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[Dwarf4Explosives]

So, I've started on a project to design a spider kaiju, and one of the subjects that I realized I would have to address is how it moves. The obvious way to go would be hydraulic pressure, which is what real spiders use, but then I got to wondering. I know pneumatic  are better for smaller movements and hydraulics are better for large ones, but is there a general rule of thumb that can be used for figuring out what substances would work even better at large sizes?

And, just to put things into perspective, the kaiju is about 525 meters long and 180 meters wide (including the legs, 500 meters wide), large enough to eat Godzilla whole.

[kaijyuu]

I was called?


Anywho with my limited knowledge of physics and the square cubed law, there's no way you could make something that big that used legs to travel. Treads are your best bet.

[acetech09]

So, I've started on a project to design a spider kaiju, and one of the subjects that I realized I would have to address is how it moves. The obvious way to go would be hydraulic pressure, which is what real spiders use, but then I got to wondering. I know pneumatic  are better for smaller movements and hydraulics are better for large ones, but is there a general rule of thumb that can be used for figuring out what substances would work even better at large sizes?

And, just to put things into perspective, the kaiju about 525 meters long and 180 meters wide (including the legs, 500 meters wide), large enough to eat Godzilla whole.

Hydraulics for those kind of things.

The problem with pneumatics is that air compresses - so if you're using it for, say, legs, you're going to have a decent amount of squishiness even under high pressure. Hydraulics is used in cranes, etc. because there is no 'give' due to fluid not compressing.

But yes, you'll need a nuclear generator and the only shot I see at even remotely making it possible would be carbon fiber and titanium composites.

engineer's 2c.

[Dwarf4Explosives]

It's a kaiju, so it's already at the far, far end of the realism scale, especially when concerning the ability to produce the appropriate materials. I was planning on incorporating some sort of nuclear generator into it's design as well.

And while I already know that hydraulics are a better choice than air (although the specific reason had escaped me), I'm also looking for alternatives to water that allow it to work better at such a humongous scale. Maybe non-newtonian liquids could provide some help with this?

[Levi]

Screw Hydraulics.  Wind power man, Wind power.

http://www.youtube.com/watch?v=HSKyHmjyrkA

[Dwarf4Explosives]

Yeah, but how exactly do you imagine wind moving a giant space spider? Solar wind might do the trick, especially on an atmosphere-less, magnetic field-less planet, dwarf planet or planetoid, but using wind power has the downside that you can't exactly control what the device/machine does in real-time; every move has to be planned for, and while that appeals to me on some level, it just isn't practical.

[Levi]

Oh, I didn't know it was an interstellar spider robot.   I got nothing then.

[Culise]

If it's interstellar, then you don't need to worry about the square-cube law quite as much.  Just never put it in a gravitational field where its weight will be sufficient to crush its legs (or if the legs are strong enough, whatever it is standing on).  I suppose the question is what kind of environments you anticipate this thing operating in, because that will play a large role in defining the design criteria necessary.

[Dwarf4Explosives]

Mostly medium (diameter of 50 km plus, so anything more than ten times its length) to large asteroids, along with dwarf planets and really, really small true planets (at most Mercury-sized in terms of volume), so gravity will be less of an issue than normal. The amount of force that it can exert is still important, however, which is the whole reason for this topic.

[acetech09]

It's a kaiju, so it's already at the far, far end of the realism scale, especially when concerning the ability to produce the appropriate materials. I was planning on incorporating some sort of nuclear generator into it's design as well.

And while I already know that hydraulics are a better choice than air (although the specific reason had escaped me), I'm also looking for alternatives to water that allow it to work better at such a humongous scale. Maybe non-newtonian liquids could provide some help with this?

Hydraulic fluid used in today's industry is typically mineral-oil based, with higher-stress applications being synthetic. In your application you can design a low-density synthetic hydraulic fluid that will reduce the effects of the square-cube law as much as possible.

[Mech#4]

You mean like the Monkey Lord in Supreme Commander? That's got six legs and a massive microwave laser stuck on top.

Also got huge exhausts so it looks like it runs on something like diesel or coal.

[Dwarf4Explosives]

Wait, if low-density fluid is useful, and since as much extra energy as possible is desirable, and photosynthesis produces hydrogen as a by-product...Would liquid hydrogen work ?

Hydraulic fluid used in today's industry is typically mineral-oil based, with higher-stress applications being synthetic. In your application you can design a low-density synthetic hydraulic fluid that will reduce the effects of the square-cube law as much as possible.

Back to seriousness, why would hydraulics or other fluid-based systems work better than pneumatics for large designs? The only possibly relevant factor I could think of is that gasses vibrate at high frequency, lowering their overall density, but your comment seems to imply that low density hydraulic fluids are best.

[andrea]

because of air compression, I guess. if you need a lot of force, and the tubes have an high volume, you need to do a lot of pushing to get any result.

[10ebbor10]

The advantage of fluid based systems is that fluids are much harder to compress. As such pressure distributes much easier through the system, and much more predictable.

[Dwarf4Explosives]

So would a system of small, solid (and lightweight) spheres work even better for pressure distribution?