Vampires are the usual sort. They sleep in coffins during the day and awake when it gets dark. Apart from the normal ways of killing them, they are immortal and so, despite their thirst for blood, they will never starve to death.

Currently there is a plague of vampires and although they could be killed by the usual means, it is decided to try and make use of them.

The setup

A vampire lies in its coffin. When light ceases to leak in under the lid, the vampire awakes. It lifts the lid and sits up. However the lifting of the lid operates a mechanism such that, after a short delay, a bright light becomes visible. Seeing the lamp, the vampire quickly retreats back into the coffin and pulls the lid closed. This causes the light to be hidden. The sequence repeats indefinitely. A crank mechanism attached to the lid operates some machinery and so the vampire's ceaseless movement is converted into useful work.


There is no piped electricity or gas at this time, so lighting a lamp with a delay might be difficult to implement. Also, lamps bright enough to simulate daylight would be very hard to make.


There are plenty of vampires to experiment with and banks of coffins would be possible.

Vampires can survive under moonlight and when subjected to a dozen or so candles. Above this level, the brighter it is, the faster they move to avoid it.

Clockwork is well understood.

Please ask for clarifications before answering.


How should I design the setup to efficiently harness the movement of coffin lids? How does the lighting interact with the motion? Rough diagrams depicting the machinery will be welcomed.


I specifically want the power to come from the opening and closing of lids with vampires popping up and down. Mainly this is for dramatic effect. I'm not looking for radically different methods.

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    $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Feb 12, 2021 at 18:24
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    $\begingroup$ A light bright enough to scare a vampire will require vastly more energy than you can collect from the lid opening and closing. $\endgroup$ Feb 14, 2021 at 14:55
  • $\begingroup$ Vampires in your world have memory right? Any sane vampire might try to open the coffin a few dozen times, but once they realize that escape is impossible they are just going to stop trying, thus ending your attempt at creating a perpetual motion machine. $\endgroup$ Feb 14, 2021 at 18:17
  • $\begingroup$ @Outrageous Bacon - They are blood addicts, their need is so desperate after a while that they cannot stop themselves from checking "just in case". But, more importantly, as I mentioned somewhere else, sitting up is a reflex action prompted by darkness - they can't do anything about it. $\endgroup$ Feb 14, 2021 at 18:22
  • $\begingroup$ Re, "There is no piped electricity or gas at this time." Does that mean that the society has not yet developed an electrical grid, or does it mean that they do not even know how to generate electricity from mechanical work? $\endgroup$ Feb 14, 2021 at 20:11

9 Answers 9


This is a variation on abestrange's answer that allows for a more compact setup.

  1. Find a living author that is very popular worldwide.
  2. Vampirize them and put them on a coffin.
  3. Run a stake through the coffin so that it impales the vampire vertically. The stake connects to axles outside the coffin. Be careful to avoid the heart of the vampire, or use a metal stake to ensure you don't kill the vamp.
  4. Have an idiotic friend that has never read that author's works write plays based solely on their titles.

As seen in Dresden Codak.

An explanation on how to generate energy from dead authors: make their corpses spin in a thanatropic generator.

The equations for the thanatropic generator: Spin = Audience size times (author's renown + defamation of works) divided by skeleton weight

  • $\begingroup$ @chasly-supportsMonica you could always open the coffins remotely if you wish. $\endgroup$ Feb 11, 2021 at 18:21
  • $\begingroup$ In medieval times? $\endgroup$ Feb 11, 2021 at 19:22
  • $\begingroup$ @chasly-supportsMonica it all went anachronical when you included electrical lights. $\endgroup$ Feb 11, 2021 at 19:26
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    $\begingroup$ It would probably be easier to do with someone who represents some ideology very strongly. The classic example is to hook up a generator to Marx's coffin and then charge people money for the electricity its spinning generates $\endgroup$
    – Dragongeek
    Feb 14, 2021 at 9:40
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    $\begingroup$ @dragongeek Marx would be OK with that. Tesla OTOH did want electricity to be free and universal. $\endgroup$ Feb 14, 2021 at 14:52

The coffins should spin on axles

  1. The coffins should have as high a mass as possible to maximize the rotational energy gained by opening and closing the lid, but not so high that the vampire is unable to open it.
  2. When the vampire is asleep with the lid closed, the coffin should be upside down, when the lid opens this will rotate the entire coffin along with anything connected to the axle.
  3. Above the coffin, it will be well lit, either with daylight or other continuous light sufficient to cause the vampire to retreat and close the lid. But when the coffin is upside down, the light will not penetrate under the lid causing the vampire to awaken and open the lid again.
  4. The inertia of the coffin and axles will be calibrated to allow for the coffin to rotate to the down position after the lid is closed. Some experimentation will be needed to get the timing right.
  5. Flaps are installed to block any light getting to the lid while it is in the down position.

This arrangement solves the problem of switching the lights on and off, as the lights are on all the time, and daylight can be used when available.

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    $\begingroup$ Wouldn't the vampires fall out when upside-down? I can't quite understand how the gearing works either. Does this require a series of coffins like pistons in a car engine? $\endgroup$ Feb 11, 2021 at 19:19
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    $\begingroup$ Vampires are well known for being able to hang like bats, so should not fall out. $\endgroup$ Feb 12, 2021 at 10:50
  • $\begingroup$ A cage would work well enough to stop them falling out. $\endgroup$
    – Graham
    Feb 12, 2021 at 11:55
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    $\begingroup$ You're thinking of upside down vertically, the answer describes the coffin upside down horizontally (like rolling a log). When the lid is opened the coffin rotates on its axle like a rolling log. $\endgroup$
    – Touniouk
    Feb 12, 2021 at 14:08

It seems like coffin lids are perfectly shaped to be hooked up to bellows. That has the advantage of being a source of power your society might be familiar with. If nothing else it could be used to keep the forge's fires burning. Bonus points if they use it to power an organ.

Vampire Down

In this first image, the vampire is in the coffin, and the fires of the forge have gone down some. The vampire will then rise up:

Vampire Up

This collapses the bellows, blowing air on the fire for our blacksmith. As you pointed out in your comments, this also lightens the room, scaring the vampire back into their coffin. When the fires go down again, the room will dim and the process can repeat.

This can be scaled as needed by adding additional forges/coffins.

Just don't run out of forge fuel! Or, as others have said, make sure the lid can't open enough for the vampire to get out.

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    $\begingroup$ Great idea! Maybe the blowing of the bellows also causes the flame to flare up and brighten, thus automatically making more light and causing the vampire to retreat once more. This is definitely worth thinking about. It would also look and sound great. Son et lumière!!! How is your drawing ability? A diagram would be ideal. I'm even tempted to learn some animation software to show this in action. $\endgroup$ Feb 12, 2021 at 3:06

Chained vampire coffins. It takes a finite amount of time for a vampire to rise, so if you have each coffin close a flap exposing the next coffin to the light, you can generate any delay you like by adding sufficient vampires to the chain. Then for the last vampire, make it so that the flap is exposing the next coffin to the sun when the current one is not exposed, and you will have a metastable system of the vampires slowly rising in sequence. At this point you can use a slider crank linkage attached to each of the coffin doors to get a rotary motion.

  • $\begingroup$ This sounds good. Would it be possible to draw a rough diagram? I can't quite picture it. $\endgroup$ Feb 12, 2021 at 14:17

This is about the last way I'd use the vampires to create power, but if you do it this way you need your vampire to push on the lid of the coffin as hard as it can. Perhaps some prompting from behind would help, so let's have a little light inside the coffin to make it feel not so at home. Then a bigger light outside the coffin to return it. Both lights are powered from the same source, fed by a constant stream of acetylene from water dripping on a pile of calcium carbide, if you have that. Barring that, you tap into a mine with flashdamp.

Anyway, the gas flows into a bifurcated metal tube that contains a gutta-percha segment. When the coffin lid is closed, it compresses that segment enough that the gas flows faster down the smaller bore segment into the coffin, at which point the flame burning there bulges further out in a metal lantern housing until it becomes visible past an opaque barrier that otherwise blocks the vast majority of its light. When the lid is open, the gutta percha segment is released and a larger quantity of gas flows out into a similar lantern outside.

As for the lid itself, it serves as the escapement of an immense quality timepiece, the gearing of which permits its immense hour hand to exert prodigious force for lifting the monuments of your civilization on a predictable schedule, or more likely, for the purpose of periodically pulping the dissidents against your regime whom you have converted into vampires for final disposition.

enter image description here

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    $\begingroup$ "This is about the last way I'd use the vampires to create power" Yes, but just imagine visiting a vampire powered factory like this. Maybe even seeing vampire powered vehicles! $\endgroup$ Feb 11, 2021 at 23:30
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    $\begingroup$ Next up: powering a vehicle with brain flatulence. :) $\endgroup$ Feb 11, 2021 at 23:50
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    $\begingroup$ @Chasly: My preference would be for undead legal power. You set up a timeshare with two tenants who each own condominiums within a building. Those apartments don't actually have floors or ceilings at present, and the height at which each begins increases steadily with time. The vampire has been invited into the upper of the two apartments, not the lower... $\endgroup$ Feb 11, 2021 at 23:54
  • $\begingroup$ I did explore the flatulence idea to some extent a while back worldbuilding.stackexchange.com/questions/21271/… $\endgroup$ Feb 12, 2021 at 2:18

The setup is really simple.

enter image description here

The coffin simply has a lip that blocks light from leaking in until it is high enough, and a hinge so it falls back the right way.

A large array of such coffins can be arranged around a single bright light source. Lenses can also be used to increase the intensity (if not the total light), focusing on a peep-hole or notch that is exposed when the coffin lid lifts high enough.

Such lenses can use the light source more efficiently by wasting less of it on lighting the parts of the coffin that you don't care about, allowing more coffins to be controlled by one light source.

Experimentally you can determine the intensity of light in a crack required to make a vampire close the lid.

In the event of light failure, ensure that the hinged lids cannot actually open enough for the vampire to escape. When the light fails, the vampires will try, bash the lid against the top, and generate a horrible constant banging noise.

This results in a vampire engine that produces more noise when you throttle it down.

  • $\begingroup$ This looks very interesting. I think that it would run quite fast but with less overall movement than I had anticipated. It would cope well with a high gear ratio if I'm not mistaken. Might even be usable to drive a vehicle with a suitable gear box. $\endgroup$ Feb 12, 2021 at 21:49
  • $\begingroup$ P.S. I can see that altering the depth of the lip provides a great way of tuning the system. $\endgroup$ Feb 12, 2021 at 21:58

The most direct way to translate vampire-power into usable power is by getting them to rotate an axle. Have the vampires toil away inside a large hamster-wheel that drives a horizontal axle, or have a vertical axle that the vampires spin by pushing on spokes and walking around in circles.

The second one is how we harvested livestock-power to operate mills, the first was how we harvested the power of flowing water with water wheels (but the water ran on the outside, vampires will run on the inside).

Even if the vampires are magically tireless, they still get hungry. So only vampires that work get fed. If they refuse to work, then they remain locked in their dungeon without food until they do.

If they cannot be persuaded by the carrot, then threaten them with the stick. Not rotating the axle will cause a hatch in the ceiling to open, exposing them to sunlight.

Edit: Night time wouldn't be a problem either if we assume they don't much care for fire. A roaring fire next to / above the hatch would likely suffice to keep them motivated. You do not have to waste fuel keeping it going at all times, just when your mill decides to get lazy.

  • $\begingroup$ Vampires aren't zombies. They won't walk tirelessly in one direction. I specifically want the power to come from the lid opening and closing. Otherwise we're simply talking about slaves or beasts operating an ordinary treadmill. $\endgroup$ Feb 11, 2021 at 17:58
  • $\begingroup$ If the vampires won't walk tirelessly, why would they be able to open a coffin lid tirelessly? $\endgroup$
    – abestrange
    Feb 11, 2021 at 21:07
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    $\begingroup$ "If the vampires won't walk tirelessly" Have you ever tried to herd cats? It's not that they can't, it's that they won't. The coffin opening and closing is pure reflex that happens between waking and sleeping.. $\endgroup$ Feb 11, 2021 at 22:25
  • $\begingroup$ The same idea works for coffin lids. A vampire who doesn't make the hourly open-lid/close-lid quote gets shown a cross or something. I feel like reflexive sitting-up is The Undertaken from pro wrestling. Whatever he's supposed to be, it's not a vampire. $\endgroup$ Feb 12, 2021 at 3:10
  • $\begingroup$ @Owen Reynolds - Are vampires allergic to crosses - or is that just evil spirits? If so, a cross could be used to frighten them back into their coffin instead of a bright light.. $\endgroup$ Feb 12, 2021 at 15:03

My answer is I think a little mechanically simpler and more historically motivated than others, but forgive me if there is too much overlap with other solutions.

I'm going to highlight these two lines you wrote:

Also, lamps bright enough to simulate daylight would be very hard to make.


Vampires can survive under moonlight and when subjected to a dozen or so candles. Above this level, the brighter it is, the faster they move to avoid it.

I don't think that this first part is too big a deal. Since bright light sources are difficult, but the intensity of the light does not impact the effort the vampires put into opening the coffin, I would just try and harvest power from the opening of the coffin, not the closing.

My suggestion is to attach the hinge to a ratchet, such that the opening motion will drive a gear, but the closing motion will do nothing. This gives you a gear pointing upwards that intermittently rotates a quarter turn in one direction. Because its on a ratchet, its okay if the mechanism keeps rotating (due to other vampires, inertia, etc) because the ratchet will keep the motion from opening the door.

I would recommend using this gear in two ways. One would be to drive a timing mechanism that covers and uncovers a light at the maximum rate a vampire can sustain (remember that it can be relatively dim, so the bare minimum to make it retreat is fine).

The other would be to connect it to a speed reducer. I would also connect the entire bank of vampires to this reducer. Then, I would use that reducer to drive a pump or a lift. Based off of the time period you indicated, it would appear that the primary use for stationary engines would be along the lines of a pump or lift from removing water/materials from mines. ie James Watt's engine or its precursor the Newcomen engine.

If your vampires will use their arms to push the door open and closed, you could even strap them into the coffins around their chests. That way you could make relatively compact bundles of coffins and time them with a 1/4 offset to get continuous power output from a shaft that runs through the centre of the bundle, and then you could orient the bundle however you wanted. You could use this to drive handcars, etc.

Finally, you said that they never tire, so you may not care about thermodynamic accuracy, but the easiest way to use them if you do decide to would probably just be to burn them, rather than reloading coffins over and over again.


Simple Lightsource: The Sun!

Perhaps this system can be simplified significantly if the energy is only harvested in the daylight. Either use a system of mirrors and a trigger correlated (and delayed) with the opening of the lid to allow light into the room, or simply tie the lid to a larger door in the ceiling. At night, simply go around and lock all of the closed lids. I like the element of risk this poses: reminds me of nuclear power plants. You're playing with a dangerous energy source, and so there's a risk that if your attendants don't properly manage it, a "meltdown" (read: prison break) might occur!

Think about solar power: you don't get anything at night. You store the energy! In point of fact, the largest battery holding solar energy in the world is nothing but a giant man-made lake! The energy harvested goes into lifting water into the raised lake. When you want to take energy out, you allow the water to flow downhill and turn a turbine. Easy-peasy, especially for your clockwork-savy folk.

My thinking about harvesting the energy from the coffin lids:

  • It's likely simplest to harvest the energy from the lids as they fall rather than as they rise. Think about a pulley turning a crank with a one-way ratchet (like the rear gears on a bicycle or a ratcheting socket wrench [Edit: Just saw Mike Serfas had the ratchet already.]) and freeweight so it is unconstrained when being lifted. The line stays taught when the coffin is being lowered due to the freeweight, lifted again when the axel turns the other way.
  • People are right about heavy lids. Gravitational potential energy is $P = mgh$, with m - mass, h - height, and g - gravitational constant. Things are slightly more difficult to calculate precisely if the object is rigid, extended, and rotating, but the principle is the same. This is the same principle by which the aforementioned lake stores its energy.
  • If you want to get technical, you can consider the size of your pulley: this might make things easier efficiency-wise if you need a large amount of torque in the immediate application. Bigger pulley = more torque. The same thing can be applied through a series of gears with varying ratios between the number of teeth, but then you're losing some extra energy in friction.

Source: Physics PhD student who clicked a cool sounding link on the side of Math StackExchange...

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    $\begingroup$ I would argue that the largest battery holding solar energy in the world are the 200 years worth of usage of coal stored underground $\endgroup$
    – L.Dutch
    Feb 12, 2021 at 5:19
  • $\begingroup$ I was simply going off of man-made purpose-built batteries. If you want to play it that way, I would argue that the largest battery storing solar energy in the world is just the ocean. By a quick Google, that's 1.332 Yottagrams (Yg) of seawater. Average temperature is about 273-276 Kelvin. Call it 273. Specific heat capacity of seawater: 3.991 kJ/Yg*K => 1.451E+24 kJ, vs 2.6E+19 kJ for the entire world's coal reserves. Even if you expand your concept, that's vs 3.9E+19 kJ for the entire world's fossil fuel supply (Data 2003 estimates, See: WolframAlpha). --Or it's just the whole planet. $\endgroup$
    – Jopacabra
    Feb 13, 2021 at 6:29
  • $\begingroup$ The thing is, the water on Earth came via asteroid bombardment during the Hadean era en.wikipedia.org/wiki/Hadean, unlike coal, which is literally fossilized sunlight, easy to acquire, burns in air, etc. Not sure it's anywhere near as easy to make use of the energy in the ocean. $\endgroup$
    – chiggsy
    Feb 13, 2021 at 15:30

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