I've been a fan of Battletech/Mechwarrior IP for almost 20 years, but I have to admit, the apparent absurdity of the 'walking tank' idea (to many) has always put a bit of a damper on things. I'm currently working on a quasi-hard space opera world building project, and I've been debating on whether or not I should include walking AFVs into the "universe" that I've been putting together. I'm trying to keep handwavium and absurdities to a minimum. Consequently, as much as I like the idea of mechs, I have to consider leaving them out if they are too much in the realm of fantasy. Surprisingly, when I consider recent breakthroughs in nanotechnology such as nanotubes, graphene muscles* and weaponized lasers, I find it harder and harder to dismiss them outright.
One of the biggest problem almost always cited for real world mechs is ground pressure. This can be a major problem for tracked and wheeled vehicles. Too much ground pressure and a tank will have difficulty moving over soft terrain. However, I think it's a mistake to assume that this applies equally to a walking machine. The largest land animals that have ever lived, the sauropods, weighed up to 100 tons, and we know for a fact that they at least occasionally moved over soft, muddy ground because we have preserved footprints. I am not aware of any tracks that indicate that these animals were sinking knee deep in mud. Read up on elephant feet if you want to understand how these massive animals were able to walk through mud.
The largest *bipedal* predator to ever walk the earth (Spinosaurus) was semi aquatic and was as large as some whales. This is an animal that may have weighed as much as 20 tons, walked on two legs and lived in wetlands. The reason walking through mud wasn't a problem for this animal was due largely to its foot design: the toes spread out on the ground, but when the foot was lifted, the toes pulled together, allowing the foot to easily slip out of the mud. Humans aren't very good at doing the same because our plantigrade feet practically act as hooks once they sink into the mud. A mech would need either broad feet, toes that can fold up like a bird's, or elephant like foot pads that can reduce their size as they are drawn from the muck.
With these two real world examples, animals which weighed as much as armored vehicles such as a tanks, I think it's reasonable to assume that a walking vehicle, if designed properly, might be more effective for moving over soft terrain than a wheeled or tracked vehicle.
Many fans are often stumped as to why there would be any advantage to bipedal locomotion. Upright legs are more efficient than spread, or splayed legs; this is why most archosaurs and mammals have upright leg posture. Bipedal locomotion is more efficient for walking than quadrupedal locomotion due to the pendulum like action of the legs combined with the fact that bipedal animals take advantage of what is basically series of controlled falls. Bipedalism in mechs would also mean less surface area to cover with armor and consequently less energy required to support its weight. Bipedal locomotion also seems to allow for greater running speeds for animals that lack a flexible spine. Since multi ton machines with cheetah like spines are unlikely, it's reasonable to assume that bipedal mechs might be faster than their quadrupedal counterparts.
Complexity and Vulnerability of the Legs:
This is another very common criticism of the mech concept. It is often assumed that these hypothetical machines would require an enormous amount of delicate machinery to power their legs, and an enormous amount of armor to protect it. The reality is that working graphene/polymer based muscles have already been developed. Graphene is so far the strongest material known to man: it's 200 times stronger than steel; you could place an elephant on a pen and place that pen on a graphene sheet as thick as shrink wrap and it wouldn't break. The amazing thing about this stuff is that it's conductive and it contracts like muscle. In the distant future, it's not a stretch to imagine super strong materials being used as muscles for robots that also double as a sort of armor. The legs of future war robots might actually turn out to be far more durable than tank tracks.
What about repair? I would imagine that by the year 3,000, machines will probably repair minor damage themselves via tiny robots. Machines might heal over time much like a living thing. That aside, repair might consist of swapping out damaged muscle fibers with fresh ones as explained in Battletech books.
With rapid advances in technologies such as a "braingate" and other forms of "cybernetics", we can expect people in the distant future to be able to control machines directly with their minds. It's not difficult to imagine that advances in this area may lead to armored vehicles that can be controlled as if they are an extension of the pilot's own body. Mechwarrior and other mecha series have touched on this with devices such as the "neurohelmet". With this in mind, one can imagine powered armor that is as agile as the human inside it.
This would be a real problem that could rule out erect walking vehicles leaving smaller "power armor", "mini-mecha" and/or more spider like designs being the only feasible concept. Being tall makes you an easier target. However, on the other hand it also allows for increased line of site. Directed energy weapons could become one of the dominant weapons on a far future battlefield due to their extreme speed and accuracy. They would be devastating anti-aircraft weapons, as well as excellent point defense systems capable of shooting down missiles and artillery rounds mid-flight. The problem is they can be severely hampered by dust, smoke and water vapor, they are also strictly direct LOS weapons, meaning you must be able to directly see a target to hit it. Because of this, the higher up they are the better. By being higher up off the ground, beam weapons would be able to fire over much of the smoke and dust that blows around at ground level, giving them a greater effective range. Generally speaking, the closer to the ground a directed energy weapon is, the less effective it becomes. Would this be enough to drive the development of higher profile fighting machines? I'm not sure, because it might be simpler and safer to limit the arsenal of AFVs to kinetic weapons and missiles.
This is my best effort to "defend" the mech concept. If my arguments contain serious flaws I want to know. If mechs really are as absurd as many claim, then I will leave them out of my world building project.
Of course I am aware that this is a Mechwarrior forum filled with people that have a 'pro-mech' bias. I've been having difficulty finding a high traffic tank forum, but I do plan on posting something like this there as well.
Edited by Sim Koning, 09 May 2012 - 02:42 AM.