Why mecha?

[Previn]

You are seriously not getting multi-ton machines that fit through a doorway, so I'm also not sure why you're sending them 'crashing into buildings' when that's not something you expect of any armored vehicle. That's what you'd send power armored infantry or robots for, not mechs. You don't send a 70 ton, 60' tall mech into an office building doorway like an idiot.

Well, if you choose to ignore that I was talking about YOUR post that laid out the mech we were talking about as: "If posit that mechs are fast strike units, humanoid in form and between 10-12 tons and ~10; tall" I can't do much about that. But it makes a discussion work better if you don't spend your time setting strawmen on fire.

And then you added on going into buildings, which I didn't even imply. 10' tall is clearly NOT going to be doing that. The only straw men here are the ones you keep bringing.

[RadiantPhoenix]

I found some "specifications" for humanoid mecha from various works of fiction (Code Geass, Gundam, and Macross), assumed they had a footprint area equal to a rectangular approximation of one of my shoes scaled up to their height, and found the following values for ground pressure:

	Human	Gawain	Lancelot	Guren	Lancelot Albion	RX-78-2 Gundam	VF-1A
height (m)	2	6.57	4.49	4.51	5.15	18	12.68
mass (kg)	70	14570	6890	7510	9120	60000	18500
Pressure (kPa)	16	309	313	338	315	169	105
Pressure (psf)	334	6436	6516	7040	6556	3531	2194

(Mecha data from http://mahq.net/mecha/) (this ignores that the mecha in Code Geass generally keep both feet on the ground and push themselves along with wheel thingies that attach to their heels)

This document claims typical soil bearing capacities ranging from 2000 to 10000 psf, which seems to indicate that even the relatively high-pressure mechs that Code Geass has (they're the ones with over 6000 psf of pressure) would be able to support themselves walking on some non-exotic soils.

[kzt]

Exactly how does a 160 pound person exert a pressure of 334 PSF? Also the live load for a building by code is 50 PSF uniform with a peak of 320 PSF, so your example person would be over-stressing the floor standing in place. So something seems very odd here.

The figure I see for an adult male is 8 psi ground pressure (assuming no spike heels etc). So we'll say 25 square inches for a 200 pound person. So a 5 or so meter tall figure scaled up from a human would have about 156 square inches inches (2.5^2*25) of foot surface, or about 1.08 square feet. So it's one for the PSF basis.

9120kg is 20,100 pounds, so the Lancelot Albion per your chart would have a ground pressure of 20,100 PSF, or about 167 pounds per square inch. There is terrain that would be fine on, but it's not all terrain, or even most terrain.

If you look at figure 1 in this article you'll notice that the percentage of no-go terrain goes up fairly steeply as the ground pressure increases. The article only goes to 37 PSI, but it's pretty obvious that by the time you are at over a hundred PSI a huge percentage of terrain constitutes no-go areas. That includes obvious issues like bogging, but it also includes issues like not being able to climb a slope without the surface breaking down.

[Username17]

Exactly how does a 160 pound person exert a pressure of 334 PSF?

I know! I calculate 1152 PSF for a standing man.

Also the live load for a building by code is 50 PSF uniform with a peak of 320 PSF, so your example person would be over-stressing the floor standing in place. So something seems very odd here.

Uh... no. You are mixing PSI (pounds per square inch) and PSF (pounds per square foot). PSF numbers are over a hundred times what you are quoting.

As for PSI numbers, galloping horses exert 500 PSI on forward hooves. That is a lot. But you'll also note that galloping horses cross a lot of different terrains and it's not a huge problem for them.

If you look at figure 1 in this article you'll notice that the percentage of no-go terrain goes up fairly steeply as the ground pressure increases. The article only goes to 37 PSI, but it's pretty obvious that by the time you are at over a hundred PSI a huge percentage of terrain constitutes no-go areas.

That is for wheeled vehicles. A wheeled vehicle needs to be able to roll over each thing in its path. A legged vehicle can just step over. All of that "no go" terrain would not be no go to a legged mech. Just as it isn't no go to running deer.

-Username17

[RadiantPhoenix]

Exactly how does a 160 pound person exert a pressure of 334 PSF?

By having a contact area well under a square foot. 334 psf isn't that big.

Also the live load for a building by code is 50 PSF uniform with a peak of 320 PSF, so your example person would be over-stressing the floor standing in place. So something seems very odd here.

That might be the load after being spread out by a floor.

The figure I see for an adult male is 8 psi ground pressure (assuming no spike heels etc).

Which is over 1100 psf. 334 PSF is about 2.3 psi.

So we'll say 25 square inches for a 200 pound person. So a 5 or so meter tall figure scaled up from a human would have about 156 square inches inches (2.5^2*25) of foot surface, or about 1.08 square feet. So it's one for the PSF basis.

9120kg is 20,100 pounds, so the Lancelot Albion per your chart would have a ground pressure of 20,100 PSF, or about 167 pounds per square inch. There is terrain that would be fine on, but it's not all terrain, or even most terrain.

So, what's going on here is that we have different baselines for ground pressure. Your estimated ground pressure for the mecha is still 20 time your estimate for humans, you just have a higher value for humans.


Anyway, I took another look at the pictures, and was struck by just how big the feet on the mecha appear to be (compared to human proportions).

For example, the RX-78:


Appears to have feet that are at least 2m wide and 3m long, which would give it a ground pressure of around 2000 psf (14.2 psi)



The Lancelot Albion *looks* more normal in that regard, but I could be mistaken. (It does fly, though, so ground pressure is less of a problem)

[kzt]

Uh... no. You are mixing PSI (pounds per square inch) and PSF (pounds per square foot). PSF numbers are over a hundred times what you are quoting.

Nope. Building loads are not crazy high. You CAN build floors designed to allow 4 ton forklifts carrying 2 ton pallets to drive around, but that is most certainly not what a normal building floor can handle.

To quote a convenient site:
"The Uniform Building Code requires at a minimum, floors be designed to support the dead load of the floor and the required live load. For an office building, the live load is normally a uniform load of 50 pounds per square foot (PSF) over the entire tributary floor area for a framing member or a 2,000 pound load placed upon any 2 ½ x 2 ½ foot square space. The load producing the greatest stress in a framing member is the governing load for that member."

That is for wheeled vehicles. A wheeled vehicle needs to be able to roll over each thing in its path. A legged vehicle can just step over. All of that "no go" terrain would not be no go to a legged mech. Just as it isn't no go to running deer.

No, it's a paper discussing wheels vs tracks. It applies to all sorts of vehicles. Probably not 100% to legged vehicles, but there is going to be a high degree of correlation. And yeah, 160 pound deer can go places that 12,000 pound vehicles can't. Unless you are building a 160 pound 4 legged vehicle that isn't very useful to know.

[Prak]

Kzt, Frank's point is that if a legged construct sinks into the soil, it can step out of the pit it just created, just like you would in mud up to your ankles.

[kzt]

Kzt, Frank's point is that if a legged construct sinks into the soil, it can step out of the pit it just created, just like you would in mud up to your ankles.

You've walked though mud up to your ankles, right? How fast can you run in it? Consider trying to climb a steep hill covered with foot deep mud, will that work well? And being a large robot you can't even use the surface to get cover from the people shooting at you as you try to slowly struggle up the hill.

That is an example of a no-go area. It doesn't mean you can't possibly eventually get thought it, it means you can't effectively or reliably maneuver through it and you should avoid it. Particularly when people are planning on shooting at you as you try.

[Prak]

Um, no you can't run, but it would be a shit ton better than being stopped because you have wheels. A walking mech can walk through areas that would be no go areas for a wheeled or treaded vehicle of equal psi.

[kzt]

Perhaps. The main things that stop tanks are deep water, deep mud, tall walls and very steep slopes or lesser slopes covered with loose debris (like a talus slope).

I can see them handling taller walls than a tank, slightly steeper slopes and ones with debris (depending on your foot design) and possibly deeper water, but mud would still not work out well.

And if a walking mech has a lower ground pressure then a track it's a lot lighter too, which might well help.

[Previn]

Perhaps. The main things that stop tanks are deep water, deep mud, tall walls and very steep slopes or lesser slopes covered with loose debris (like a talus slope).

I can see them handling taller walls than a tank, slightly steeper slopes and ones with debris (depending on your foot design) and possibly deeper water, but mud would still not work out well.

Tanks also have problems with anything past light woods, or heavily broken terrain, bogs, swamps, or many urban areas where maneuverability is restricted and weapons fire can come from directions where tank is lightly armored and can't respond. When you start getting into things like heavy, or mountainous woods, you actually need engineers in to make roads for tanks.

[Silent Wayfarer]

Heavy Gear has powered armor sized mechs as the archetypical war engine. But they are mainly good for versatility. Tanks will tear them to pieces, and entrenched infantry in bunkers are very difficult for them to take out even with their dedicated antipersonnel armaments.

The depiction in HG seemed fairly reasonable to me.

Heavy Gear also uses drive wheels in the feet of their machines (~ 4-6 meters tall) so they can actually move fast on terrain which allows wheeled transit). Makes more sense than walking everywhere, and you can just lock the drive wheels and climb up inaccessible terrain.

More advanced gear-types also have hover-type drives, which is actually quite bad considering they live on a desert world with pockets of super corrosive sand scattered around (high maintenance), but the hover-equipped units are pretty much the fastest things on the battlefield save actual aircraft (which are again boned because lol sandstorms).

And yes, they made hovertanks. They were broken as fuck, in all senses of the word; hovertanks have a pathetic operational radius and need a lot of maintenance, but they're fast and maneuverable and carry a lot of armor for their size. They're not commonplace because they're literally the weapons of the alien invaders (Earth come to reclaim their colonies), not easy to reverse-engineer, very high-maintenance and don't have a lot of advantages on Terra Nova (the HG world).

[Avoraciopoctules]

The inline skates always felt kind of silly to me, but there's no denying that that they result in a major mobility increase. Gears are great because they can use cover and shrug off small arms fire. You can zip from behind one stack of crates to the next, taking a potshot at the enemy on the way and just ignoring any incoming fire from assault rifles.

Heavy Gear has some heavier mechs, but these generally use stabler nonhumanoid designs. Spider-bots and big rocket pods with legs, but no arms.

[kzt]

Tanks also have problems with anything past light woods, or heavily broken terrain, bogs, swamps, or many urban areas where maneuverability is restricted and weapons fire can come from directions where tank is lightly armored and can't respond. When you start getting into things like heavy, or mountainous woods, you actually need engineers in to make roads for tanks.

I've read some memoirs from armor vets in Vietnam, and seen pictures of what their vehicles did when busting jungle. Tanks are perfectly capable of forcing passage in pretty heavy woods or jungle. It's just kind of slow.

[Hicks]

That lower picture is from battletech. The centered mech is a Jenner, the left half out of frame is a battlemaster.

[Avoraciopoctules]

My mistake. I just googled "heavy gear fire dragon" and grabbed something else from the same photobucket album.

This should be an actual HG strider though:
http://images.dakkadakka.com/gallery/20 ... riders.jpg

[Juton]

That lower picture is from battletech. The centered mech is a Jenner, the left half out of frame is a battlemaster.

<Nitpick> The centre mech is not a Jenner but an Owens, the mech to the left is not a Battlemaster but a Crimson Hawk. </nitpick>

[Vebyast]

Long, skinny legs are bad. They need more armor per unit of useful volume, they're more likely to break under load (square-cube law), and there's no real benefit to going 100km/h. We simply don't have the materials science to build that thing, and we don't need to anyway: the Abrams is the fastest tank in the world and it still tops out around 50km/h.

The hexapod has much better topology and proportions, though it needs fine-tuning. The legs should be spread further out horizontally and should be angled further forward and back, to give them more range of movement. The torso should also be a single large rectangle-ish shape, kind of like what you see on modern MBTs. The back half will probably be some kind of modular bay for self-contained weapons systems; a couple of MLRS pods, or a couple of 155mm tubes, or a battery of 120mm mortars, or a pile of anti-tank guided missiles, or a big autocannon. Mechs are mostly artillery and infantry support because you simply can't armor up a mech enough for it to survive getting hit by a vehicle-mounted anti-armor weapon. There's a reason tanks are big boxes - it's about the most armor-efficient shape around.

---

Since Battletech has been brought up, I need to make a note about sensor and engagement ranges. Battletech's lostech assumptions had to be extreme to keep things on a tabletop. The IS seriously didn't even have EEPROM until the clans invaded. By comparison, modern targeting, gun-laying, and guidance systems mean that you can hit anything you can send a payload far enough to reach. The shortest-range weapons this thing will conceivably mount are light autocannon, and even those range out to 3km. 120mm mortars and 105mm howitzers go 10km, 155mm guns go more like 40km, and missiles go up to 300km. With GPS-guided munitions, laser designators, and IFF, if anybody on your side can see it, you can shoot it.

[Grek]

Vebyast's advice basically boils down to "make it more like a tank", which is completely useless since we have actual fucking tanks for any niche where "be more tank-like" is a valid suggestion. Mecha, if they ever do get brought into the military, will have some niche that isn't filled already existing vehicles. The big suggested one right now is urban artillery and fire support, so an actual spider mecha looks kinda like this:



Note how it has wheels on the bottom so that it can go fast like a car when there's good terrain, a smaller-than-a-car cockpit that can easily be hidden behind whatever cover is available on a city street and a half dozen long skinny legs for moving around on rough terrain that retract and bunch up against the hull when hiding in cover or using the wheels. It doesn't deal with anti-vehicle weapons by being armored enough to take the hit, it deals with them by being small and nimble enough to get into cover when one shows up.

[Previn]

Long, skinny legs are bad. They need more armor per unit of useful volume, they're more likely to break under load (square-cube law), and there's no real benefit to going 100km/h.

That's not how the square-cube law works. So long as you have the right strength material making up the legs, there is no danger of them breaking. If you make a person 4x as big, they have 8x the mass, but only 4x the muscle and no improved durability in their bones, meaning they have issues. If you make a robot that has 16x the strength of a human, and then scale it up 4x, and reduce the weight of materials or use empty space, the square-cube law is basically worthless besides telling you that it has a larger volume.

Since Battletech has been brought up, I need to make a note about sensor and engagement ranges. Battletech's lostech assumptions had to be extreme to keep things on a tabletop. The IS seriously didn't even have EEPROM until the clans invaded. By comparison, modern targeting, gun-laying, and guidance systems mean that you can hit anything you can send a payload far enough to reach. The shortest-range weapons this thing will conceivably mount are light autocannon, and even those range out to 3km. 120mm mortars and 105mm howitzers go 10km, 155mm guns go more like 40km, and missiles go up to 300km. With GPS-guided munitions, laser designators, and IFF, if anybody on your side can see it, you can shoot it.

The Battletech table top specifically doesn't model real ranges because they wouldn't reasonably fit on the table top, not as a concession to lost tech.

A NOTE ON SCALE AND THE RULES
Classic BattleTech turns represent ten seconds of real time, while each hex on a mapsheet represents thirty meters of a battlefield (for the exception, see Aerospace Movement, p. 74). However, players should note that such “real world” terms are abstractions when applied to the board game. Classic BattleTech is a game, not a detailed simulation. Therefore, the real world must take a back seat to game play—for simplicity, length of play, space required and simple enjoyment.

For example, while only a single ’Mech can occupy a hex, it does not actually take up the entire hex. A 30-meter-wide hex offers plenty of room for a twelve-meter-tall ’Mech to move around and avoid fire. In real-world terms, another ’Mech could easily fit in that space as well. However, for ease of play, a ’Mech tactically controls the hex it occupies even though it does not physically fill that space. Therefore, only a single ’Mech is allowed in a hex.

Weapon ranges provide another example. Players will quickly realize that the longest-range standard weapon in the game can only hit targets out to thirty hexes (900 meters) from the attacker. Real-world primary main battle tank weapons have operational targeting ranges in excess of 4,000 meters. Because Classic BattleTech mapsheets are only seventeen hexes long, recreating real-world ranges on a table would require more than seven mapsheets laid end to end, for a playing space greater than twelve feet in length. Not many people have that type of table space, nor would it provide players with any tactical maneuvering room. Anywhere a player might move a unit on the map, an attacker could hit that unit.

Even with that abstraction, you can use an optional rule for LoS ranges, allowing you to technically hit anything you can see with any weapon. If you look at the Mechwarrior RPG it has reasonable ranges for weapons in the BT universe. If you extrapolate from that, you get a standard IS Large Laser going about 4.6 miles as opposed to the .2 miles it goes in table top range.

Incidently, go go Myomer

[angelfromanotherpin]

I'm hoping it's a coincidence that looks a lot like the Wayne/Lex T-7.

[Juton]

The Battletech table top specifically doesn't model real ranges because they wouldn't reasonably fit on the table top, not as a concession to lost tech.

That's actually a retcon. Pre-clan invasion, in the real world (1986-1990?) the stated reason was that weapons had such a short range was because the inner sphere had lost the ability to maintain sophisticated targeting systems. Star League era tech was supposed to shoot for miles. The reason they had to change this was the Clans. The Clans where supposed to be more sophisticated then the Star League, so by the fluff they should be able to fire for miles, but they changed it so that games could still fit on the table top.

[fectin]

I'm just gonna leave this here:
http://www.kickstarter.com/projects/pro ... ng-robot-0


Also, a bunch of you need to stop and research what needs the military actually has. Just for the US, there are some huge differences in how the different services would use each type of mech you've proposed, and what roles they would fill.

[Previn]

The Battletech table top specifically doesn't model real ranges because they wouldn't reasonably fit on the table top, not as a concession to lost tech.

That's actually a retcon. Pre-clan invasion, in the real world (1986-1990?) the stated reason was that weapons had such a short range was because the inner sphere had lost the ability to maintain sophisticated targeting systems. Star League era tech was supposed to shoot for miles. The reason they had to change this was the Clans. The Clans where supposed to be more sophisticated then the Star League, so by the fluff they should be able to fire for miles, but they changed it so that games could still fit on the table top.

Well, I started playing BT in 1988, and I don't recall that at all. I do recall 'fire and forget missiles' and 'lasers with improved ranges' as being SL era tech that was lost though (which later ended up being Streak and ER-Lasers respectively). I'll dig up my original boxed sets, TRO 3025 and 2750 and check when I get home.

[Grek]

I'm hoping it's a coincidence that looks a lot like the Wayne/Lex T-7.

Given that I have no idea what either of those are, it probably is.