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As we all know, the idea of any sort of legged fighting vehicle would be a horrible idea in real life, as mechanical complexity and the huge silhouette would make them punching bags for just about any weapon system. But we are still infatuated with the idea of them in fiction anyway.

Note, mecha here in question a rather broad definition, which can be anywhere from overgrown powered armor the height of a single-story building to multi-story-tall war machines that weigh more than tanks.

So what kind of technology or change in warfighting environment would be needed for the mecha to be a viable weapon system, and at what scale should these mecha be (i.e. really over-sized infantry, tank-sized, or buildings on legs)? Or is weaponizing legged vehicles a lost cause? Assume that any technology introduced could be applied to all fighting vehicles.

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    $\begingroup$ Why is the US Army developing a robot pack animal with 4 legs? If you read up on that, it may inspire you with the real reasons they are built. $\endgroup$ – JDługosz Dec 6 '15 at 9:27
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    $\begingroup$ Related: worldbuilding.stackexchange.com/questions/10320/… $\endgroup$ – Dan Smolinske Dec 7 '15 at 7:40
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    $\begingroup$ Legged war machines have a great number of disadvantages over wheeled ones. So, in short: To make someone still choose them, their advantages must outweigh the disadvantages. That will most likely boil down to terrain that cannot be navigated on wheels. $\endgroup$ – Burki Dec 7 '15 at 14:04
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    $\begingroup$ If you can get them to jump, you're all set $\endgroup$ – Nahshon paz Dec 7 '15 at 14:51
  • $\begingroup$ Check out "Atlas", he's pretty sweet, kinda' drunk but has a good start! theguardian.com/technology/video/2015/aug/18/… $\endgroup$ – Timmy Dec 7 '15 at 18:35

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Battletech justified mechs by describing them as significantly superior to wheeled vehicles - they carried more/better armor, were more agile, and carried more weapons than a tank of the same weight. The simplest solution is hand-waving.

While the 30 foot tall giant mech is impractical, a power-suit/exoskeleton/armored infantry -such as battletech's elementals,or the battle-suits of the starship trooper novel - make sense. They would be somewhat larger than a human being, however not so big that they would become walking targets. They would enhance the wearer's strength, agility and firepower, which are big concerns in the military today (the US army is experimenting with all sorts of exoskeletons ATM).

They would be deadly against infantry - you're basically fighting a brick wall, as well as deadly against tanks, since they can carry powerful weapons that a typical infantryman could not. Imagine stabilized, computer-aimed, dual wielded machine guns. Or even a small mini-gun, with a lot of ammo.

Interestingly a donkey type of mech would be a useful counter-part to armored infantry. Donkeys can haul heavy gear to places where most vehicles cannot. A mech version would be able to keep up with the mech infantry, and carry supplies such as extra ammo or batteries for them. Its not a bit stretch to imagine these mounting weapons such as mortars, light anti tank rockets, or heavy machine-guns to lay down suppresive fire.

I'm also a big fan of the tachikoma from the GITS Stand alone complex universe. They're spider-bots capable of turning on their own axis, and can - optionally - be piloted from a pod on their thorax. While not walkers in the two legged sense, the arachnid design worked well: they were stealthy (even without active camouflage), and could move in tight spaces. Something like that, while slightly larger than a man, would have better firepower than poor bloody infantry, and go places where a big honking tank cannot.

Finally a walker with the same size/armament as a modern tank, might have the advantage of being able to go 'hull up/hull down' more effectively. A tank that can lift itself over a berm, pop up to fire at their target, then sink down behind cover, and adjust for terrain being uneven would be useful. This would more likely take the form of a 'tank with legs' rather than a 'giant humanoid robot' (imagine a turret on a body with 4-6 legs). The justification for the development of such a vehicle would be easy: better ability to adapt to terrain, especially in urban rubble scenarios (it could just pick its way through the rubble).

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  • $\begingroup$ Mandatory link to the "Big Dog" donkey type mech which is developped IRL: youtube.com/watch?v=cNZPRsrwumQ $\endgroup$ – fgysin Dec 7 '15 at 7:36
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    $\begingroup$ The only downside of a mech ducking for cover is that it's very unlikely you'll find something that provides more cover than your own armor plating. It's like hiding a tank behind a brick wall; anything that's going to be capable of harming a tank will go straight through the wall as well. (This is also my main gripe with a bunch of videogames that allow infantry in powersuits to take cover behind car doors. Looking at you, XCOM.) $\endgroup$ – Erik Dec 7 '15 at 14:54
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    $\begingroup$ I was thinking big earth berms, like real tanks. You'd be surprised how shell-resistant a few feet of packed earth is. Think sandbags, but bigger. $\endgroup$ – Journeyman Geek Dec 9 '15 at 2:52
  • $\begingroup$ Fallout's Power Armor comes to mind $\endgroup$ – T. Sar Dec 14 '15 at 19:49
  • $\begingroup$ More armor is a losing claim ever single time. The surface area to volume ratio disparity is all she wrote on that. What ever technology you use on the mech can be used to better effect on a tank. And we haven't even looked at the ground contact pressure question yet. $\endgroup$ – dmckee May 21 '16 at 2:55
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1- As o.m. suggested, use in areas of uneven terrain and no smooth roads.

2- Using such war machines against people living in medieval or earlier peoples would give you a huge bonus of awe and fear (if you paint your war machines accordingly to make them look like monstrous spiders) which mechanical tanks and trucks etc would not have.

3- If in post-modern, futuristic settings, such machines come with the advantage of being more concealable (more so if you can make them flexible enough to be folded into a box or ball shape that mimics a rock or log).

4- Again in post-modern settings, such machines would be highly preferred over tanks and other recent military vehicles when you consider automatic, AI-controlled seek and destroy machines that are programmed to clear an area of all personnel (civilian and military alike). While tanks and other such things would have a hard time going from human to AI-control (think about all the navigation and gear change and turret direction change algorithm and whatnot), such machines (with mini-cameras fitted in all 4 directions) would be able to see further (due to being higher) and be more accurate.

5- As for the height, it would have to be as little as possible for obvious reasons of practicality. If I were the lead designer/engineer, I would prefer 8-10 feet tall machines with 6 equally spaced legs. On smooth surfaces, the machine would travel by rolling on the wheels (all legs end up in wheels) while walking-like mode of locomotion would be used only in uneven terrains and for crossing barriers such as walls.

6- As for the weapons, use something which does not require rapid reloading/refilling. I would consider using high energy batteries and using laser rays as primary weapon. In case of being overwhelmed by enemy soldiers and unable to escape, the machine would be able to self destruct with a huge explosion, so as to take it's enemies with it.

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    $\begingroup$ Honestly, in medieval times even a Mini Cooper would give you a significant bonus of awe and fear. :P $\endgroup$ – fgysin Dec 7 '15 at 7:40
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    $\begingroup$ I'm not sure I get your point 4. Tracked vehicles are extremely easy for AI to drive. Shifting gears and steering is much more simple than walking from an electronics design perspective. That's part of why we have a lot of reasonable successful self-driving car-like vehicles, and very few autonomous walkers. $\endgroup$ – Deolater Dec 7 '15 at 15:10
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    $\begingroup$ About your point 4: It is not easier to program the motion of a legged creature. On the contrary, wheeled and tracked vehicles are a lot easier to program ( just count the degrees of freedom ) $\endgroup$ – Burki Dec 7 '15 at 15:11
  • $\begingroup$ I have to agree on that. I guess tanks and armored AI controlled vehicles would indeed travel more smoothly and make decisions quickly, But the ease of aiming and shooting you get with a laser-gun mounted at 8 feet height is worth the pain of 6 legged locomotion algorithms :p Plus, notice that on smooth surfaces the thing would move on wheels just like wheeled vehicles and the treading locomotion would be used only in uneven terrain. $\endgroup$ – Youstay Igo Dec 8 '15 at 3:35
  • $\begingroup$ Why would a legged vehicle be more frightening to medieval people than a tracked vehicle? I doubt that either would be viewed as a monster or supernatural: people built large ships and siege engines in ancient times. They were well aware of the idea of big machines. It's popular to suppose that ancient or medieval would be awed by modern technology in the sense of saying "it must be a demon!" But there's no record of anyone seeing a large enemy ship or siege engine and assuming it was supernatural. They just understood that the enemy could make bigger weapons than they could. $\endgroup$ – Jay Dec 14 '15 at 20:04
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  • Instead of bipedal mecha, think multi-legged spiders. That means you get legs, but a relatively low profile as well.
  • Fight in areas with few roads and very broken terrain, so that half a dozen legs are superior to a pair of tracks. The walker can climb over broken trees, boulders, etc.
  • One big main gun in a turret, not multiple smaller guns in the arms. Possibly no arms at all.
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Don't just think mechanical spiders, but real ones. If the machine is compact enough and has advanced gripping "feet" it can climb 3 dimensional surfaces, going up walls, down shafts and in other places that people and normal fighting machines are unable to.

IF the machine is small enough it can move forward and act as a scout, secure flanks and provide security in virtually all situations. A bit bigger and it can start carrying weapons, providing the enemy with a more difficult problem (small robotic fighting machines coming at them from 3 dimensions).

The same principle applies to a certain extent with bigger machines, up until it becomes difficult for them to either stay attached to walls or hide in corners. Larger machines can carry more weapons or ammunition, and have the option of carrying heavier calibre weapons. Carrying automatic cannons or grenade launchers allows you to take on bigger and harder targets than a smaller machine with light machine guns.

My own opinion is that the humans will be directing the fight (maybe protected in a suit of powered armour) rather than doing the fighting on their own. YMMV

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I only choose to answer, because this is not a comment I'm afraid of... Well, after looking over all of the other answers, I think you might miss a thing that pretty few people take in account when thinking about their "superior" battle-mechs. Okay, mico villena noticed this kind of (the role), but I can't see anyone who cared about the question so what happens to my mecha when it got hit?

To keep the advantages of multi-pedal... traction, that thing should not get to heavy. And speaking of weight, it needs to be symmetrical and keep all the heavy stuff close to its center to avoid just tipping over when the walking ground is uneasy. Or sinking in. Tracks do spread weight pretty great... but I just need to remember my fat cat with its tiny feet walking over my belly... ouch.

So you can't use the same grade of armor you can plaster on a tank. These guys are flat and... well, they can tip over in heavy terrain too, but you have a pretty predictable surface thats exposed to attacks. Stack all your armor, hard- and softkill systems there and you get protection at a level no mech could reach.

So whats about the hitting stuff? Now compare your flat tank and a high walker. Let both of them get hit by a kinetic penetrator. Even if your walkers armor is (in theory) able to defect this, the sheer force will knock it off balance or even remove a leg. Or a plain old artillery shell, that a tank won't notice as long as its not a direct hit with a bunker breaker concrete shell, might knock over your walker too thanks to its blast force. Maybe it can stand up again, maybe it break some components during its fall... But, yeah, a tank can get stuck in a shell bast hole, but that need bad circumstances or a driver daydreaming.

These mechs would need to... crouch to get their center of mass down, which means that they need to know that the attack is incoming. Event then it may take some time.

But to be honest... there is one thing they may excel in: avoid anti tank rockets. You see these things coming all the way? Just step aside just a split second before impact!

Your question... as long as you do not want to use them as a replacement for tanks, they will find a niche. And for some reason I opt for small bots that are used for urban combat. Just drop a few dozen of 'em at a building crawling with enemies. Bonus points for integrated C4 Explosives, all kind of sensors you can think of and silent weapons. Make them water-proof and they may enter that building from bottom up. Oh... nice toys. And the good old exosceletons of course. For impressions google terminator space marines

But really big ones? You may add a flag and a disco-light to them, that wouldn't make them more vulnerable at a modern battlefield. Their time will come, when you change kinetic and blast force as your damaging force for lasers and stuff that does not push.

EDIT: Oh, I forgot: what does have lags, can stumble...

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There was a lengthy discussion of this on the Phoenix Command Combat System mailing list in April of 2003. It's a public yahoo group so the archive of the lengthy discussion is available.

The digest version is this: Way cool, lots of fun but terrible in real life.

Ground pressure is problematic. Barring very big feet mechs will sink deep enough to make balance and walking difficult when all the weight is shifted to one foot to step. Multi-legged designs could alleviate this.

The humanoid format presents a huge target area by essentially standing a main battle tank on its end and forcing the builders to armor a far larger area. A multi-legged format could alleviate this as well, but the elevated under belly is either a very vulnerable target or requires a larger surface be armored.

Balance and control systems become hugely complex and the time, expense and technical requirements of maintenance and support make mechs far more difficult and expensive to field.

A shoulder launched anti-tank missile can be hell on a main battle tank's side armor. Imagine this applied to the side or back of a mech's leg.

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As have been mentioned, mechas are heavy. And even tracked vehicles (tanks) can handle fairly rough terrain.

So what you'll have to have is terrain that is too rough for tanks (think the fjords), and improbably dense (maybe mostly basalt? granite? actually metallic?) so that leveling the terrain is cost prohibitive (otherwise you'll just drive some bulldozers around).

You're also going to want to decrease gravity so they're not quite so ungainly, but enough gravity that stuff will actually stick to the surface. What it sounds like then, is that your mecha will be most suited to large asteroid/small planet sized bodies. Think maybe the moon, but a lot worse terrain.

Now having a legged spider-like vehicle begins to make a lot of sense. It can easily traverse weird terrain, moving directly vertical if there are fissures in the rock that it can grasp, or even hanging inverted, if everything holds.

It may be easiest to hand wave at the terrain and say, "Magic!" but there are real places on earth where you could find some similar terrain. If you magic up the conditions to create those sorts of conditions, it's possible that mecha could be worthwhile. One thing to note - eventually if the place is valuable enough, we'll figure out a way to mine it, flatten it, dig it up, or whatever it is we need to do. So eventually the mecha will be replaced by something cheaper. One answer for that, though, is to make the terrain mostly something garbage that nobody cares about, but with certain smaller pockets of valuable Unobtanium. Then you'll have your mechas, drop them, fight for and mine the resources, then move on to the next location. That way you constantly have a reason for mecha.

Probably the only way to have that happen to Earth, though, is to destroy the terrain with meteorites that are made of such a material and size that we cannot easily remove, and enough of them that they completely alter the terrain. This, of course, kills pretty much all life on Earth in any scenario I can imagine, so the only reason to come back would be either for nostalgia, or because it's close enough that we can come back and re-terraform the place. And maybe these Unobtanium meteorites can somehow be turned into mecha metals (though it's an extremely energy intensive process, so it's not like just anyone can do it in their backyard).

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The only think that I could think would give an advantage to mechas would be a direct command interface to the mecha driver (so he does not steer the mecha through handlers and buttons, or even by a exosuit, but directly by thought).

This would give all vehicles so controlled a much improved reaction time. Mechas being somehow humanoids, it would become more natural to the driver to control most of its movements, so it would be faster, easier to learn to use it, and would let the driver do the moving automatically and concentrate in other aspects of the battle (tactical consideration, weapon systems), etc.

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You want it to be viable.

It must fulfill all of these criteria

  • It is economic to deploy
  • Effective against what it is meant to face (MBTs, Helicopters, Infantry, APC, SPGs and etc.)
  • Highly agile
  • Technologically viable
  • All terrain capability
  • Multi Role
  • Can be deployed to the battlefield very fast (Dedicated carrier rotorcraft, Transcontinental fixed wing carrier or Put them inside a ballistic missile warhead.)
  • Easy to use
  • Long operation period
  • Long operation range

The reason for the above is to make Mecha units viable, not effective!

If we are going to talk about effectiveness you'll have to go a bit more technical. That's why I put the reason "Technologically viable".

With all think-tanks out there, we may see a bipedal or multipedal mecha in the near future.

as long as it doesnt fly like a fighter it is viable in the near future if given thought

It will be the ultimate land superiority weapon. A nightmare in urban warfare

If you want a reference about how effective a mecha can be to a modern army with nearly technologically viable technology(Carbon tube EAP, Cold Fusion reactor, Advanced ballistics, Vetronics(Vehicle Electronics), Sophisticated sensors, AI, Redundant pneumatic hydraulic systems, muscle package, and etc.) Watch or read Full Metal Panic. It's nearly realistic with 10 meter tall bi pedal mechas. Just dont think Lambda Drive is viable though.

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    $\begingroup$ Bipedal is far harder to design a control system for, and less stable in any case, than quadripedal. Hexapedal may be easier than quadripedal. Engineering isn't far enough down that road to say at this time. Don't be fooled by evolution: all large land-based life is descended from fishes which fixed us with a four-limbs-plus-tail body plan a long time ago. Bipedal is necessary in order that humans have hands and can make/use tools. On some other Earth centauroids might be better-adapted, but there's no way for them to evolve from reptiles/birds/mammals. $\endgroup$ – nigel222 Dec 7 '15 at 10:47
  • $\begingroup$ Yes, thats the missing part of the puzzle... if we are to succeed with bi pedal designs, we need to understand how does movement affect the center of the gravity and make it that way that any bi pedaled robot is able to stand on its own to feet automatically $\endgroup$ – mico villena Dec 7 '15 at 12:03
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In my mecha-infested RPG, I had two historical prerequisites for mecha:

  1. Exterminate the horses during the medieval period, forcing the heavily armoured cavalrymen to walk,

and

  1. Remove gunpowder from the catalogue of the tools of war. I did this in my fantasy world by saying that in the particular magical environment they had, there are no fast non-gaseous oxidisers.

The combination of these two factors leads to the concept of powered armour earlier, and the lack of gunpowder limits the capabilities of projectile weapons, leading to the concept of hand-to-hand combat between the mecha.

Once projectile weapons become king of the battlefield, minimising target silhouettes becomes of paramount concern, and will favour tanks over mecha.

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  • $\begingroup$ Can your mecha stop/withstand/doge a ton? No gunpowder needed! $\endgroup$ – Wayne Werner May 21 '16 at 14:08
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Mecha, especially humanoid mecha would be incredibly useful in a supporting role, think combat-engineer. If you need a bridge get the mechs to do it, if you need debris cleared the mechs can do it, if you need defences built and trenches dug the mechs can do it. If you need supplies moved or large munitions loaded the mechs can do that too, basically your mechs give the army functional versatility, and they can still be deployed as fire support in particularly mountainous or densely-packed urban terrain.

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    $\begingroup$ Hello Cognisant, all these things you mention can be done by standard vehicles as well. There are even dedicated types of vehicles for the tasks you mention. Can you go a little more in depth on why a mecha would be more useful in this case? $\endgroup$ – T3 H40 May 19 '16 at 6:43
  • $\begingroup$ Rather than having an assortment of dedicated vehicles the one mecha could perform many roles. A bomb-loading cart is totally different to a forklift which is totally different to bulldozer which is totally different to a crane. Furthermore none of these vehicles could reliably climb a steep incline or cross a river on their own. $\endgroup$ – Cognisant May 19 '16 at 23:04
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One thing mechs have over traditional wheeled or tracked vehicles is impromptu modularity. Since they have hands they can pick stuff up. Need to dig? Grab a giant shovel. Need to build? They can pick up and lift materials. Need to fight? They have hands to work anything from rifles to missile launchers. While you can swap out the turret of an armored vehicle it isn't a fast or easy process.

So imagine an expeditionary force that needs maximum flexibility with minimal payload weight. Their mechs are environment suits, construction, repair, and security all in one. Sure, nothing is as effective as a main battle tank, but those things could be too heavy (even now our largest planes can only carry one tank) to even make the trip.

Plus if you set up the tech so that offensive weapons have far outstripped defensive tech (so that infantry can easily destroy MBTs) then there is more pressure to be mobile and flexible than armored, so a humanoid fighting vehicle may have benefits over traditional vehicles.

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    $\begingroup$ The added weight and complexity of fully humanoid articulated hands and limbs might 'look cool', but they are wasteful engineering. They are less capable than specialized components - why have giant cartoonish shovels instead of a vastly more efficient bucket loader attachment? The same principle applies to any other device - giant human-like ergonomics are silly, and swapping components for a vehicle will not be any different than for a mech. Minimal weight would be wheeled vehicles, not overly-complex mecha, not to mention the benefits of distributing the weight instead of small footprints. $\endgroup$ – pluckedkiwi May 20 '16 at 18:16
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    $\begingroup$ Sure, specialized always beats multi-purpose, unless space is at a premium. If a mech plus gun, shovel, and ax weighs less than tank, bulldozer, crane, and tow truck, the compromise may be worth it. The mech can just pick up new items, but swapping out turrets or prow attachments on vehicles can take time and require a motor pool. Anyway, it may be a convincing enough reason for the fiction. $\endgroup$ – Jason K May 20 '16 at 20:31
  • $\begingroup$ In order to function equally to a vehicle, the mech would need to be bigger and heavier to begin with (lots of moving parts and articulation and surface area to armor). Add to that the absurdly big shovels, guns, etc. all shaped to fit mecha-hands, etc. (none of which belong outside of a child's cartoon), all being necessarily bigger than just the specialized component, and size greatly favors the specialist. More mount-points on the vehicle gets multiple devices - hauling around a wagon full of novelty-sized tools for a mech is just silly (even additional mounts on the mech make more sense). $\endgroup$ – pluckedkiwi May 26 '16 at 15:43
  • $\begingroup$ I dunno pluckedkiwi, my hypothetical scenario is just as plausible as your hypothetical dismissal. Since no viable mechs exist it is hard to argue their weight/power ratio versus vehicles. What maintenance requirements do they have? How many operating hours before a major overhaul? What defensive and offensive technology is present? There are far too many unknowns to effectively debate this issue. I merely presented a situation where mechs, due to modularity (if they even have hands), MAY present an advantage over a traditional mechanized armor unit. $\endgroup$ – Jason K May 26 '16 at 19:21

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