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Saw Pacific Rim for the first time with a friend recently; I'd never really thought too hard about giant robots/been as into Mecha and Gundam stuff as some of my friends before, but the Jaeger concept got me kind of in the mindset for thinking up Fun Robot Designs, and now I'm trying to come up with some fun designs and quirks that make sense for something like fighting Giant Kaiju-Style Monsters, but which I haven't really seen in other designs I've looked up?

An idea that I thought would be super neat is to basically have a Smaller and more compactly-built Jaeger-Type Mech, built to use its low center of gravity to its advantage and get up-and-under bigger foes to attack them where they're more vulnerable, use their opponent's own weight and momentum against them, and sacrifice increased size and outright lifting capacity for greater Durability (I noticed there were a lot of problems in the movie with Bigger Mechs not having much in the way of Crumple Zones, and being Long and Tall seems to come at the price of Balance and Stability- I like the idea of a Little Mech that's built in such a way that even if you do manage to crush it, the ways in which it Crumples/distributes stress shields the people on the inside and gives them time to either Recover and Fight On, or Bail Out if necessary). I also liked the idea of this bot having a sort of "Spring-Loaded" feel to it, something that can absorb a lot of physical shock and Bounce Right Back- Maybe even using the shock of your own attack to bounce back at you. XD

That made me remember things like prosthetic running "blades" and jumping stilts, and thought it would give the mech that spring-loaded feeling, improve its mobility when fighting large opponents across things like cityscapes and different terrain, and look really cool and unique if I could somehow incorporate something like these into the design of my Mech's legs!

This isn't really something I've seen in very many Mech Designs, but that begs the question: Is that because someone who is Better At Robots than Me has already figured out that there are more disadvantages to this than advantages? I remember the argument about whether or not these sorts of prosthetic limbs gave human athletes too much of a competitive edge to allow them to compete alongside runners with Regular Human Legs, but is there any reason why this would be a serious design flaw for a mech, or impair the mech in some way? I'm sure there are disadvantages, everything has those, but do the disadvantages of a "blade-stilted" mech outweigh the potential advantages of one?

I guess what I'm trying to get at is this: What advantages does a mech with "traditional" legs and feet have over one with Running Blades, and Vice-Versa?

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    $\begingroup$ May I ask, why build a mecha like this? for war? Weapons of the mech? Basically what do you want to achieve if you built this mecha, then we can tell you if its viable or not. $\endgroup$ – Mr.J Jan 10 at 0:22
  • $\begingroup$ Ooops. You'd better change your question's title to reflect the in-body answer. It caused confusion. @Mr.J's right, when the pure concept of 'viability' is considered, no mecha is 'viable.' But that's not what you're asking. $\endgroup$ – JBH Jan 10 at 1:11
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    $\begingroup$ Plausible Reasons for usage of Combat Mecha $\endgroup$ – Mazura Jan 10 at 1:28
  • $\begingroup$ "they will be dependant on a surface that can be walked on, even if it may be able to be more jagged or steep than a surface a tank could traverse. It would have to have very big feet for balance and to support the vertical weight." – BornToDoStuff $\endgroup$ – Mazura Jan 10 at 1:31
  • $\begingroup$ I don't have enough for a full answer; but it part it could be built that way to take advantage of mechanical advantage; the whole "give me a lever long enough..." quote $\endgroup$ – Marky Jan 10 at 15:20
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I have asked a lot of questions about mechs in this site, every viability of them, and I even made spider mechs. I even created the "mechs" tag . All of them have one thing in common.

NONE of them are viable

First to note is the cost to create one. I doubt one would be cheap since engineers will have to think of ways of how to counter a barrage of solid sabbot from a tank so your mech can somehow withstand or dodge the attack, and that will cost a lot.

Second is... the weakness a mech posses, specially humanoid versions. Destroy the leg.

Third is range weaponry, tanks are the beasts in the battlefield because they could fire accurately AND pack LOAD of punch! Their center of gravity is so low that firing their cannons will hit the target almost 100% of the time (provided the target is not moving) and still withstand the following recoil the cannon gives.

Do take note that's just countering a tank, we have yet to consider the munitions of every.single.weapon that we currently have(fighter planes, rockets, etc etc), how can a Mech withstand these threats? Are they realistic? How much might that be?

Mechs wins in the rule-of-cool match against tanks but viability wise, its the opposite.

I think your mech idea might be more viable as a powersuit, like Iron man. But I think that's for another question.

EDIT: It may seem I have to give my shot on giving my answer to the "viability" of bladed Legs OR Cheetah legs, I'll be giving my answer for both, WITHOUT the knowledge or purpose of these legs.

  1. Bladed Legs Or Stilted Legs: On humans they pretty much increase the height or your jump, the distance of each stride, granting you more mobility than a normal human AND can maybe used as a weapon (though this seems a bit dangerous as it compromises the integrity of your legs) This might be addressed by creating the legs similar to this. These legs are just made from 3 main parts, the thigh, knee and leg (from knee to foot). The thigh and knee are connected by well oiled bearing enclosed and protected by the knee (sorry I can't give you a precise illustration about this mechanism).

With these legs, this wont be used at urban areas for rescue and civilian duties because the legs will always drill down concrete. It is best used though, on urban warfare and rocky areas. Desert (specially sand only ones) forest and swamps are its worst workplace as these legs might be more of a hindrance than a advantage because they might drill very deep in these areas, restricting the granted mobility of these legs.

My Personal Analysis:

These legs might be more successful if equipped to human cyborgs or as a powersuit. The users can be equipped with sub machineguns and grenades. Give the user light armor than can protect it from most rifle rounds. the cyborg or powersuit is not invulnerable though, so it may fall down after several shots by high powered rifle, explosives and machine gun fire but its added mobility might help it bring down a couple of human infantry men, and a well placed kick might incapacitate a tank, before being destroyed.

These legs however has several drawbacks:

  • Stealth: I can't seem to find a way to make these stilted legs to be stealthy, as they seem to drill holes on the ground each time the user steps, so the preferred usage of these units overall are ambush or full frontal assault. They might be best to be used as "take no prisoners" units, they are too, good in torturing humans for intel.

  • Turning: With the absence of feet, a quick turn is noticeable which might be a problem because veteran snipers might pick you with a single shot. I have not yet found any advantages of turning using your waist, so I'm going to assume that its better if the user will use the high mobility legs to dash forward, then jump turn to re engage enemies.

  • Costs: This might be debatable since a well placed jump kick dive can destroy a tank, then proceed to kill the infantry with its guns and explosives, however, the cost to built a cyborg to use these legs are neither cheap nor humane. Human transfer is the cheapest and best option because the brain can store at almost infinite information, and with the help of a computer, complex attacks might be possible. I do think that human flesh too will make the cyborg lighter, putting ceramic armor vests for protecting might increase the mobility of the cyborg because its armor is lightweight. So long as the cyborgs destroy an average of 2 tanks and maybe 24 infantry, I can say that this might be a viable approach

NOTE: Do take note I created a cyborg because I think large mechs will have loads of problem using this. Examples are recoil and weapon choice.

  1. Cheetah legs: IMO are the worst legs that you can put on a mechanized unit. Cheetah legs are slim to help cheetahs run at full speed. Slim legs for a mech however, reduces its grip for handling recoil. WE might create a mech, a lifesize cheetah mech that is capable of slashing its way around the battlefield with a retractable sword on its sides then maybe 2 rounds of armor piercing missles that can penetrate a tank's armor. BUT as long as we don't have a lightweight blade capable of cutting a human leg bone like butter then this legs are useless. Maybe for scouting purposes but, we already have aerial drones for that.

TLDR: Creating a mechanized unit with these legs, especially the stilted one, might sneak to be a viable idea IF certain conditions are met. They are still faced with the common problems a regular infantry men faces(mines, IEDs,etc...) , or even a tank. But these doesn't change the fact that their greatest weakness is handling recoil. Giving stilted cyborgs small firearms and explosives is the most plausible thing to make them viable for war.

They are restricted also for War use only, rendering them useless during peacetime. You can ride a tank on urban areas but you can't use the stilted legs, well maybe the cheetah can be a fast ride, so is a F1 race car.

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    $\begingroup$ tanks are the beasts in the battlefield because they have treads and a ridiculously low CoG. Destroying the leg might be kinda hard if it's almost entirely sunk into the ground, but then why bother. Just don't be where it lands when it falls over. $\endgroup$ – Mazura Jan 10 at 1:25
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    $\begingroup$ tank vs mech is like comparing jets vs helicopters. You don't deploy choppers because they are faster, more efficient, or more economical than a jet. You deploy them because they can do missions a tank can not. Jaeger sized mechs are useless, but tank sized mechs could fight in harsh terrains that tanks can not go. Imagine weaponizing this new Hyundia vehicle bbc.com/news/technology-46794087 and you'll quickly realize that in the right warzone, they won't just be a better option, they will be the only option. $\endgroup$ – Nosajimiki Jan 10 at 4:18
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    $\begingroup$ @Nosajimiki raises an excellent point: The Japanese SDF have spent 50 years fruitlessly defending Tokyo with tanks, missiles and many types of ground-based and airborne super-weapons. But only Mecha-Godzilla (and a select few monsters) have successfully fought Godzilla to a draw. $\endgroup$ – user535733 Jan 10 at 4:29
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    $\begingroup$ Note that the question asks "What advantages does a mech with "traditional" legs and feet have over one with Running Blades, and Vice-Versa?" - that mechs in general are cool but not viable is sadly correct but irrelevant. This question is about the viability of jumping stilts legs vs. "standard" mech legs. $\endgroup$ – G0BLiN Jan 10 at 12:17
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    $\begingroup$ @G0BLiN edited my answer to what I think will make these legs viable. $\endgroup$ – Mr.J Jan 14 at 5:39
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Stability is going to be a huge issue. If you take a foot and ankle, it provides with you a large amount of control and a lot of different ways to apply force into the ground to keep yourself standing (think of standing on a rocky bus/train trip). With a spring type, you lose all this flexibility and you will need to compensate for it by moving your upper body and readjusting your stance.

You will also need to synchronize your movements with the spring which limits the range of movements you can perform and the ease and conditions you can perform them under. For example, Muddy or soft ground will slow you down as you sink in. If you foot is stuck if will stretch and pull you back before you can free yourself, when jumping you need to time it with the down and up motion of the spring to maximize your jump, when kicking something the spring will compress reducing the effect. You might also have problems standing still, especially on sloped ground and the effects of debris and obstacles are going you to readjust your stance since you have no ankles and your point of contact with the ground isn't flexible like feet are.

Also I'm not sure if we could actually make a spring that could support a mech as large as the ones in pacific rim. Springs deform and return to their original shape, but once a spring is large enough, its going to deform at different rates depending if the material is on the outside or inside of the spring and this could permanently damage it.

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This is a very clear case of engineering that does not work at scale. As you scale up metal springs, they become less like springs and more like memory foam. By the time you get to Kaiju scale, they would not offer any meaningful advantages unless designed from materials that do not yet exist. Such a design would likely require a more pneumatic hammer like system to even approach feasibility.

That said, your idea of a stout top armored mech made me picture a Puma from Mechwarrior. enter image description here

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  • $\begingroup$ those legs look pretty tall, how about a rocket launcher? $\endgroup$ – Mr.J Jan 10 at 8:30
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Springs As @nosijimiki has answered, springs don’t scale well, due to physics.

Also remember that as the height of something doubles, the volume (and so mass) cubes. This means the burden on springs goes up incredibly fast. Furthermore, the density of a mech would be far higher than a human body.

Whilst a simple leaf spring works fine for a human runner, a monster truck needs big oil/coil springs to give it (proportionally far less) bounce.

I can’t think of anything larger than that which has ‘bouncy’ springs; it tends to be shock-absorbing.

crumple zones You also asked about crumple zones. Crumple zones are used to protect from the sudden deceleration caused by a (blunt) impact against a wall, another vehicle, etc.

They sacrifice the vehicle to protect the occupant against lethal or life-changing injuries.

However, most weapons (bullets, shrapnel, etc) are penetrative rather than blunt impact. Crumple zones will not help protect against these. Rather you need rigid armour to prevent penetration - you may want some impact dissipation below this, but generally the rigid armour will spread the impact thus dissipating it. Ablative armours also work here.

Weapons also function by shockwaves from explosions; The standard method to protect against this is a layer of (rigid) armour, then padding, then another layer of armour. But again, crumple zones offer no protection.

So you don’t see crumple zones on tanks, because they’re useless. You probably do get them on military jeeps, but that’s to protect the occupants in an RTA, not against the effects of war.

The only thing a crumple zone would protect a mech against is a blunt impact like a punch/kick from another mech. Realistically, fighting mechs like this is not viable. But suspending disbelief for a minute, remember that crumple zones sacrifice the vehicle - so if you’re relying on crumple zones, you’re accepting that you’re sacrificing the mech when the first punch lands. That’s probably bad economics for a war, and certainly won’t produce cool fight scenes.

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    $\begingroup$ For the shockwave thing, you don't want a solid/rigid armour - otherwise you get spalling from the inside surface of your cockpit, turning "shockwave" into "shotgun". A thick layer of armour, then a layer of padding, and then a second, thinner, layer of armour will work though $\endgroup$ – Chronocidal Jan 10 at 15:21
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    $\begingroup$ @Chronocidal thanks, that makes sense. The outer layer would be rigid though? $\endgroup$ – Dan W Jan 10 at 15:23
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    $\begingroup$ What is an RTA? $\endgroup$ – a CVn Jan 10 at 15:34
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    $\begingroup$ @aCVn sorry - Road Traffic Accident - it’s a common acronym in the U.K. $\endgroup$ – Dan W Jan 10 at 15:56
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    $\begingroup$ @DanW Yep, both inner and outer layers can be rigid, so long as the padding is not, . It's similar to cavity wall insulation, or a fire-break in a forest - a gap that the shockwave cannot travel through. $\endgroup$ – Chronocidal Jan 10 at 16:22
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To address the problem with a "blade-stilted" mech you run into issues with surface pressure very quickly.
pressure equation
You can see from this equation that pressure is force divided by the area it is exerted over. We can extend the equation for force as such:
force equation
With the sheer mass of a mech when you decrease the surface area supporting them you increase the pressure they exert per square foot and the earth can only support so much pressure before your mech just starts to sink in and lose efficiency and mobility.

Decreasing the surface area of its legs to blade points would likely have the effect of its blade sinking most of the way into the ground making it impossible to be agile, any attempt at sudden movement causes a dramatic increase in pressure which would first cause your mech to sink further until frictional forces against the sides of the legs can support the added pressure. Whether your mech would have the range of motion or power to then withdraw its sunken legs from the ground is then questionable.

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