Probing The Inaccuracies: Mecha

There’s something about a gigantic bipedal robot that inspires the imagination. Whether it’s the return to personal, one-on-one combat that many mecha-related series seem to explore, or the idea of a huge humanoid machine kicking ass, it’s pretty easy to see the appeal of mecha. It’s also difficult to dispute that they are, in fact, rather awesome.

Unfortunately, they are also completely pointless.

The first question that needs to be asked is, “What exactly is a mecha good for?” Putting aside clearly improbable designs that can freely fly, as found in the Super Robot genre, it would seem that the mecha would be designed as an analogue to the tank – or alternately, to displace the tank completely. This, to me, seems rather improbable, as the limitations of any of the common designs of mecha – bipedal, tripodal, quadrupedal or spider-shape – far outweigh any advantages conferred upon the machine by that design.

To investigate why this is so, we must examine the general form of the mecha in order to determine its typical characteristics.

The Vincent from Code Geass, a series which I feel gets things very, very wrong.

The first, and probably foremost, problem with this design, which appears to be representative of most mecha designs, is its high centre of gravity combined with only two points of contact with the ground. As anybody who has been pushed over before they have a chance to brace themselves will know, this leads to a considerable amount of instability. As mecha would require an improbable amount of flexibility and speed of movement in order to brace themselves after an impact, this would lead to the design being very easy to topple over, and thus incapable of taking any sort of impact without being rendered immobile and therefore useless.

Of course, an actual mecha design would be fitted with gyroscopes in order to prevent it from falling over when it so much as moved on any sort of surface that wasn’t completely flat, but there’s only so far that one can go with gyroscopic stabilisation, and of course, gyroscopes add weight to the machine. It really outlines the disadvantages of bipedal movement in anything that isn’t biological, humans only being capable of doing it efficiently due to their locking kneecaps and the ability to unconsciously maintain their balance with tiny, almost imperceptible movements.

It isn’t just bipedal mecha which suffer from stability problems and a high centre of gravity. Designs with more than two legs may have a more stable base, which largely negates the need for heavy and cumbersome gyroscopes, but they can be just as easily knocked over with a large enough impact. Once a leg is restrained or destroyed, instant stability problems occur, with the machine being rendered instantly immobile, and most likely falling over because of their inability to redistribute their weight unlike a biological organism. The vulnerability of the legs of these machines means that they are rendered vulnerable to tanks, close-air-support aircraft and even men with portable missile launchers. As it is difficult to distribute armour to the legs of mecha without making their movement cumbersome, it would appear that mecha would be limited immediately by the weakness of their legs.

The AT-AT from Star Wars, a series which may not have been realistic, but which outlined the ease of knocking a big mech over.

This isn’t the only weakness of a design based on legs. Leg movement is a form of reciprocating movement, where a piece of machinery repeats a back-and-forth (or up-and-down) movement. While this has proven to be the only successful form of ground movement in animals, reciprocating motion is not considered to be desirable for machinery which is used for propulsion. In engine design, a reciprocating engine requires far more components and usually wears out more quickly than an engine utilising circular motion, and attempts at replacing the piston engine in cars, planes and ships have been common ever since the development of the electric engine and gas turbine.

The gas turbine has displaced the reciprocating engine in all but the smallest aeroplanes since the 1960s, either in the form of the turboprop or the jet engine, while larger ships commonly use turbine engines in order to propel them instead of more complicated, more difficult-to-maintain piston engines. Only in cars and motorcycles has the piston engine persisted; the superior fuel consumption of such engines at that size compared to gas turbines and Wankel engines has allowed them to carve out that niche. However, electric engines utilise circular motion, and with the development of improving battery technology and hydrogen fuel cells, the piston engine will likely be displaced in this market as well.

This has relevance to mecha, because even piston engines convert their reciprocating motion to circular motion at the crank. If one were to directly connect the mech’s legs to the engine, one would either be converting circular motion to reciprocating motion, if a gas turbine or some sort of electric engine were used, or reciprocating motion to circular motion back to reciprocating motion if a piston engine were used. I hope you can see why that would cause apoplexy in many engineers; you’d essentially be transmitting power through another set of complex components, which adds more places for an already complicated machine to fail. If that doesn’t drive the engineers crazy, then it would definitely drive the mechanics that would have to work on it to drink.

It’s unlikely that a direct mechanical linkage to the engine would be used, for not only the reasons outlined above, but also because it would limit the flexibility of the limbs and leave them essentially as simple, crude metal struts. A far more likely system to be used is a hydraulic system, similar to the digging implements found on bulldozers. This would allow for movement of the legs more closely related to the movement of human legs, but would still be considerably less efficient than the movement of actual human legs. As discussed above, the locking kneecaps and ability to quickly change one’s balance lead to efficient bipedal movement in humans, but what would distinguish us from mecha capable of doing the same thing is that human muscles work on the microscopic scale, with nanoscale particles involved in the molecular biochemical activation of muscles. Ultimately, this scale allows humans and other animals to have impressive strength for their size, using a lot less energy than a comparative hydraulic system would use.

The Cauldron Born from the BattleTech series, a series which at least does things a little better than most mecha series. A little.

Returning to the general form of the mecha, apart from the disadvantages conferred by the instability of such a top-heavy design, the height of such machines leads to another obvious disadvantage: It leads to them being very noticeable. For something that purports to be an analogue to the tank, that is rather a significant weakness. Some people seem to forget that tanks are hardly invulnerable themselves; their tracks are potential targets to even outdated anti-tank launchers, while tank-on-tank combat can lead to the destruction of one of the tanks with just one lucky shot. As such, tanks attempt to decrease their profile and the amount of area to target by running hull-down, using terrain to disguise and cover themselves. This is not a luxury afforded to mecha.

The weaknesses of mecha versus tanks continues with mobility. By virtue of independent driving of both tracks, a tank can turn on its axis, while this is difficult, if not impossible for mecha to do. In order to turn the legs of a mech, one requires a complex series of components which far outstrip the complexity of comparative tank steering systems. As with the difficulties posed with reciprocating motion, these complex systems are useless for anything except making engineers and mechanics very angry.

Even then, the movement will be awkward, which would be especially dangerous in urban combat. Tanks are hardly the most appropriate weapon system in that sort of warfare either, to be fair; they are particularly vulnerable to improvised explosive devices and anti-tank launchers fired by people concealed in buildings, but mecha are even worse in these environments, with problems pursuing or retreating, which is rather problematic.

Just when you thought that there couldn’t be any more mechanical problems with mecha, physics comes and bites the idea in the arse again. Mecha are typically very large machines, and with increasing size comes an interesting correlation. For every squaring of surface area of an object, its mass goes up by the cube of the original object’s mass. While a human male may be on average 70kg, when that same humanoid shape is scaled up to several times that of a human, the mass increases correspondingly, such that mecha end up extremely heavy. A small increase in the height of a mech can necessitate the use of far more powerful servo systems and hydraulics, which is expensive not only in energy but also in cost.

The excessive weight of these machines can cause problems in other ways as well. A heavy machine resting on supports with limited surface area in contact with the ground leads to high pressure underneath. Tanks require wide tracks in order to prevent themselves from sinking into soft ground, but unless a mech had ridiculously wide feet, it would be likely to get stuck very easily in anything softer than concrete or baked soil, and to break up roads in urban terrain. Not particularly useful when you already have mobility problems.

Having discussed the weaknesses of mecha design, let me reiterate that I can still accept the inclusion of such machines in certain series, subject to some rules. I think the most important rule is that the series doesn’t take itself too seriously about the realistic use of mecha, unless there is a very good reason for their inclusion.

The second rule is that mecha in a series really have to “belong” – a criticism that I level quite heavily at Code Geass, as I don’t believe that an empire fundamentally deriving from the British would focus their efforts on huge mecha, as there is little in British tradition to suggest a significant interest in such developments. Ultimately, I think that the alternate history angle of this show, which actually could lead to a very interesting setting, is somewhat let down by the inclusion of something that doesn’t really fit. It might be said that I would need to watch the show with a certain amount of suspension of disbelief, but as the other instalments in this series of articles may suggest, that’s something I can’t always do.

On the other hand, BattleTech can be taken as an example of a mech-related series that I do enjoy. The mecha seem to fit better into the series than some other series involving such machines, and although there is a significant disparity between their portrayal of mecha and designs which would work in real life (insofar as such designs could work), they at least don’t portray the machines as invulnerable, giving it the heat-venting problems which add a bit of extra tactics to the series. I think it’s a good example of how to do mecha correctly without necessarily making them realistic.

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6 Responses

  1. Well the mecha series you have listed are the least accurate but mecha can be used more so in construction rather than warfare, and the best possible use of mecha in warfare is to carry a few shells and launch them and to put fear into their opponents and if designed large enough just squash the enemy (Big-O is an perfect example of this) also if you could produce a small enough nuclear reactor than most energy problems are solved when it comes to fueling plus if you use a series of treads at the feet you have solved many issues with locomotion, mecha would be absolutely useless for flight and anyone who says otherwise has watched too much Gundam . . . plus we have built several mecha such as the one designed by Neogentronyx . . .

  2. Forgot notification . . .

  3. @Raza: You make a good point when you suggest that mecha might be better served for utilitarian tasks rather than strictly military ones, as the form factor, if produced at perhaps the three- to five-metre range of heights, could provide a bit more lifting force if enough power can be imparted into the limbs to make up for that pesky square-cube law.

    The easiest way to do this, as you suggest, is to have some sort of power-plant which produces a lot of energy in a small space. While this might give mecha the edge they need for construction work and heavy lifting, in warfare, having that much free energy at your disposal would pretty much make UAVs even more threatening than they are now. A Cold War project, known as Project Pluto, was designed with the aim of producing nuclear-powered ramjet engines, and would have been able to stay airborne for an absurdly long amount of time.

    Of course, it did have some major factors against it, including the Mach 3 speed near the ground and the unshielded reactor which spewed out radioactive material. Perhaps the nuclear experiments involving the B-36 and nuclear engines are a more adequate example of how a nuclear engine could produce UAVs with terrifying range.

  4. This article is great. I read every BattleTech novel out there as a kid, and built Lego models of the illustrations in the books. Most of them were too tall or unbalanced to stand, but I once managed to build a Cauldron Born with hinge joints at the hips and a swiveling torso that could also freely stand. Along with gyros, the BattleTech series also made much to do about using the pilots own sense of balance to stay upright via neural connections in helmets.

    One thought: When you talk about utility for urban combat, tanks, APCs, Hummers, etc are not ideal for dealing with guerilla tactics.You mentioned roadside bombs, but what about traffic and other barricades? Wouldn’t a bipedal mech be better suited to escape urban traps?

    Also, they could possibly be used to retrieve men trapped on/in buildings in areas where helicopters cant reach them. Instead of parking a convoy at ground level, add some handholds and external harnesses to a mech’s arms and have them meet at the fourth of fifth floor. (A little more far fetched, I’ll admit)

    • @jpaul927: I think that a lot of the problems associated with armoured fighting vehicles in urban combat would still be associated with mecha; infantry still seem like the most useful force in confined spaces. Depending on the height that a mech could lift its legs, it might be able to clear simple barriers, but I doubt that there would be sufficient stability in a bipedal design to clear something like a Czech hedgehog [http://en.wikipedia.org/wiki/Czech_hedgehog].

      As well as that, anything substantially bigger than realistically-sized power armour (as in, not Space Marines in Warhammer 40,000) would still be unable to enter buildings and would have problems down tight alley ways whereas infantry could make flanking attacks from these positions. It might be worth researching whether powered exoskeletons could be developed to make urban combat for infantry more survivable; as for mecha, I still doubt their utility in this sort of purpose, as anything big, armoured and cumbersome is going to be disadvantaged in this sort of terrain.

  5. […] I have mentioned before the inaccuracy and unrealistic aspects of mecha as they are depicted in all but the most fastidious series and about how they are regularly depicted as being substantially more powerful than physics would dictate in a universe displaying a resemblance to the real world. That doesn’t stop me from enjoying a few series which bring mecha to the fore, the most prominent among these being the BattleTech universe. I first encountered the BattleTech universe with the animated series in the 1990s, which was admittedly poor-quality and inaccurate but was sufficiently exciting when I was eight for me to enjoy it. […]

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