic robots are real.

enter image description here

I googled up hydraulic fluid explosion and got this fine video. https://www.youtube.com/watch?v=4fD2Qm6xJ60

If that is not a jet of gore from a dying robot I don't know what is.

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    $\begingroup$ Hmm... high-pressure anime blood that's what I need. $\endgroup$ Commented Mar 11, 2017 at 20:31
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    $\begingroup$ The fluid is red because it's based on existing standards for transmission fluid (which is pink) or power steering fluid (which is red). From what I've seen, standard Mopar ATF+4 fluid is red so you can distinguish it from the other fluids in your car when a leak occurs. Personally, if you're going to do this, I'd want the robots to have a secondary (cooling?) fluid with the neon-green color of antifreeze. A Spurting green fluid is probably going to trigger as big an emotional response as a red one would. $\endgroup$
    – papidave
    Commented Mar 11, 2017 at 22:35
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    $\begingroup$ But why is it red? You should e.g. encorporate papidave's comments in your answer. $\endgroup$
    – JDługosz
    Commented Mar 12, 2017 at 20:55
  • $\begingroup$ I should have had something in there to start with but papidave came along with his improvement. I will leave them in his comment and up vote it. Credit where credit is due. $\endgroup$
    – Willk
    Commented Mar 12, 2017 at 21:21
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    $\begingroup$ @Will what if the comment is deleted, moved to chat, or otherwise disappears. $\endgroup$
    – minseong
    Commented Mar 12, 2017 at 23:01

The red could be a dye so a fluid leak would be visible and therefore easier to patch without taking the whole unit off line for diagnostics. An internal gauge might show a drop in fluid pressure, but wouldn't show where the damage has occurred.

  • $\begingroup$ It would be great if an android assassin can recollect his blood, so I have to find a way to quickly coagulate the blood. And if the recollection is not possible, then the dying can be used to get out of the scene before anyone realizing, that the thing that attacked the or what they attacked wasn't a living thing. Am I right? $\endgroup$ Commented Mar 11, 2017 at 16:57
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    $\begingroup$ Did you want the robots to be mistaken for organic at first? Or is the faux gore like a tongue-in-cheek splatter fest for the audience? $\endgroup$
    – wetcircuit
    Commented Mar 11, 2017 at 17:13
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    $\begingroup$ Both.and blood for the blood god. $\endgroup$ Commented Mar 11, 2017 at 17:22
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    $\begingroup$ +1. In Real World(TM) machinery, several of the fluids, especially the hydraulic fluids, are dyed so as to aid identification of a leak. The liquid handwavium that lubricates and/or actuates robot joints in RR's world is dyed red. Easy. $\endgroup$
    – cobaltduck
    Commented Mar 11, 2017 at 19:29

It could be for cooling down the robot.


The robot might have the liquid inside like computers do to cool it down. The enemies might have only cheap motors available and they need to cool them down regularly to prevent the robots from overheating. Also this might be useful for the good guys because when the robots are stabbed and they lose too much "blood" they won't be able to cool themselves down and will overheat. Here's a coolant for pcs that it could use:


Eco-friendly Anti-corrosive Solution Being non-toxic and non-flammable, the Coolant 1000 is an eco-friendly pre-mix solution with 2 years shelf life, providing great performance while preventing the entire cooling system – copper, brass, nickel, aluminum, and steel – from corrosion. In addition, users can easily refill by using the refill bottle.

  • Boiling Point: 210.2℉ (99℃)

  • Freezing Point: -4℉ (-20℃) Composition of Coolant 1000 as below:


From: http://www.thermaltake.com/products-model.aspx?id=C_00002609


This Japanese robot called the SCHAFT has a

"high-voltage and high-current liquid-cooled motor driver"

Further Research

For more info on coolants check out the wikipedia page: https://en.wikipedia.org/wiki/Coolant

This is the general definition:

A coolant is a fluid which flows through or around a device to prevent the device from overheating, transferring the heat produced by the device to other devices that either use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert, and neither causes nor promotes corrosion of the cooling system. Some applications also require the coolant to be an electrical insulator.

  • $\begingroup$ Hello and welcome to WorldBuilding.SE! Nice answer. Real life examples are always great! Do you have a link that you could reference where one could get more information about that robot? Would be a nice addition to your answer. $\endgroup$
    – Secespitus
    Commented Mar 11, 2017 at 23:25
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    $\begingroup$ @Secespitus I was going to add it but I can only have 2 :(. Here's the link if you could please edit it for me: spectrum.ieee.org/automaton/robotics/humanoids/… $\endgroup$ Commented Mar 11, 2017 at 23:26
  • $\begingroup$ I suggested an edit (you can only single-handedly edit something after you earned 2.000 reputation). Should be visible any minute ;) Thanks $\endgroup$
    – Secespitus
    Commented Mar 11, 2017 at 23:28
  • $\begingroup$ The OP is specifically asking for justification as to why the fluid is red, not (just) for why robots use fluids. $\endgroup$
    – JDługosz
    Commented Mar 12, 2017 at 20:56

An advanced robot using nanotechnology will be much more like a living tissue. It will naturally have circulatory fluid that can carry materials needed for the self-repair features, even if it’s not carrying fuel.

This is especially useful for the skin, which self-repairs heavy wear of the surface and the connective tissues that flex and stretch. So, they bleed when cut.

In my story, it looks like milk, being made up of tiny bits of various materials encapsulated in a membrane bearing tags describing its contents. But this becomes a commercial product with brands marketed to the sentient robots that need to use it. Adding to the reasons listed by others,

  • the color might be part of the brand recognition. Making it red like organic blood is a marketing tactic.
  • the proprietary formula for the encapsulating membranes may happen to turn out to be some color. This can be the natural color or dye can be used to make it more appealing, since it wasn’t bright white anymore and an “off” color could be perceiced as undesirable.
  • other substances dissolved in the water (not encapsulated in membranes) may be strongly colored, but are not there because they act as dyes.
  • smaller encapsulated nanospheres will start to have optical properties.
    gold particle size
    From Wikimedia commons: Solutions of gold nanoparticles of various sizes. The size difference causes the difference in colors.

The last is particularly elegant: the liquid is red because the nanoparticles it carries have a surface plasmon capability and the particle size is getting so small as to affect the resonance frequencies possible. For the cancer drugs pictured, “…These colors play a necessary role in the synthesis of AuNPs as indicators of reduction.”

So (the last reason), it’s not red because it has red stuff in it, but for deep physical reasons involving what makes it suitable for what it is.

  • It's red because it's artificially produced blood, and is made of hemoglobin. See--the human body is a machine, an efficient one, and it's a pretty good model. If the tech exists to create a person with a system that converts proteins which can carry oxygen throughout the body, it might look a lot like hemoglobin. Hell, it might BE hemoglobin. Your blood is red because, even though it's created, it IS blood.

You say:

Liquid conductor Required for the artificial muscle to work properly (might or might not overlap with the liquid conductor)

To which I say, yes, we have that too. It's called blood and it carries oxygen (fuel!) to our muscles so that they work properly.

You are calling it a "liquid conductor." I assume you mean electricity? That seems a bit...old tech to me. Besides, if it is a liquid conductor, when you stab one, mighten you receive a bit of an electric shock if this is so? Like stabbing a toaster and hitting the wiring or something.

But hey, guess what? Blood is a conductor of electricity! Mainly because is salty.

Here's a pretty indepth paper on what determines the conductivity. Click on where it says PDF to read it. The upshot is, they were trying to figure out a quick way to get a count on the number of red blood cells--and found that the higher the concentration, the higher the conductivity.


Modern technology is already blurring the line between organic and machine.

One solution: your robots use bio-batteries for power. Bio-batteries charge quickly through contact with any fluid that contains glucose. In other words, your robots look like they have blood because, essentially, they do. Losing too much of it will cause them to lose power and shut down, just like a living organism (though it will be possible to repair and refill them afterwards).

The robotic blood doesn't have to be red, but as wetcircuit's answer suggests, making it red would help engineers quickly spot leaks to repair them. The human eye is particularly good at picking out the color red.

The blood can also double as coolant. Actually, blood does have a secondary function as a cooling mechanism in living organisms, which is why people sometimes turn red when they exercise (blood flow increasing near the skin to radiate heat better). As Noah points out, liquid-cooled robots already exist.

Bio-batteries charge faster than conventional batteries, but they also (currently, at least) are not as good at holding that charge over long periods of time. Your robots may need to refuel (eat) on a regular basis to keep them ready for action.


Just have a general purpose "carrier fluid" - acting as fuel for a fuel cell, lubrication, coolant/waste movement, and hydraulic fluid. You could even have it conductive for "liquid"/"microfluidic" circuits.

This would greatly simplify logistics - since you would only need to stock a single type of fluid, and dump and change that periodically as needed.

You can handwave any characteristics you need (like hardening in oxygen in the absence of some inhibitor to be self sealing) on top of that.

  • $\begingroup$ You said nothing about why it has to be red, which is the actual question. $\endgroup$
    – JDługosz
    Commented Mar 12, 2017 at 20:57
  • $\begingroup$ Well, colour is entirely arbitrary. Standard hydraulic fluid is red, That said there's biological entities with non red blood too. $\endgroup$ Commented Mar 12, 2017 at 23:11
  • $\begingroup$ And yet, that's what he asked. «What could be the justifications for giving the fluid a red coloration?» not, “Why do they have fluid?” $\endgroup$
    – JDługosz
    Commented Mar 13, 2017 at 0:06

I know you're looking for robots, but have you considered using cyborgs instead?

You have a lot of latitude in deciding how much of the human is left, from RoboCop, who has just his brains, lungs, and possibly part of an arm left from his original, human body*, to someone who is fully human but has an implanted defibrillator.

I do understand from your question that you "want gore without killing living creatures;" depending on your implementation of cyborgism (?) and definition of life, that is possible. If something is >50% machine, is it human? More than 75%? What if the brain/mind is replaced by a computer?** A human body with a robotic or remote control brain will bleed, but will probably not be alive according to most definitions of death.***

* If I remember correctly. Here is some discussion on the original, though I have only seen the 2014 version.

** These are questions that can give a lot of depth to your work. If you want to integrate some philosophy in your work, you can raise or answer these questions in the story, either implicitly or explicitly.

*** Though of course many disagree with the definition of brain death as death, I'm pretty sure if the brain is completely removed, almost everyone will agree that the organism is gone.

  • $\begingroup$ Sorry, but what I want are strictly robots who adapted some biological features, either because they were effective or because of blending into human (or other) societies (in case of android assassins). $\endgroup$ Commented Mar 12, 2017 at 16:26

There are already experimental systems that delivery power to electronics, while also cooling them.

This allows the system to save volume, since both power and cooling are done by the same system.

The colour of this electronic blood could be red if it included things like copper or iron oxide. Copper seems more plausible, perhaps it helps with power transfer and/or the heat capacity of the fluid.

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    $\begingroup$ Welcome to the site, MffnMn. Note that the question is in regards to justifying the color of the "blood," not in justifying the existence of the system. You may want to edit your post to more accurately answer the question, else this may be deleted as inadequate. $\endgroup$
    – Frostfyre
    Commented Mar 12, 2017 at 18:19
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    $\begingroup$ This is interesting, could you explain more about it? $\endgroup$
    – kingledion
    Commented Mar 12, 2017 at 19:08
  • $\begingroup$ I think the linked article does a better job than I can, but the basic gist is to have a flow of charged battery fluid flow through your electronics; simultaneously supplying power and carrying away heat. The fluid then flows to some reservoir where it is recharged and cooled, before returning. $\endgroup$
    – MffnMn
    Commented Mar 12, 2017 at 19:21
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    $\begingroup$ @MffnMn The problem with links is that they can get out-of-date. This would leave an answer that relies on it meaningless, which is why we like elaborate answers that try to summarize the content of links provided. Links are welcome, but if an answer looks like a link-only-answer then it can be deleted, as if could potentially add nothing to the question once the link is out-dated. $\endgroup$
    – Secespitus
    Commented Mar 12, 2017 at 20:35

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