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I’m writing a steampunk/weird west story set in 1867 and I want to incorporate some form of armored battle “walkers” (aka mechs). Looking for ideas for powertrains that could conceivably run such a vehicle.

I’m okay with being somewhat anachronistic, although I think something like a diesel engine might be too much.

Steam is the obvious answer for the setting, but I’d like to go a little deeper in explaining the tech than “it’s a steam-powered mech.” Curious about specific examples of steam engines that would be suitable for such a platform, or alternative power sources (internal-combustion? clockworks? hybrid-electrical?).

This is a pulpy story so it doesn’t have to be too realistic, but I’d rather not have someone with basic engineering knowledge (which I don’t have) throw the book across the room in a fit of disgust.

The vehicles I’m envisioning are designed to replace horses in cavalry regiments, so they can’t be too plodding. They’d be used for scouting and shock attacks. Agile and fast would be ideal.

Would love to hear your thoughts!

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    $\begingroup$ There's a bunch of steam stuff on my profile. Feel free to browse :) Also have a look at the search function. E.g. "steam is:q" will show you all questions that have the word steam in them. $\endgroup$ – dot_Sp0T Apr 17 at 8:02
  • $\begingroup$ Keep in mind that there were many types of cavalry throughout history. You'll need very different designs if you want to replace light cavalry (or just horses that scout, send messages, serve as transportation) than for heavy cavalry that plow through infantry. $\endgroup$ – Blueriver Apr 17 at 14:57
  • $\begingroup$ I hate to bring this up as an example because it was a terrible movie, but have you seen the Will Smith Wild Wild West movie? The climactic battle took place on a giant, steam-powered, walking mechanical spider. (Which, according to Kevin Smith, was a leftover from the cancelled Nick Cage Superman movie - great story that everyone should listen to at some point.) $\endgroup$ – Darrel Hoffman Apr 17 at 15:30
  • $\begingroup$ @Blueriver These vehicles are designed principally for troops in the Western Territories, so would be designed for scouting and dealing with native uprisings. $\endgroup$ – Ryan Williamson Apr 17 at 16:24
  • $\begingroup$ @DarrelHoffman I did see that movie! $\endgroup$ – Ryan Williamson Apr 17 at 16:24
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A steam tractor might not be a bad solution to your query.

Your time frame is only a couple decades in advance of the diesel motor, and is only about 10 years in advance of the time Diesel was coming up with the idea for his kind of motor.

Though I'd forget about walking. That kind of tech is something we haven't even really perfected by the 21st century! At that time, a wheeled mecha shouldn't be too difficult to work on.

A steam tractor is basically built like a tank, and is almost the size of a tank. Just put some armor on it and a couple gatling gun turrets and you'll have a wonderful and terrible land ironclad to send into battle!

enter image description here

They aren't really built for speed, but are pretty powerful. For your armies, such vehicles could be adapted for a little more speed, after all, steam locomotives were pulling trains in excess of 60mph a couple decades before.

Main drawback in the design is their horrific steering mechanism. That's something your engineers will work on!


Another possibility, with considerable suspension of disbelief, is the marriage of steam power with the walking truck.

The walking truck was developped in the mid 20th century, and as you can see is quite wobbly and difficult to manoeuvre. Nevertheless, a couple steam stacks and a few gatling gun turrets and you're on your way!

enter image description here

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    $\begingroup$ Not a bad idea, although I’m pretty darn committed to walkers...realizing of course that it will require some suspension of disbelief on the part of the reader. It’s one reason I’d like to be more authentic with the power plant, since a legged vehicle in 1867 is admittedly ridiculous. But also awesome. $\endgroup$ – Ryan Williamson Apr 17 at 2:16
  • $\begingroup$ @RyanWilliamson -- Understandable! I think it's more a matter of reality check failure. But as you say ... suspension of disbelief! $\endgroup$ – elemtilas Apr 17 at 2:27
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    $\begingroup$ As far as stability and whatnot, if you can build a spider walker (legs out rather than straight down), that will be a lot more stable. (It's all about having a wide stance and low center of gravity. Keeping low also makes you less of a target!) Combine with six or eight legs that "rest" at equally spaced points on a circle and a rotating turret, and turning becomes a non-issue; you never turn the legs, because they can "walk" in any direction. $\endgroup$ – Matthew Apr 17 at 14:16
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    $\begingroup$ @RyanWilliamson, yup, bipedal walkers are utterly impractical, and I'm not entirely convinced they're even inherently "cooler" than other kinds. BTW, strongly recommended viewing: Wild, Wild West, which features... exactly what you're trying to build, I think, or at least very, very close: a walking, steam-powered engine of destruction 😉. $\endgroup$ – Matthew Apr 17 at 16:50
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    $\begingroup$ It makes sense to focus on the engine rather than the legs. Anyone can imagine legs, anyone can imagine a Mech, but if you have to fight with a Mech in wild-west era it might be useful to know how they are powered for story reasons. And like the upcoming game "Iron Harvest" few people will go "hang on why legs though?". You define the world to have something (the Force, Magic, sound in space, Elemental Bending, a Prophecy, humans still relevant despite advanced AI, Steampunk gadgets etc) and as long as it fits the narative and the lore people will accept it. $\endgroup$ – Demigan Apr 17 at 17:04
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Dynamite boots.

If you want to walk, have a human do the walking. Then augment him.

Start with Rocket Boots.

rocket boots https://www.nytimes.com/2007/03/17/business/worldbusiness/17gazshoes.html

The dream Mr. Gordeyev conceived in 1974 to run faster and jump higher without getting tired might never have become a popular option for commuters or even caught on as a sport. But unlike the Segway, the American-invented self-balancing scooter, it never had a chance.

Instead, the boots became a military secret, as generals envisioned soldiers running swiftly and effortlessly alongside armored vehicles.

Rocket boots are already a little bit like stilts. Your mech suits have rocket boots with longer legs and a longer stride.

But it is 1867! What is the hip new tech?

That's right. Dynamite!

https://en.wikipedia.org/wiki/Nitroglycerin

Liquid nitroglycerin was widely banned elsewhere, as well, and these legal restrictions led to Alfred Nobel and his company's developing dynamite in 1867. This was made by mixing nitroglycerin with diatomaceous earth...

The inventor Nobel teams up with your mechsmiths to make rocket boot stilts powered by tiny pieces of dynamite. It helps that nitroglycerine is a contact explosive. The downstroke of the stilt piston leads to a mighty upstroke, propelling the leg up. An automatic feed mechanisms feeds Nobel chips to the piston in a rate proportional to the stride. One piston at a time for a run, and a double chip in both pistons at once for a mighty trench-clearing jump.

Your armored infantry in the dynamite boots are tireless and faster than horses, although they are not going to sneak up on anyone. Their true forte is hand to hand combat. It is not just boots - the upper body armor also has dynamite-boot powered pistons augmenting the arms and armored gloves with brass knuckles braced to the arm; they can punch a hole through a stone wall then pick up a cannon and throw it.


This has become more power armor than steam mecha but I really love the dynamite power angle for 1867 technological wonders. And to my knowledge, dynamite powered bionic iron knights have never been done!

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  • $\begingroup$ That’s pretty darn awesome! $\endgroup$ – Ryan Williamson Apr 17 at 3:19
  • $\begingroup$ As a minor problem to handwave, I wouldn't like my femurs being driven into my lungs through my pelvis by the hypersonic detonation of nitroglycerine (at 30 Mach). Maybe use something that deflagrate. Besides, on a repeated use, the rocket boots will need to support temperatures in excess of 3,422C, the melting point of tungsten. $\endgroup$ – Adrian Colomitchi Apr 17 at 3:21
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    $\begingroup$ @AdrianColomitchi - I propose for this application shock absorber type pistons to more smoothly convert the energy. Of course there will be radiator fins to deal with waste heat, and a steam jacket - on prolonged use the iron infantry will steam. $\endgroup$ – Willk Apr 17 at 12:15
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    $\begingroup$ This could also be steam powered. Instead of the mechanical actuation detonating an explosive, it could open a valve to fill the piston with steam. STeam may be more style-appropriate, as well as easier to manage than explosives (though it could still explode) $\endgroup$ – BillThePlatypus Apr 17 at 15:31
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    $\begingroup$ Springs absorb shock and release the energy over a longer time, so that would work. (And you'd have a very steam-punky springs-on-cylinders army.) Also, "dynamite chips" is spot on, it's a very small explosion. You'd have to do a lot of detail work to determine how this could be strapped to arms and legs without breaking them; I suppose it will be more like exoskeletons where the human muscles provide steering and control and the dynamite provides power. $\endgroup$ – toolforger Apr 18 at 5:27
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Expansion cylinders and external combustion is almost a no-go for speedy nimble walkers. The pressure requirements will impose large weights and large weights on "feet" means almost guaranteed walkers sinking into soil (except for stony/large gravel soils).

For reduced weights, you may get around handwaving precision mechanics and the use of alcohol burning inside high speed gas mini-turbines.

Steam turbines were invented 1880-ies, big, bulky and powerful - gas turbines have a much early history - 1629 as the first industrial applications the handwaving only requires the miniaturisation and serious step-down transmission to pay for reduced weight and power in the kW range (1HP = 745W).

An example of a school project axial turbine - the end shows the "death" of the turbine due to meltdown of bearing supports (i.e it didn't explode even if the housing was made from food tin cans)

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I came up with a solution to this for a tabletop RPG homebrew some years ago.

Quite simply, the mech's limbs used hydraulic actuators as muscles, and its power source provided torque to a hydraulic pump.

The pilot would be suspended in the cockpit, strapped into a frame or anchored to a frame that engages with sockets in their form-fitting plate armour, the movement of the frame causing the mech to mimic the movement of the pilot.

The power source varied. Some mecha used a diesel radial engine to drive the hydraulic pump (a radial engine is wide and flat, and leaves more room in the torso for the cockpit). However, endurance was limited to around a day of activity before they had to be refueled.

I also came up with a couple of atomic power sources that relied upon the magical nature of my world. They would provide years of endurance, but were considerably more expensive than a radial engine and a supply of diesel fuel that would last an equivalent duration.

One was Tremium, a hard, brittle greenish metallic element. When it fissioned, it would release some heat, and a burst of kinetic energy in a random direction, unless there was a sufficiently powerful magnetic field nearby, in which case, the kinetic burst would be directed along the magnetic lines of force. The kinetic burst also increased the liklihood of neighbouring Tremium atoms to fission. By putting Tremium and magnets around the edge of a stack of flywheels, and arranging a governor mechanism to control the gap between flywheels proportional to the speed of the flywheel stack, a self-regulating reaction could be sustained, and controlled by altering the governor setting. In the event of governor failure due to battle damage, the flywheel "pancakes" could collapse together, resulting in a runaway reaction that might either melt down the reactor, or result in the flywheels exploding due to a purely mechanical failure of their structure, or heat demagnetisation of the permanent magnets next to the Tremium on the flywheel rim leading to chaotic, rather than directed, energy release. Despite its more favourable properties as a kinetic power source, Tremium was particularly hazardous to human health if not stored properly. If Tremium dust was inhaled, its spontaneous decay would slowly but surely tear apart its victim's lungs... and the brittle nature of both it and its ore meant that chaotic decay was highly likely to cause fractures and release dust. It was commonly stored in either magnetized containers in small quantities, or in wax-filled containers.

The other atomic power source was an element called Fulminium, an orange crystalline substance with semiconductive and piezoelectric properties. When it decayed, it would emit some heat, light in the orange and ultraviolet frequency ranges, and electrons, and by compressing the crystals between conductive plates of dissimilar metals, a direct electrical current could be tapped. Fulminium was stimulated to decay by ultraviolet light. A reaction could be regulated by placing a crystal in a chamber with reflective walls and movable black shutters; by controlling the shutters, the reaction could be controlled. In mecha, that electrical current could be used to power electric motors, which would drive the hydraulic pump. Fulminium was a somewhat more risky substance to use, as its decay products were opaque, and as a reactor crystal aged, it became increasingly more likely that the impurities would absorb some of the light energy and convert it into heat, to the point where the crystal would explode. This led to fairly frequent reprocessing of Fulminium reactor crystals to extract the impurities. It was considerably safer to mine Fulminium ore than Tremium ore, though occasionally electrical charges would build up to the point where they would emit bolts of lightning, unless the ore vein was grounded.

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Steam, the actual actutators moving the limbs are steam cylinders. I'd go for a closed system that does not constantly loose steam/water (so unlike contemporary locomotives). This means you need large radiators as condensors, and sumps equipped with small pumps at the lowest points.

For a control system I imagine one operator per limb fiddling with many large levers to operate steam flow, plus one "conductor" who oversees the whole.

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Fuel Cell + Electric Motor

The first fuel cell came in 1838, and fuel cell technology doesn't really require much in the way of supporting tech - those early fuel cells were conceptually almost identical to modern phosphoric acid fuel cells. The only hand-wavium you really need for your story is an efficient catalyst and some improvement in electrode life. These fuel cells also generated a lot of heat and steam, so they'll fit your steampunk vibe just fine.

DC electric motors date to the same era (1827) and require no hand-wavium at all - by 1837 electric machine tools and printing presses were designed (they failed to catch on for the lack of a power grid to supply them.)

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  • $\begingroup$ Oh that’s very interesting. I was thinking of perhaps a combination of multi-expansion steam engines with batteries of clockwork springs to capture surplus energy and “save” it for when bursts of power were needed. $\endgroup$ – Ryan Williamson Apr 17 at 16:28
  • $\begingroup$ I like the idea of fuel cells a lot. Apparently the risk of exploding fuel tanks is also relatively low due to how fast the hydrogen vents out of a puncture (say from a bullet). $\endgroup$ – Ryan Williamson Apr 18 at 1:30
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Maybe the walkers have a flywheel which rotates very fast and, through some fancy shiny gearbox, delivers energy to the walking mechanism. It could probably not last for longer missions (in a believable way) and it would need to "refuel" at a big steam powered recharging station which would take a minute to spin up the wheel back to its operational "ludicrous speed".

https://en.wikipedia.org/wiki/Flywheel_energy_storage

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  • $\begingroup$ Can’t ever go wrong with ludicrous speed. $\endgroup$ – Ryan Williamson Apr 17 at 16:35

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