Walking machines.

[Peebo-T]

Sorry for 're-hashing' a topic that has been talked about before, but...

So a tank spreads its weight over its tracks.

They are also rather loud.

Hover craft spread their mass over their air-cushion.

They are also rather loud.

A wheeled vehicle is not as loud as either of the above, but it runs into other problems of its own.

My question is, how loud would a walking vehicle be? Other than the drone of its engines, would not the sounds of its 'feet' be quieter than tracked/hover machines? Even quieter than wheeled vehicles, perhaps?

So, where some sort of 'stealth' is needed, would that be a place to use a walking vehicle?

Edit: Also, sorry if this is the wrong forum for such question. Just think of Imperial walkers as examples?

[Ford Prefect]

You can only answer these sorts of questions by knowing stuff like the mass of the robot in question, the method behind driving its limbs, exactly what powers it and so on. It could conceivably be no louder than a running human, or it could be slightly less noticeable than Godzilla.

[Lord of the Abyss]

My question is, how loud would a walking vehicle be?

That's the sort of thing that depends very much on the technology involved.

So, where some sort of 'stealth' is needed, would that be a place to use a walking vehicle?

That would depend. Your classic giant-humanoid "mecha" is going to be terrible at stealth no matter how quiet; it's tall. Vehicles in general aren't going to be all that stealthy since they'll be bulky, to contain a human and whatever else. But some multilegged drone the size of a human or smaller might do well with legs. Stalking like a cat, or if small enough scuttling across the ceiling out of sight.

[Shroom Man 777]

So its having wheels or legs or treads will somehow have an effect on the sound of its engines? Giving legs to a turbine engine will somehow make it quieter?

[Purple]

You might want to check this out.
Link

It is a rather well done comprehensive study of the failings of walking vehicles. And while it talks a lot about armor and stuff I think some of your questions will be answered. Especially the Surface Area/Volume and Ground Pressure sections.

[Peebo-T]

*Bows* Thank you for your time and replies.

[Ford Prefect]

Ground Pressure sections.

Ground pressure is a load of crap. It's absolutely not a big deal: galloping horses exert 3-4MPa, a woman in stilettos will exert 13MPa. Main battle tanks are at about 100KPa, and yet they still rip up roads. There's way more to ground pressure than just ground pressure.

[Purple]

Still, I think that it does point out the obvious.
<metafore>Don't think a walker can climb stair cases just because its feet can fit on the steps.</metafore>

Also, tanks don't rip up roads because of high ground pressure. They rip up roads because you have a huge chain of metal links designed to crush rock and operate in rough terrain being ground into and through the road surface.

[Simon_Jester]

So its having wheels or legs or treads will somehow have an effect on the sound of its engines? Giving legs to a turbine engine will somehow make it quieter?

My question is, how loud would a walking vehicle be? Other than the drone of its engines, would not the sounds of its 'feet' be quieter than tracked/hover machines? Even quieter than wheeled vehicles, perhaps?

Shroomy, you let your smarm eat your brains again.

The OP specifically didn't say any such thing.

[Darth Tedious]

With regards to noise levels, I think it totally depends on the nuber of legs- an Imperial walker or humanoid mecha is going to thump quite loudly as it steps, where something akin to a millipede should be able to tread more quietly (even if it weighs the same). In addition, the chorus of 50/100/1000 little servos running lots of legs might well be quieter than a half-dozen MASSIVE ones running a pair of tremendous legs.

[Peebo-T]

*Nods* I was thinking of 'multi-peds' such as these incarnation.

Link

A legged vehicle might be quieter then a wheeled or tracked vehicle. So, if the purpose is to 'sneak' up on something....a possibility, yes?

*Bows* Again, much thanks for the replies.

[Dave]

A wheeled vehicle is not as loud as either of the above, but it runs into other problems of its own.

Can you be specific here? I think you're just handwaving this away. Because, see, as others have mentioned, legged vehicles have the sound of footfalls, and tracked vehicles have (to some extent) the sound of tracks shifting and moving against each other, but (smooth) wheeled vehicles don't have obvious mechanisms that might make noise. Especially at low speeds the noise generated by the 'rubber hitting the road' is basically negligible.

Might I remind you that electric wheeled cars of today have created concern that they are too quiet? I think, as other people have suggested, that powerplant noise is usually a greater factor than the noise created by the propulsion system.

[Ford Prefect]

Still, I think that it does point out the obvious.
<metafore>Don't think a walker can climb stair cases just because its feet can fit on the steps.</metafore>

I don't think you're getting my point. Ground pressure is one of those things that people latch on to in regards to giant robots like it's the proverbial Crucifix, but a woman in in stiletto heels has 170 times the ground pressure of a tank ... yet which one is going to go through the floorboards? Ultimately a giant robot is going to wreck things because it's actually heavy as opposed to because its ground pressure is high. I mean, horses don't go knee deep into dirt when galloping out on the rolling plains, and their ground pressure is massive. This isn't to say that ground pressure is irrelevant, but rather that it's being mistakenly given relevancy in literally every context or environment without any really deep reasoning as to why.

[Lord of the Abyss]

Because, see, as others have mentioned, legged vehicles have the sound of footfalls, and tracked vehicles have (to some extent) the sound of tracks shifting and moving against each other, but (smooth) wheeled vehicles don't have obvious mechanisms that might make noise.

Well, there's the sound of going over obstacles off-road. A walking machine or a person can just step over things a wheeled vehicle has to drive over. And I'd expect more noise on surfaces like gravel from a wheel than from something carefully picking its way across.

[Sea Skimmer]

How much noise a mech makes would depend on how big it is, how quickly it is moving at that given moment, how much precision the legs can actually adjust elevation and agle with, and on earth actually powers it in the first place. A hypothetical mech with artificial muscles powered by a super catalyst fuel cell might make little more noise then the sound of its feet touching ground and a slight hiss of exhaust gas which could be muffled if it was moving slowly and well lubricated.

On the other hand, anything remotely like what we know for certain could be built; artificial muscle on a large scale is very questionable, would need electric motors and hydraulic actuators. Both make a whole lot of noise, and even more so for the generator, hydraulic motor and all the cooling gear they’ll require to keep running. Some kind of gas turbine power plant is likely and a jet engine isn’t known for being silent, though quieter then a diesel of similar power. Mecha need high power to weight ratios, and all else being equal higher performing power sources are almost always noiser.

Almost all of this also applies to conventional vehicles. You also have the additional issue of equipment, spare parts or ammo that might be hanging on the mecha externally. Mechs have very shitty internal volume relative to overall size so odds are a lot of ammunition at the least will be in externally racks. That isn’t necessarily a bad thing for survivability either, but the gear shuffling around is going to make noise.

Probably the quiets vehicle you could get in a realistic situation would be something wheeled creeping on battery power and only running a hybrid engine in bursts when in defile. Wheels are pretty quite and produce a continuous noise which is less obvious to the human ear.

Hypothetical super mech moving with ultra precision in all movements and a perfect grasp of the terrain might be very quite… it would also be moving slow as hell and very tall. A metal mecha making a belly crawl meanwhile…. that’s going to make noise like a WW2 tank with all metal tracks only worse. A mech running would not only make a lot of noise, it would be at constant risk of bogging down. Then you need the other mecha to come by and dig you out with giant entrenching tools.

[Ford Prefect]

I suppose it's probably worth pointing out that JSTA's working RX-78 Gundam would have theoretically needed seven gas turbine engines, and thirty 400kW superconducting motors, to walk. While superconducting motors are relatively quiet, seven gas turbines aren't. I think they specified the type used in Apache helicopters, but I'm a little hazy on that. Certainly the RX-78 is a very large robot, and JSTA calculated that its likely mass would have been about 43 tons, but unless you're talking something pretty small, existing technology isn't likely to net you a quiet robot.