What combat role could a mech play on a real battlefield?

[OutOnTheOP]

Any idea why the don't netfire Afghanistan or at least hot points and just send in a few squads and point out the Talitubbies? Seems it's just practical in theory or waaayyy too expensive, so risking a few more grunts is cheaper. F...king Politicians!

As for the obstacles, a 40* steep, wooded hillside trees lying around and you would go in there with an M1??? I learned something ABSOLUTELY different on the Leopard 2... but maybe the M1 is centuries ahead in secret technology, that enables it to do it. Our Tank drivers have been told never to try and pull of such stunts! ...same with anti tank ditches, need a bridge layer (or carry your own) to cross that... maybe if you go at about shallow angle and are extremely lucky you won't get stuck, but you're a very slow target.

 

They haven't NETFIRE'd Afghanistan because the program was deemed too expensive, and put on hiatus. Realities of funding a large military involved in two wars for a decade. Also, because the organic mortars are judged to do "good enough" for the current fight. Still, they continue to develop GPS-guided (and multimode) mortar and artillery projos, which fill much the same role. I would note that mecha, also, would suffer from the "too expensive for the return you get on investment" problem. Marginal improvements for a huge investment.

 

You're right, it's foolish to push tanks into difficult terrain, because infantry are at an advantage there. I would contend that a mecha in heavy woods of that sort is at much the same disadvantage as a tank, though: it cannot push over trees any more effectively than a tank (assuming it's of a similar weight class), so it still has to slowly pick it's way through them. It also has a lot more gangly bits hanging off it that can potentially get snagged by the trees and damaged. It can't see or shoot through the trees any better, and infantrymen in the woods can ambush it at close range with shoulder-fired AT munitions just as easily (or more, if you consider the large target profile).

 

Does a mecha offer some additional mobility advantages in certain terrains, sure. Is it more than a small incremental improvement? Not really. Can it's "agility" allow it to dodge incoming fire, absolutely not. "Crouching" doesn't provide an advantage, it merely reduces it's profile to closer to (but still larger than) a comparable conventional vehicle. And the accellerations that would be required are practically impossible, and would probably be lethal for the pilot, assuming it carried one. Does a mecha provide tactical advantages that outweigh it's disadvantages? From where I stand, most certainly not.

 

I'm not even convinced that the types of terrain a mecha has (arguable) mobility advantages in really MATTER: armies fight over terrain because the terrain offers an operational or strategic advantage, not just because it's THERE. High ground is advantageous... but only if it offers the opportunity to use it for observations or overwatching fires of terrain that's actually important for some reason.

 

The only reason we've gone into mountains in Afghanistan is because in an insurgency, PEOPLE are the key terrain. In a conventional high-intensity conflict, the strategic key terrain is ultimately centers of economic, industrial, and political importance. Operational key terrain is the transportation networks (roads, rivers, ports, airports) that let you move to those strategic centers, and that allow you to supply your forces as they move to those strategic centers. Tactical key terrain is those terrain features that allow you to control those lines of communication. Ergo, why fight in rugged forest and mountains? If the enemy hides there, you isolate and bypass. They're no longer part of the war unless they come out and fight... and if they do, they're doing it on your terms, out of the difficult terrain.

 

So, ok, a counterinsurgency light weapons carrier "mech" for mountainous terrain, sure (reference my first post on page 1; I think most of the disagreement between me and you has been semantics- I consider a "mech" to be the 40+ ton walking tank surrogates; what you're talking about, I would consider "mules" or "weapons carriers"). Usefullness of a mech in high-intensity conflict or as an armour surrogate, not really. I think a traditional "mech" (the walking tank surrogate) is useless-too many inherent disadvantages outweighing just a few marginal improvements in mobility. But a walking jeep/weapons carrier has SOME, albeit still very niche, role.

Edited June 13, 2014 by OutOnTheOP

[OutOnTheOP]

Other way round. We ARE doing it already, modularity is not a "logistical nightmare". Nothing Mech specific there. Sorry, I guess somebody else argued with that...

 

That was my point; I was being sarcastic in response to Malleoulus' insistence that "modular weapons" was an advantage to mecha, and his subsequent backpedaling (when pointed out that it was a logistical nightmare) that what he meant was having multiple variants that shared a same common chassis to ease logistical requirements and spare parts... which is, of course, something we already do (as I pointed out in the Bradley chassis example)

Edited June 13, 2014 by OutOnTheOP

[OutOnTheOP]

...hmm, thinking about netfire: so you would agree with the other post that tanks/vehicles are at there height?

Enemy just use their netfire equivalent and use two spotters to take out a tank platoon... end of battle? Netfire wouldn't make a difference between a tank, vehicle or Mech, right? ...maybe the Mech could try dodging and sidesteppinf the missile? :taking cover:

 

There will always be a role for armour-protected firepower platforms. The role could be filled by mecha or tanks... tanks just do it cheaper, with less moving parts, more inherent advantages, and fewer inherent disadvantages.

 

I wouldn't say tanks are at the height of their evolution (if nothing else, active countermeasures will aid survivability), but yes: there are lots of weapons systems that can destroy tanks, so they are by no means the end-all of warfare; they are not unstoppable juggernauts. No, tanks can't dodge a decent missile or high-speed projectile, but neither can a mech, so it's a zero-sum game on that point- which is exactly what I've been saying: the "advantage" of superior "agility" doesn't actually confer any tactical advantage to the mecha. If it's still not fast enough to dodge the weapon (or deny a firing opportunity in the first place), who cares? Look at it this way: if I fire a bullet at you, does the bullet care if you're a world-class sprinter, or a fat slob? No, the bullet only cares if you can move fast enough to get out of it's way. A hit two millimeters further to the right is still a hit.

 

You'd have to be orders of magnitude faster acceleration to make a difference. The mecha doesn't offer that. What DOES matter is the sensors-versus-stealth fight. Since neither the tank nor the mecha can dodge a shot once it's been fired, what matters is who shoots first. Who shoots first is predicated on who sees the other first. Assuming equivalent sensors, the one spotted first is the one with a larger profile presented. The mecha has the larget presented profile. Ergo, tank shoots first. Tank wins.

Edited June 13, 2014 by OutOnTheOP

[OutOnTheOP]

If you look back, I wasn't the one to fire the first shot on the personal attack bs. In fact, if I remember correctly, the words used were: "you're just like one of these idiots in the US that keeps saying , "you're a racist" when you are losing an argument.". This was the point at which he got deep under my skin.

 

I didn't call you an idiot, I said your debate tactics were as bad as idiotic American political wags. And they have been.

 

That said, if you want to play the "he said, she said" game, do you think that your constant insistence that anyone who doesn't share your opinion is too stupid, scientifically backward, or a luddite left behind by your great vision, is somehow LESS offensive, or LESS prone to get under my skin?

 

You may be more insiduous in the way you phrase it, but your attitude has been consistent: if you don't think mechs are useful, you're stupid, just like the people who thought trains/airplanes/whatever were impractical were stupid. At least I say what I mean upfront.

Edited June 13, 2014 by OutOnTheOP

[ShuRugal]

Has ground loading been discussed? Kind of kills main idea behind mech...mobility.

 

yes, but it seems to be inconvenient to point out that the ground under the mech's foot would give out from bearing so much weight on a small footprint long before the fable super acceleration would be achieved.

 

I would call it agile. Cars/tanks are significantly faster than horses and humans, but can't accelerate nearly as fast.

 

at the fastest point of human acceleration (the first 3 seconds) a hundred meter sprinter can manage about 3.5m/s^2. An M1A2 manages about 1.25 m/s^2. So far you're thinking on the right track. However, as you've just pointed out, a human racer can accelerate faster than a horse, which is also a legged creature... so clearly the variable lies somewhere else... Could it be relative mass?

 

a human sprinter weighs anywhere between 140-180 lbs. that's 45 lbs per m/s^2. An Abrams weighs 60 tons, which gives us 96000 lbs per m/s^2. Measuring acceleration per ton, a tank is 2100 times more effective than a person.

 

If you can fit two to three mech "tools" on one transport vehicle, you reduce the need to have a platform for every possible scenario anticipated. One mech can replace any one piece of equipment at a time. Only in scenarios where you need all the possible scenarios at once will a shortage exist. Two vehicles (a mech transport and it's cache transport) versus 5 or more.

 

Please give me an example of a modern mixed-unit-combat situation where you won't need to use multiple weapons and tactical capabilities simultaneously.

[Malleolus]

yes, but it seems to be inconvenient to point out that the ground under the mech's foot would give out from bearing so much weight on a small footprint long before the fable super acceleration would be achieved.

 

 

 

at the fastest point of human acceleration (the first 3 seconds) a hundred meter sprinter can manage about 3.5m/s^2. An M1A2 manages about 1.25 m/s^2. So far you're thinking on the right track. However, as you've just pointed out, a human racer can accelerate faster than a horse, which is also a legged creature... so clearly the variable lies somewhere else... Could it be relative mass?

 

a human sprinter weighs anywhere between 140-180 lbs. that's 45 lbs per m/s^2. An Abrams weighs 60 tons, which gives us 96000 lbs per m/s^2. Measuring acceleration per ton, a tank is 2100 times more effective than a person.

 

 

 

Please give me an example of a modern mixed-unit-combat situation where you won't need to use multiple weapons and tactical capabilities simultaneously.

 

I'm still not suggesting total replacement.

[ShuRugal]

You also aren't describing any battlefield roles which they could fill better than anything already filling those roles.

[Exorcet]

at the fastest point of human acceleration (the first 3 seconds) a hundred meter sprinter can manage about 3.5m/s^2. An M1A2 manages about 1.25 m/s^2. So far you're thinking on the right track. However, as you've just pointed out, a human racer can accelerate faster than a horse, which is also a legged creature... so clearly the variable lies somewhere else... Could it be relative mass?

I was going to post the exact same thing.

 

To add, I can't outrun a car, which can pull .5 g accel (~5 m/s^2) on street tires.

 

http://www.motortrend.com/womt/112_0306_spdtest/photo_10.html

 

I'm not really buying the mech as being overly agile (dodging RPG's etc). Certainly not with current tech. Even with future technology I don't think the mech would fair much better than a wheeled vehicle. Squating is going to limited by gravity, and the bigger it is the slower it will squat, until it's so small it will be consumed by the blast if the RPG hits the ground (which would also take out legs on larger mechs). Accelerating in any direction is basically something any vehicle can do already, so at best a draw there, and we know tanks, etc don't routinely dodge bullets.

[Malleolus]

You also aren't describing any battlefield roles which they could fill better than anything already filling those roles.

 

I was hoping you'd understand I don't want it doing anything on the battlefield better, just be able to do multiple things well, as needed.

 

I was going to post the exact same thing.

To add, I can't outrun a car, which can pull .5 g accel (~5 m/s^2) on street tires.

 

http://www.motortrend.com/womt/112_0306_spdtest/photo_10.html

 

I'm not really buying the mech as being overly agile (dodging RPG's etc). Certainly not with current tech. Even with future technology I don't think the mech would fair much better than a wheeled vehicle. Squating is going to limited by gravity, and the bigger it is the slower it will squat, until it's so small it will be consumed by the blast if the RPG hits the ground (which would also take out legs on larger mechs). Accelerating in any direction is basically something any vehicle can do already, so at best a draw there, and we know tanks, etc don't routinely dodge bullets.

 

I'm not saying it's going to pull a Neo. I'm saying whereas wheeled/tracked vehicles have to pivot to change direction, a mech can literally sidestep behind cover. Or, WITH ENOUGH RANGE, step out of the way or twist out of the way, whereas a tank would have to absorb the blow.

 

A 12-14 foot mech at a whopping 40t, well above what it would realistically weigh (half that maybe), would be at 88psi. Heavy, but not ground breaking, and that's if you have human scaled feet.

Edited June 14, 2014 by Malleolus

[NineLine]

What if an alien space ship crashed on the planet, giving us tech to create transforming Mecha, then it would be totally viable...

 

[OutOnTheOP]

What if an alien space ship crashed on the planet, giving us tech to create transforming Mecha, then it would be totally viable...

 

 

LOL possibly THE worst example of a functional mech concept in the long, illogical history of mecha fantasy. If it were light enough to be a good air/spacecraft, it would have insufficient armour to make a good ground unit. Also, the rate of accelaration depicted would turn the pilots into a chunky red paste on the back of the cockpit :megalol:

[NineLine]

Dude.... alien tech...

[ShuRugal]

I was hoping you'd understand I don't want it doing anything on the battlefield better, just be able to do multiple things well, as needed.

 

it doesn't matter if it can do things better or the same. For it to be able to replace two battlefield vehicles, it needs to be able to perform two battlefield tasks simultaneously. It doesn't matter if it can be a tank OR a troop carrier with equal utility: if you need both on the same mission, you still have to send two vehicles.

 

 

 

I'm not saying it's going to pull a Neo. I'm saying whereas wheeled/tracked vehicles have to pivot to change direction, a mech can literally sidestep behind cover. Or, WITH ENOUGH RANGE, step out of the way or twist out of the way, whereas a tank would have to absorb the blow.

 

the useful engagement range of the average RPG is 200-300 meters. At 300 meters, your mech pilot will have almost exactly one second from launch to identify the threat, react to the threat, and dodge the mech out of the way. If we assume he gets a magical missile alarm that tells him where the shot came from the instant it is fired, he's still going to loose a third of that second in human reaction time. By the time the mech starts to dodge, it will have about 600ms to get out of the way.

 

At tank engagement ranges, you're going to have exactly the same problem, because you might be an order of magnitude further away, but the incoming fire is also an order of magnitude faster. If you're far enough away for it to take more than 1-2 seconds for the rounds to arrive, you're far enough away that a tank could drive its own body length anyway, so the tank can dodge as effectively as the mech anyway.

 

 

A 12-14 foot mech at a whopping 40t, well above what it would realistically weigh (half that maybe), would be at 88psi. Heavy, but not ground breaking, and that's if you have human scaled feet.

 

88 PSI? that's nearly identical to the pressure of a racing bicycle. Do me a favour, and try to run a racing bicycle on loose soil, tell me how far your get, how fast you do it, and how much your legs hurt after.

 

an Abrams, on the other hand, exerts 14psi ground pressure, which is why it can dump 1500hp into the ground and not just sit there digging a hole.

[Malleolus]

it doesn't matter if it can do things better or the same. For it to be able to replace two battlefield vehicles, it needs to be able to perform two battlefield tasks simultaneously. It doesn't matter if it can be a tank OR a troop carrier with equal utility: if you need both on the same mission, you still have to send two vehicles.

 

 

It will only play any one role at any given time. The idea is that you can use the mechs in place (to augment) of some other units. Instead of having to transport 100 of every vehicle you might need, transport 50 of each, then 50 mechs with their requisite cache. They can be mixed and matched as needed, reducing logistical nightmares.

 

 

the useful engagement range of the average RPG is 200-300 meters. At 300 meters, your mech pilot will have almost exactly one second from launch to identify the threat, react to the threat, and dodge the mech out of the way. If we assume he gets a magical missile alarm that tells him where the shot came from the instant it is fired, he's still going to loose a third of that second in human reaction time. By the time the mech starts to dodge, it will have about 600ms to get out of the way.

 

There's also TROPHY, ARENA, and IRON FIST. Having a 360* field of radar coverage is not a new idea, and we're shooting RPG's, not magic missile. Any of these countermeasures would be able to identify and eliminate magic missile too, and alert the pilot to the location the fire originated from.

 

At tank engagement ranges, you're going to have exactly the same problem, because you might be an order of magnitude further away, but the incoming fire is also an order of magnitude faster. If you're far enough away for it to take more than 1-2 seconds for the rounds to arrive, you're far enough away that a tank could drive its own body length anyway, so the tank can dodge as effectively as the mech anyway.

 

Not from a dead stop, and only if the tank is oriented in the direction that it can do so. This is the beauty of a side step, you can be fully commited but can move side to side without having to pivot.

 

 

 

 

88 PSI? that's nearly identical to the pressure of a racing bicycle. Do me a favour, and try to run a racing bicycle on loose soil, tell me how far your get, how fast you do it, and how much your legs hurt after.

 

Won't be a problem... because 90 psi is for a dirt bike, not a mountain bike or other human powered bike. Furthermore, at 12'-14', you're realistically looking at closer to 20-25t, or 44-47 psi. Plus, compaction increases resistance on all but the most loose terrain, so "sinking in" won't be quite as bad as you'd think.

Edited June 14, 2014 by Malleolus

[Sceptre]

IMHO, A mech wouldn't be much good on a modern battlefield, except maybe as a sort of exo skeleton for soldiers and possibly with a HMD similar to the Apache, that gives the soldier symbology in his eye and some sort of vision enhancing. The exo skeleton would help for lifting say, more guns or ammo than a normal soldier could carry, and running a lot faster.

But the idea of having a mech in a direct combat role just doesn't seem very practical to me.... it's a nice big target for Aircraft to spot and kill, and would not stand much chance against a tank. Against infantry? Alright, probably, but how well armoured would it be? I have no idea.

Just my opinion... of course, mechs don't exist so we have no idea what they would be like or if they would be worthwhile or not.

[Malleolus]

IMHO, A mech wouldn't be much good on a modern battlefield, except maybe as a sort of exo skeleton for soldiers and possibly with a HMD similar to the Apache, that gives the soldier symbology in his eye and some sort of vision enhancing. The exo skeleton would help for lifting say, more guns or ammo than a normal soldier could carry, and running a lot faster.

But the idea of having a mech in a direct combat role just doesn't seem very practical to me.... it's a nice big target for Aircraft to spot and kill, and would not stand much chance against a tank. Against infantry? Alright, probably, but how well armoured would it be? I have no idea.

Just my opinion... of course, mechs don't exist so we have no idea what they would be like or if they would be worthwhile or not.

 

Thank you!

[shagrat]

LOL possibly THE worst example of a functional mech concept in the long, illogical history of mecha fantasy. If it were light enough to be a good air/spacecraft, it would have insufficient armour to make a good ground unit. Also, the rate of accelaration depicted would turn the pilots into a chunky red paste on the back of the cockpit :megalol:

 

Well, assuming gravity and similar is no problem for a race that can do faster than light travel. The mass/weight etc. will be irrelevant... switch the antigrav on and project a metagrav vortex in the direction of travel... ok if we master that, we won't need armor, tanks or Mechs anyway :megalol: simply project a little black hole inside the enemy tank or soldier... ouch!!! But were drifting off in the direction of pure science fiction here. More Star Trek than Mechs. ;-)

[shagrat]

IMHO, A mech wouldn't be much good on a modern battlefield, except maybe as a sort of exo skeleton for soldiers and possibly with a HMD similar to the Apache, that gives the soldier symbology in his eye and some sort of vision enhancing. The exo skeleton would help for lifting say, more guns or ammo than a normal soldier could carry, and running a lot faster.

But the idea of having a mech in a direct combat role just doesn't seem very practical to me.... it's a nice big target for Aircraft to spot and kill, and would not stand much chance against a tank. Against infantry? Alright, probably, but how well armoured would it be? I have no idea.

Just my opinion... of course, mechs don't exist so we have no idea what they would be like or if they would be worthwhile or not.

 

Think about what would happen if you would remove the soldier from the exoskeleton and make it a semi autonomous drone.

Same weapons capability or more, more ammo, sensors can react directly not relying on a human. Just select tactics, prioritize targets and let the "Mech" do the rest. Without a pilot pain from hits also wouldn't matter and a four legged, more stable and powerful movement would be possible.

I could really imagine such a Mech or two in an infantry squad or platoon accompanied by a few surveillance drones to deliver a lot more heavy firepower in areas difficult for vehicles or tanks.

Just don't think huge! Think 10-15 tons and 3-4 meters high!

[ShuRugal]

Think about what would happen if you would remove the soldier from the exoskeleton and make it a semi autonomous drone.

Same weapons capability or more, more ammo, sensors can react directly not relying on a human. Just select tactics, prioritize targets and let the "Mech" do the rest. Without a pilot pain from hits also wouldn't matter and a four legged, more stable and powerful movement would be possible.

I could really imagine such a Mech or two in an infantry squad or platoon accompanied by a few surveillance drones to deliver a lot more heavy firepower in areas difficult for vehicles or tanks.

Just don't think huge! Think 10-15 tons and 3-4 meters high!

 

Taking the pilot out is probably the best idea in this thread. It doesn't matter if it's going to get skragged the first AT round it takes, so long as I know one of my battle buddies isn't going to have to die for it.

 

of course, mechs don't exist so we have no idea what they would be like or if they would be worthwhile or not.

 

We have this field of science call "engineering". With it, we can make astonishingly accurate predictions about all sorts of things mechanical, even if they've never been built and tested. I'll be doing just that in just a minute, if you care to stick around.

 

It will only play any one role at any given time. The idea is that you can use the mechs in place (to augment) of some other units. Instead of having to transport 100 of every vehicle you might need, transport 50 of each, then 50 mechs with their requisite cache. They can be mixed and matched as needed, reducing logistical nightmares.

 

Well, now you're talking numbers that make sense, I wonder If we could do that with a wheeled system...

 

 

 

 

There's also TROPHY, ARENA, and IRON FIST. Having a 360* field of radar coverage is not a new idea, and we're shooting RPG's, not magic missile. Any of these countermeasures would be able to identify and eliminate magic missile too, and alert the pilot to the location the fire originated from.

 

and any of these systems can be put on existing armored vehicles. Putting IRON FIST on a legged platform won't increase its performance.

 

 

 

Not from a dead stop, and only if the tank is oriented in the direction that it can do so. This is the beauty of a side step, you can be fully commited but can move side to side without having to pivot.

 

 

Alright, it's time we talk some hard maths on this:

 

A leg transfers energy to the ground by rotating through a portion of an arc. It functions as a lever. Linear force transfer (such as when you stand up from a crouch) is accomplished by having a segmented leg where one end rotates one way, and the other rotates another.

 

In the case of forward walking, where the entire leg operates as a single lever, the power transfer to the ground is mathematically identical to a wheel: we need a torque between the base of the lever and the body, and the leg then transfers that torque into the ground.

 

For a human-proportioned mech of 14' height (4.2m), you're going to have 7' (2.1m) legs (from hip joint to heel, human legs are roughly 50% of total height).

To accelerate a 20 ton (18000 kg) object at 3.5m/s^2, we use Force = Mass * Acceleration, and we see that you need to deliver 63,000 newtons (14,000 lbf) to the ground.

For a 2.1m leg to deliver that force, we need to produce 132,300 Newton Meters (97,579.5 ft lbs) of torque around the hip joint.

The Honeywell AGT1500

out of the Abrams produces 3,754 Nm (2,750 FtLbs) of torque at 3,000 RPM. To provide 132,300 Nm, we need to gear that down 35.25:1, giving us a max rotation at the leg of 85 RPM.

With a 2.1 meter leg, this gives us a maximum speed of about 1 km/min, or about 35 mph. In reality, the top speed will probably lose at least 10mph, depending on leg travel, because when the leg is at any angle other than perpendicular to the ground, the engine has to hold a portion of the mech's weight as well as provide motive power. I can do the math on that loss if your really want me to.

 

Alright, we're looking good so far, but we still need to check a couple things... Will it be able to stand up? Going back to what i said a minute ago, when standing, the leg behaves as a pair of levers turning in opposition to produce a linear force away from the hip, so this next part will be doing math on a pair of 1.05m levers. to lift against gravity, these levers will need to accelerate our 18,000 kg at more than 9.8 m/s^2. Let's work with 10 m/s^2, as it's a nice round number (though it would be a rather slow stand speed).

 

 

18,000 kg * 10 m/s^2 = 180,000 N (40,000 lbf)

Now, since we've got two legs to spread the load over, we can say that each leg only needs to provide 90,000 N of force

90,000 Nm on a 1-meter lever.

But, each leg consists of 2 levers which must both produce that torque at the same time, so our total torque per leg...

90,000 * 2 = 180,000 Nm.

 

Right, so to get out AGT1500 to output 180,000 Nm, we need to gear it down 47.95:1. This gives us an output rotation of 62.6 RPM, or 37.5 deg/s. To stand up from a full crouch would take about 2.25 seconds, and you're going to need a second gear to do it.

 

Now, let's look at range... The AGT1500 consumes about 18.2 l/min (4.8 gal/min) of fuel at full power. So at full power, it will need nearly 300 gallons of fuel per hour of operation. So, lets see how much fuel we can fit inside it...

 

Your 14' tall mech will have a torso measuring about 2.1x1.25x1 meters (2.625 M^3 volume). The engine measures 1.63x0.9x0.8 (1.17 M^3) meters. Assuming by some miracle we design a gearbox that is half that size, that leaves us with an internal volume of 0.875 M^3, about 200 gallons.

 

So, it can move at ~25 mph, accelerate a little better than twice as fast as a tank, has enough fuel capacity for 45 minutes of operation, but no room for a pilot or ammunition.

 

Meanwhile, that same engine moves a 60 ton tank at 45 mph for just under 2 hours, and brings a whole lot of hurt along for the ride.

 

 

 

Won't be a problem... because 90 psi is for a dirt bike, not a mountain bike or other human powered bike. Furthermore, at 12'-14', you're realistically looking at closer to 20-25t, or 44-47 psi. Plus, compaction increases resistance on all but the most loose terrain, so "sinking in" won't be quite as bad as you'd think.

 

sinking in isn't the problem. the problem is asking a tiny patch of dirt to hold 130 kilonewtons of transverse force. Protip: it won't.

Edited June 14, 2014 by ShuRugal

[shagrat]

Now consider a 4-6 legs spider like walker and remember that a walking animal/human actually controls a continuous fall when walking. In fact you tip the body mass in any direction, let gravity do the work and try to keep the center of mass from plunging down. So you only counter a part of the one G acceleration to the center of the earth, while using your energy to counter the rest. Muscles and sinews, even store the energy exerted by gravity trying to pull us down and uses it for the next step... that's what makes a walk or run very energy-efficient. A wheeled vehicle uses its energy to overcome inertia and then relies on minimum friction to not loose the energy. If it has to climb, get's slowed (braking) it loses the energy. Climbing for a walker also means putting more energy to gain height, I know... Now the interesting part is change of direction or a stop. Walkers can quickly change the direction in which they "fall" aka sidestep. When "braking" they can very quick store or dissipate the energy from inertia. A vehicle needs time burn the energy mostly by applying friction... ok modern hybrids use a system that stores energy from the braking process to a battery, but that's very special.

Also I said in my first or second post that I consider a semi autonomous drone, not a piloted "Battlemech" some 10 pages ago.

Science and engineering have a bit of a quarrel here. Science wants to try things and find out what's possible. Engineering tries to predict and plan, considering 99% of what can happen and is utterly confused when the 1% kicks it's ass.

See Fukushima Dai ichi as a perfect example. Engineers calculated, modelled and predicted all "realistic" outcomes, yet they simply forgot to put just one of the three redundant emergency generators in a high place where it could survive a water tide. Yes, nobody had thought an earthquake plus a tsunami could hit the coast on one of earths most hot volcanic/earthquake active regions.

Engineers always think they can cheat or outthink nature, just they forget"To err is human" you cannot calculate every eventuality and history so often showed that when science discovers new knowledge engineering will adopt that knowledge and built what was "impossible" before... submarine, flight, spaceships, radio, electricity, computers... whatever. Would you have asked a 16th century "engineer" building a cathedral, if he thinks it is possible to go to the moon, he would have proofed you stupid because nobody can build a rocket from stone and wood and horses cannot run through the sky! Even in the 19th century Engineers would have calculated the impossible odds to produce a steam engine to propel a spaceship, because it is too heavy.

And so on and so on.

The original question was not if it is possible to build a Mech! That was a given. It was what combat role could it take. With miniature fusion reactors, endo steel skeletons, myomer muscle bundles, lightweight ferrofibrous armor and high performance joint actuators the technical problems will be solved, leaving the question: what should we do with it?

I know what you want to proof, and you may be right, but the question was never IF it is possible to build a Mech with today's tech.

I guess we established a possible infantry support role, already and agree that a "walking Tank" makes not much sense... we should leave it at that, what do you think? We start going in circles and tend to be more and more emotionaly over a simple "what if"...

Edited June 14, 2014 by shagrat

[Exorcet]

Now consider a 4-6 legs spider like walker and remember that a walking animal/human actually controls a continuous fall when walking. In fact you tip the body mass in any direction, let gravity do the work and try to keep the center of mass from plunging down. So you only counter a part of the one G acceleration to the center of the earth, while using your energy to counter the rest. Muscles and sinews, even store the energy exerted by gravity trying to pull us down and uses it for the next step... that's what makes a walk or run very energy-efficient. A wheeled vehicle uses its energy to overcome inertia and then relies on minimum friction to not loose the energy. If it has to climb, get's slowed (braking) it loses the energy. Climbing for a walker also means putting more energy to gain height, I know... Now the interesting part is change of direction or a stop. Walkers can quickly change the direction in which they "fall" aka sidestep.

Quickly is a relative term. How fast you can sidestep depends on geometry. The mech will probably be optimized for one direction, unless it doesn't need to be very quick. In directions other than the primary, it will likely be slower. Mechs also need to deal with their inertia when turning while on the move. Runners turn like a vehicle do, gradually changing their direction of motion. Only when you're still or at low speed can you easily sidestep.

When "braking" they can very quick store or dissipate the energy from inertia.

Only a portion. They may also give away their intentions when doing so.

 

A vehicle needs time burn the energy mostly by applying friction

This is no different than the mech. The wheeled vehicle has a potential advantage in being able to very finely control what does what while slowing down. The load on brakes con vary infinitely.

 

Also I said in my first or second post that I consider a semi autonomous drone, not a piloted "Battlemech" some 10 pages ago.

Science and engineering have a bit of a quarrel here. Science wants to try things and find out what's possible. Engineering tries to predict and plan, considering 99% of what can happen and is utterly confused when the 1% kicks it's ass.

See Fukushima Dai ichi as a perfect example. Engineers calculated, modelled and predicted all "realistic" outcomes, yet they simply forgot to put just one of the three redundant emergency generators in a high place where it could survive a water tide. Yes, nobody had thought an earthquake plus a tsunami could hit the coast on one of earths most hot volcanic/earthquake active regions.

Engineers always think they can cheat or outthink nature, just they forget"To err is human" you cannot calculate every eventuality and history so often showed that when science discovers new knowledge engineering will adopt that knowledge and built what was "impossible" before... submarine, flight, spaceships, radio, electricity, computers... whatever. Would you have asked a 16th century "engineer" building a cathedral, if he thinks it is possible to go to the moon, he would have proofed you stupid because nobody can build a rocket from stone and wood and horses cannot run through the sky! Even in the 19th century Engineers would have calculated the impossible odds to produce a steam engine to propel a spaceship, because it is too heavy.

And so on and so on.

The original question was not if it is possible to build a Mech! That was a given. It was what combat role could it take. With miniature fusion reactors, endo steel skeletons, myomer muscle bundles, lightweight ferrofibrous armor and high performance joint actuators the technical problems will be solved, leaving the question: what should we do with it?

I know what you want to proof, and you may be right, but the question was never IF it is possible to build a Mech with today's tech.

I guess we established a possible infantry support role, already and agree that a "walking Tank" makes not much sense... we should leave it at that, what do you think? We start going in circles and tend to be more and more emotionaly over a simple "what if"...

I don't agree with this. You are right in saying engineering isn't perfect, there are unknowns, and what is consider possible will change. This doesn't mean that you can go around and say that anything is possible though.

 

We don't have mini fusion reactors and high performance joints. You can't consider the argument without taking that into account. Why? Because how those systems work specifically will impact the mech and because how those system work will impact the mech competitions.

 

You could say that we may have technology advanced enough to allow mechs to fly supersonically in the future. This would allow mechs to dogfight, etc. Only jets will be better at it. Apply whatever raw power or drag reduction or advanced control systems to the plane instead of the mech and it would benefit more because it's better at the basics.

 

In short, we can't ask what we'll do with a mech unless we know how it will work. You can propose advantages, like saying it can jump over obstacles, etc, but then you have the problem of not knowing how well it can do this. That doesn't negate the point entirely, but it prevents you from saying it will be better than a wheeled vehicle with certainty.

 

Ultimately though I can agree with you in seeing potential in a infantry support mech.

[OutOnTheOP]

endo steel skeletons, myomer muscle bundles, lightweight ferrofibrous armor and high performance joint actuators the technical problems will be solved, leaving the question: what should we do with it?

 

Aaaand, you just totally lost me.

 

Quoting fictional technologies from Battletech (a fictional game in a fictional world) does NOT help back up the science of why it would work. I may as well say "we can have battlemages, because once we invent mana...."

 

Please, explains, what exactly IS "endo steel" (internal steel?). Or "ferrofibrous" (iron fiber? What is that, iron filings?) They aren't real technologies, they are technobabble names given to a fictitious science in a GAME. You really lose credibility when you reference fictional games to back up your science, because (true or not) it makes you look like you're arguing from a stance of fanboy-ism instead of cold rationality.

 

...and yes, I am a huge fan of the Mechwarrior PC games (3 is still the best!) and have several battalions of miniatures for the Battletech tabletop game. It's a cool game, and has a lot of "badass" factor to it, but that doesn't mean it's practical

Edited June 14, 2014 by OutOnTheOP

[shagrat]

Totally agree, I just wanted to point out, the OPs question was not about the technological feasibility, but the use case, so to say. Of course this is sci-fi stuff and fiction.

But when you would try to explain a nuclear powered submarine to an early 19th century steam machine engineer or operator it would have been "technobabble" for him ;-)

 

That was why the OP said something akin to: "imagine it would be possible to build a Mech"

[ShuRugal]

But when you would try to explain a nuclear powered submarine to an early 19th century steam machine engineer or operator it would have been "technobabble" for him ;-)

 

Thats an interesting choice of comparison. A nuclear power system is a steam engine. Your steam engineer/operator would understand it perfectly, once you say the words "Instead of coal, we generate heat with a newly-discovered process called "fission" that generates many times more heat than coal can." He would have to be educated on the dangers inherent in nuclear power, and the precise methods used to mitigate them, but he would not have to learn anything new for fully half of the system.

 

 

That was why the OP said something akin to: "imagine it would be possible to build a Mech"

 

Right, but my point here is that while may eventually be possible to brute-force a solution that makes mechs work on the battlefield, it will be possible to apply that same brute-power to a more efficient platform and have it work better.

 

The question asked by the op is "What combat role could a mech play on a real battlefield". The answer is "Several, but existing platforms would outperform it in most critical areas".

 

The only thing a mech can do that a tank can't is step sideways, and to gain that ability it gives up speed, range, and load-carrying capability. As I have rather thoroughly pointed out, a powerplant that could propel a 20-ton 4 meter mech at 25 mph for 45 minutes with no pilot or ammunition can (does) propel a 60-ton tank at 45 mph for 2 hours with a crew of 4 and enough ammo to fight half the day or more.

 

Give me a powerplant that moves a 60-ton mech at 45 mph, and I'll give you a 150-ton tank that can do 80 mph on the same engine. It's simple physics: I don't care what method you come up with to actuate the limbs, be it direct gearing, hydraulic, or sci-fi elasto-muscles, you still need to produce the same amount of torque to move the limbs, and producing that torque costs the same amount of power. a mech with 2m legs has (not accounting the need to hold itself up) the same power requirements for forward movement as a tank with 2m radius drive sprockets, and there's a good reason we don't build 'em like that.

[Malleolus]

We have this field of science call "engineering". With it, we can make astonishingly accurate predictions about all sorts of things mechanical, even if they've never been built and tested. I'll be doing just that in just a minute, if you care to stick around.

 

 

 

 

Alright, it's time we talk some hard maths on this:

 

A leg transfers energy to the ground by rotating through a portion of an arc. It functions as a lever. Linear force transfer (such as when you stand up from a crouch) is accomplished by having a segmented leg where one end rotates one way, and the other rotates another.

 

In the case of forward walking, where the entire leg operates as a single lever, the power transfer to the ground is mathematically identical to a wheel: we need a torque between the base of the lever and the body, and the leg then transfers that torque into the ground.

 

For a human-proportioned mech of 14' height (4.2m), you're going to have 7' (2.1m) legs (from hip joint to heel, human legs are roughly 50% of total height).

To accelerate a 20 ton (18000 kg) object at 3.5m/s^2, we use Force = Mass * Acceleration, and we see that you need to deliver 63,000 newtons (14,000 lbf) to the ground.

For a 2.1m leg to deliver that force, we need to produce 132,300 Newton Meters (97,579.5 ft lbs) of torque around the hip joint.

The Honeywell AGT1500

out of the Abrams produces 3,754 Nm (2,750 FtLbs) of torque at 3,000 RPM. To provide 132,300 Nm, we need to gear that down 35.25:1, giving us a max rotation at the leg of 85 RPM.

With a 2.1 meter leg, this gives us a maximum speed of about 1 km/min, or about 35 mph. In reality, the top speed will probably lose at least 10mph, depending on leg travel, because when the leg is at any angle other than perpendicular to the ground, the engine has to hold a portion of the mech's weight as well as provide motive power. I can do the math on that loss if your really want me to.

 

Alright, we're looking good so far, but we still need to check a couple things... Will it be able to stand up? Going back to what i said a minute ago, when standing, the leg behaves as a pair of levers turning in opposition to produce a linear force away from the hip, so this next part will be doing math on a pair of 1.05m levers. to lift against gravity, these levers will need to accelerate our 18,000 kg at more than 9.8 m/s^2. Let's work with 10 m/s^2, as it's a nice round number (though it would be a rather slow stand speed).

 

 

18,000 kg * 10 m/s^2 = 180,000 N (40,000 lbf)

Now, since we've got two legs to spread the load over, we can say that each leg only needs to provide 90,000 N of force

90,000 Nm on a 1-meter lever.

But, each leg consists of 2 levers which must both produce that torque at the same time, so our total torque per leg...

90,000 * 2 = 180,000 Nm.

 

Right, so to get out AGT1500 to output 180,000 Nm, we need to gear it down 47.95:1. This gives us an output rotation of 62.6 RPM, or 37.5 deg/s. To stand up from a full crouch would take about 2.25 seconds, and you're going to need a second gear to do it.

 

Now, let's look at range... The AGT1500 consumes about 18.2 l/min (4.8 gal/min) of fuel at full power. So at full power, it will need nearly 300 gallons of fuel per hour of operation. So, lets see how much fuel we can fit inside it...

 

Your 14' tall mech will have a torso measuring about 2.1x1.25x1 meters (2.625 M^3 volume). The engine measures 1.63x0.9x0.8 (1.17 M^3) meters. Assuming by some miracle we design a gearbox that is half that size, that leaves us with an internal volume of 0.875 M^3, about 200 gallons.

 

So, it can move at ~25 mph, accelerate a little better than twice as fast as a tank, has enough fuel capacity for 45 minutes of operation, but no room for a pilot or ammunition.

 

Meanwhile, that same engine moves a 60 ton tank at 45 mph for just under 2 hours, and brings a whole lot of hurt along for the ride.

 

 

 

 

 

sinking in isn't the problem. the problem is asking a tiny patch of dirt to hold 130 kilonewtons of transverse force. Protip: it won't.

 

All your math is flawed, when applied to a walking system. These things are true for tracked and wheeled systems (except the segwey), but not true for walking systems. Tracked and wheeled systems require power to be delivered constantly to both sides (with exception to pivoting the tracked system). This is not true for a walking system, especially a bipedal system. Bipedal systems use, primarily, 2 systems to decrease load requirements, or increase efficiency, that is not available to any other system. This is the inverted pendelum and off-center gravity, or "falling forward gait", as well as your muscles being compliant actuators. I will reference the most simple mechanical version we have for the majority of this, a series elastic actuator, but will mention the most appropriate at the end. First of all, we'll work off your following work:

 

 

 

"Now, since we've got two legs to spread the load over, we can say that each leg only needs to provide 90,000 N of force

 

90,000 Nm on a 1-meter lever.

 

But, each leg consists of 2 levers which must both produce that torque at the same time, so our total torque per leg...

 

90,000 * 2 = 180,000 Nm.

 

 

 

Right, so to get out AGT1500 to output 180,000 Nm, we need to gear it down 47.95:1. This gives us an output rotation of 62.6 RPM, or 37.5 deg/s. To stand up from a full crouch would take about 2.25 seconds, and you're going to need a second gear to do it."

 

 

 

Do something before you finish reading this: Stand up without leaning forward AT ALL. Back totally erect at 90*. Second time, stand up normally. The second time, normally, there's several things going on. You lean forward, inducing a momentum that builds the faster you throw your torso forward and the more you stand up. This momentum imparts, independent of your prime movers, a centripetal force on your hips and knees, which induces an assistive torque. The more you stand up, the less torque is required, which conveniently mirrors the loss in momentum. You use 50% less energy because of this momentum. For arguments sake, we'll say it takes 10% the weight of your upper torso to initiate this momentum gain in the torque load, and because you're not pivoting against a solid surface, both gravity and mass take over once your torso moves past 90* progressively building momentum until you begin to straighten out, reducing your momentum conveniently as your torque requirements diminish. So, right off the bat, unless you're doing squats in a mech, you're back to 90,000Nm. As previously stated, series elastic actuators increase any given actuators efficiency by including a compliant element in series with the actuator because of the, in this case, passive elastic compliant components spring constant, this efficiency gain being roughly 15%, meaning that the spring does 15% of the work usually. So, we're now sitting at 63,000Nm. So, now you can do two things, lower the draw from your power source, or increase the system forces. Still coming up short of your 180,000Nm by 30%, you have doubled either your load or your speed. Even with pretty bad friction losses, you can still come up short easily.

 

"In the case of forward walking, where the entire leg operates as a single lever, the power transfer to the ground is mathematically identical to a wheel: we need a torque between the base of the lever and the body, and the leg then transfers that torque into the ground.

 

For a human-proportioned mech of 14' height (4.2m), you're going to have 7' (2.1m) legs (from hip joint to heel, human legs are roughly 50% of total height).

To accelerate a 20 ton (18000 kg) object at 3.5m/s^2, we use Force = Mass * Acceleration, and we see that you need to deliver 63,000 newtons (14,000 lbf) to the ground.

For a 2.1m leg to deliver that force, we need to produce 132,300 Newton Meters (97,579.5 ft lbs) of torque around the hip joint.

The Honeywell AGT1500

out of the Abrams produces 3,754 Nm (2,750 FtLbs) of torque at 3,000 RPM. To provide 132,300 Nm, we need to gear that down 35.25:1, giving us a max rotation at the leg of 85 RPM.

With a 2.1 meter leg, this gives us a maximum speed of about 1 km/min, or about 35 mph. In reality, the top speed will probably lose at least 10mph, depending on leg travel, because when the leg is at any angle other than perpendicular to the ground, the engine has to hold a portion of the mech's weight as well as provide motive power. I can do the math on that loss if your really want me to."

 

No, it's not. Whereas wheels or tracks have to provide the running torque constantly on both sides, each leg on a bipedal system is only using running torque 50% of the time in a stiff actuator drive train, then you also have to include the phenomenon of "fall forward" gait and inverted pendulum. At most, with your math, it would only require this force on the first step, excluding, again, using your body this time (ankle to ground vs. ankle to head single order lever arm). Realistically, this takes a pitiful amount of initiating force to induce a cascade of momentum multipliers (head leading, arms, as well as shifting your center of mass over the balls of your feet rather than over the heels of your feet, hence why it's called falling forward), but in the end we can say that this is going to be 8-10%, experimentally (more like 15% theoretically), your anticipated torque requirement, with a system conservation of 20% after your forces play out per step. Your running torque just dropped to 78078 ft-lbs. Including the series elastic actuator rather than a stiff actuator, this decreases again to 62243.7ft-lbs. Basically, for the same power requirements, a bipedal locomotion can use 35% less the anticipated running torque of tracked or wheeled vehicles using proper gait and the most basic compliant actuator scheme, and only have to employ running torque on one half the entire actuator system per step. Not to mention all the mechanical advantage structures you could include.

 

On a side note this system is an endurance optimized bipedal locomotion system. Find me a tracked or wheeled robot of the same dimensions that can go over 14 miles on $.03USD of electricity and I'll delete my account.

 

"We have this field of science call "engineering". With it, we can make astonishingly accurate predictions about all sorts of things mechanical, even if they've never been built and tested. I'll be doing just that in just a minute, if you care to stick around."

 

In engineering we have these fields called mechatronics and biomechatronics that specialize in systems like this. We take the time to look into actuation and articulation schemes that lie well outside what conventional mechanical engineering is used to.

 

"Well, now you're talking numbers that make sense, I wonder If we could do that with a wheeled system..."

 

And how long does it take to exchange a package for another? A mech can theoretically do this on the order of minutes.

 

"sinking in isn't the problem. the problem is asking a tiny patch of dirt to hold 130 kilonewtons of transverse force. Protip: it won't."

 

If transverse forces were the only forces at play here, I'd agree. Furthermore, texturing the feet can increase both purchase and surface area.

 

I'm not questioning your intellect, nor am I going to say that I know that mechs can definitely play a significant enough role in the combat theatre to implement them immediately, but it cannot be proven yes or no until it is trialed. I am saying that you are attempting to analyze this system in a relatively 2 dimensional mindset, but it's extremely multi-dimensional.

Edited June 15, 2014 by Malleolus