willyolio pretty much nailed everything, but if I would add a couple more points they'd be:
-First, I'd say that generally making the vehicle a bad target would be enough of an advantage that it might gain some ground towards a production line. This is why helicopters are considered viable tank-killers; even with stuff like spread shots, it's still difficult to hit a chopper that moves so quickly and has the advantage of having no ground nearby to aim at in order to score a hit through shrapnel or the explosive radius.
With a bipedal mecha, you'd need to build and program something capable of mind-bending acrobatics and structural contortions to give it any chance of becoming harder to hit, while still keeping it armored enough that the splash damage from near-misses wouldn’t kill it. But assuming this is actually possible, the opponent could more cheaply make their own investments in tank gunnery, by ramping up auto-targeting systems, or increasing the volume of fire.
If it comes to some kind of arms race, the guys who have to balance a giant robot are going to lose to the guys who just have to make sure their gun is pointing in the right direction.
But even if we pretended you could build some kind of ridiculous Le Parkour mech, keep in mind that helicopters are viable because they can play plenty of other roles beyond being a tank-killer, to make up for their cost.
-Secondly, if there really are situations where legs have an advantage over treads, it's much more practical to stick them to the body of a conventional vehicle.
When you start getting into battles where movement similar to a human's becomes so exclusively advantageous, you usually have to work up something quite contrived...
For instance: A battle in an extremely dense urban center where the structures are tall and difficult to smash through, with no opportunity to level the city beforehand, where the infantry, air, and artillery support from either side make killing a highly armored target incredibly difficult, meaning insertion by said armored targets is the best tactical option; the buildings and alleyways are so tight that it is nearly impossible to rely on anything with a wide turning radius or gun barrel that lacks maneuverability, and while just using the tanks to level the city could be attempted, an attacking force that swiftly directs their armored weapons into choke points or to make pinpoint blitzes stands to defeat the other more decisively.
And still, once you've gotten here, there's next to no reason why any force would have these mechs on hand, since this is one of the few instances where they could have possibly had an overwhelming advantage by deploying them. Their tanks will mostly get the job done, and that's probably what they'll use, instead of adapting a major line of production for one circumstance that might not even be pivotal to the entire campaign.
I'd say that when you start pulling up these scenarios, however, it's time to back up and think about whether or not armored tanks are productively viable against other modern armies, with modern anti-tank weaponry being what it is.
I'd really have to agree with Matt, and go further to say that tanks are starting to share some of the same problems.
While modern day, top-of-the-line tanks can fairly consistently resist dated RP Gs, the anti-tank weapons that infantry, light vehicles, choppers etc in modern armies have access to are much more destructive and sophisticated. Overall, the trends indicate that the great majority of the time, quicker, cheaper, more versatile units will trump attempts to make a deployable weapon immune to fire.
In other words, of the weapons we have available, it's the first strike capability, coupled with just enough firepower to ensure that you only have to shoot once, that destroys opposing enemy forces most effectively. And logistically, infantry with good support seem to be so much more capable of this role than heavy armor does.
Situations do exist where pouring money into the development of armored divisions achieves victory, but given how few and contrived they are, they are usually not so pivotal that the war rests on their outcome. Otherwise, heavily armored vehicles cannot operate on their own, when they are pitted against well-supported infantry that can kill said armor from a respectable range, with accurate, nigh unavoidable weapons, which cost tiny fragments of what went into building the tank, training the crew, and maintaining it on the battlefield. Even in a support role, other vehicles are usually more adaptable than heavy tanks are, and work better in tandem with infantry, meaning they're limited even there.
I think one could write fiction where those contrived situations did come up often enough in some strange, alternate society's kind of warfare, so that having large fleets of modern armor would somehow be justifiable. But still, you'd have tanks long before you'd ever have combat mechs.
I guess if one were trying to avoid an outright fantastical handwave, there would need to be lots of development towards the political, cultural, and scientific developments leading to the outlandish decision-making that would result in a combat-oriented bipedal robot. As so many people have said, if it comes down to a sort of empirical consideration, the data suggests that the extremely paltry number of situations where it pays to have mechs around would not justify the costs you'd need to sink on building them in the first place. You'd need a form of warfare that somehow ended up drastically different from what we know of today, on top of a group of bumbling fools and timely coincidences that could somehow induce the production of battle mechs, in spite of other available options.
Of course, by then, there’s probably too much attention paid to the whole realistic side of things to easily transition into a Rule of Cool mech battle. Maybe this is the kind of setting to be reserved for a satire of the genre?
^ Except people are building them in reality. Mecha have actual basis in cold hard science.
Also to further talk on the tactical benefits of a mecha:
In some cases legs are preferable. For example mountainous often forested regions like Afghanistan, Korea and Vietnam are ill-suited to wheeled and tracked travel thus restricting mechanized units to areas with roads, leaving only either marching infantry or air mobile divisions capable of engaging the enemy anywhere. A bipedal mecha has all the transit advantages of a marching infantryman for the firepower of mechanized unit like an IFV. A Spider Tank in this terrain is about as useful as a real tank in that it's maneuverability is severely compromised.
The point is, it's easier to walk through the woods and mountains in a bipedal mech than any other design short of air transit.
Making a realistic mecha is going to leave it relatively small scale (as in probably no taller than 6 meters maximum) and not just because of the Square-Cube Law. Cost concerns dictate it would be better to have 200 mecha that are twice as tall as a man than have 2 that as tall as some buildings. (Even if the larger ones are more or less immune to infantry weapons of any kind)
Now obviously mecha are going to be playing very specialized roles. In large expansive areas like the Great Plains, the Golan Heights and the Tigris/Euphrates basin, nothing is going to beat a horde of tanks to take and hold ground. Sure helicopters could kill most of the tanks as could anti-tank infantry but helicopters can't hold terrain and infantry require support to hold it against other parts of a combined arms attack. What this means is mecha are probably going to be literal mechanized infantry as a shock trooper or special forces type unit. More firepower such as 20-40mm autocannon, various short range missiles and better protected than infantry but at the same time if the mech is small enough it has the advantages of an infantryman in forest, urban, mountainous and uneven terrain.
Basically of all types of mecha from Powered Armor to Super Sentai Humongous Mecha (or the Tengen Toppa Gurren Lagann), the Mini-Mecha and smaller forms of Humongous Mecha make more sense. Powered Armor isn't likely going to be something resembling Space Marine armor from WH 40 K, more like something out of Halo and other sci-fi that's basically body armor with augmenting abilities.
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I think that mecha can be in science fiction, despite being unscientific.
'Science fiction' does not mean that 'this work only uses principles justified by science'.
Unless, of course, your definition of fantasy is 'any work where the core mechanics are not justifiable under scientific principles', in which case it would have to be.
Mohs Scale Of Science Fiction Hardness, anyone? If a work has mecha, it's at LEAST at No FTL or higher. The hardest show I can think of in this genre is Flag.
I think the Mini-Mecha might see action in the civilian sector since I have no clue how it would surpass a for example highly trained special ops or mechanized unit in flexibility, agility and mobility, especially in complicated terrain.
The Humongous Mecha on the other hand is utter nonsense and belongs in the fantasy genre.
edited 11th May '11 1:24:30 PM by MattII
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It seems you misunderstood what I was trying to say.
My point wasn't that mecha are realistic, it was that they could be part of the science fiction genre, despite being far more fantastical than most elements of the genre. Not as fantastical as Faster-Than-Light Travel, but pretty far out.
also, people forget about the idea of flexible robots like the snakebot or a centipede-bot. They're just as maneuverable through tight forests while remaining much more stable with a lower center of gravity.
humanoid mecha suck.
forested regions are just as bad for big mecha anyways, because soil is soft. if you need armour in that area, bring a tank and just start mowing down the trees. Legs on big, heavy vehicles are only better in the most contrived circumstances:
- tight maneuvering space (as in, less space than a tank can turn, which can spin on the spot)
- extremely hard and solid ground (again, legs = higher pressure on the ground)
- stepped or jagged surfaces (treads are universally better on smooth-ish surfaces - the M 1 A 1 can climb 60% grades - and most people are unable to walk up a 50% smooth grade without slipping, losing balance, or going down to all fours.)
so... where are you going to find terrain with exceptionally strong ground that can handle the pressure of a mech's feet, so tight you can't fit a tank, and specifically is jagged enough that treads simply won't work and can't get enough grip?
If you need any point of reference for how "mobile" big things with legs are, just see where elephants like to go. Not the mountains, that's for sure. They'd be slipping and sliding to death all the time. any robot that wants to go where treads can't had better stay smaller than a billy goat or mountain lion (about 100kg max).
Oh, and just because some people are building it for fun has absolutely no bearing on whether or not it's practical. Here's a guy with a chainsaw bayonet, for reference.
https://www.youtube.com/watch?v=8-ScV2jFiUg
edited 11th May '11 3:50:38 PM by willyolio
I take it you've never been in dense coniferous forest before. There's an old Injun saying about the forests of California that "the trees support each other". This is amply true in the Sequoia Sempervirens redwood. The roots are shallow and wide and weak. A lone tree no matter how small or large is easily blown down by a light wind. Yet get a 100 acres of the things and all of them will survive hurricane force winds and not even flinch.
This effect is seen on just about every conifer in North America. Get huge tracts of coniferous forest and it survives very well against all challengers. In clustered forest like that, you cannot push a fullgrown tree over with a bulldozer at full power let alone think you can just plow through the things with a tank.
Meaning forested regions with that property are impassable to tanks and other mechanized forces.
Also, the issue about soft soil is really only existent in swampy regions. Temperate to semi-arid forests like that of Korea, Afghanistan and commonly found across the North and Western parts of North America have very firm soils almost made entirely of rock.
Now true this doesn't justify bipedal mecha alone, but it does provide fodder that small scale 3-5 meter tall mecha as plausible in certain environments. As I said, humanoid mecha are likely to be highly specialized roles with the most generalized use being literal mechanized infantry if the mech is on the smallest scales.
Remember when I say they have the advantages of an infantryman, I mean it. They can hide in places tanks can't go if they are small enough. A mech 3 meters tall, 1.5 meters wide and operated like the forklift from Aliens would fit into narrow alleyways, be able to hide behind buildings and dense forest (or other concealing landforms) and at the same time could carry far superior firepower than any infantryman.
Nobody's talking about making the things fight room to room. With literal mechanized infantry like that, if an infantry foe wants to hide in homes and buildings in dense Urban Warfare like that, they better be prepared to see the mechs opposing them to bring down the building on top of them with a well-placed ATGM or their cover punched through or shredded by autocannon fire. Humanoid mecha presumably would be armored enough to repel any kind of rifle fire and possibly 12-7-14.5mm heavy machine gun/anti-materiel rounds. Thus they suffer the same real drawbacks as anything else in urban terrain, chiefly the guy with the man-portable recoilless rifle/rocket launcher like the Carl Gustav M3 or the RPG-7. (Weapons which are incredibly lethal and dangerous to even the mightiest tanks.)
edited 12th May '11 6:43:04 AM by MajorTom
I'd have to more agree with Tom here. Rough terrain and urban combat are a great niche for mecha style units. Tanks are notoriously bad in those areas and helicopters can't hold ground. So I think as infantry, it'd be nice to have a little heavy weaponry, in the form of mecha, to go along with you.
If you use the mass reduction particles in the OP, then the mecha can start to carry tank-equivalent weapons and be extremely useful.
edited 12th May '11 1:41:39 PM by MattII

I've got no problem with Rule of Cool uses, just as long as no-one posits them as combat-practical in any way
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