Plausibility check for a setting - Iron Giants

[Simon_Jester]

Side note: I wonder if these guys might experiment with actual turbines for wind? They'd be a lot less exposed, and could be placed lower to the ground while still extracting power. High wind velocity makes a many-bladed turbine more practical.

Maybe the richer towers could use this. If fact, it could be an argument as to why a rich community wouldn't need towers: the turbines can be concealed and shielded behind armored walls, with the winds being ducted from the outside through minimal slits in the walls.
Why only rich towers: a working, geared multi-bladed turbine is going to use up a lot of metal and precision craftsmanship to be constructed than a simple windmill.

I'm honestly not sure you'd need gearing. It depends on the details- in real life, warships of the early 20th century were powered by turbines that were NOT geared in any way; the steam drove the turbine which directly drove the propeller shaft.

A quadcar can mount a much larger cooling system for the rider than an armored suit can, so there's another argument for its use. Though to see huge armored beasts cycling around on this thing strikes me as bizarre:

So find a more rugged, manlier-looking version.

I realized something this morning too: Going at 200km/h, an iron giant in a full, heavy suit of armor (10 tons) has about 15MJ of kinetic energy. Ramming an opponent might lead to mutual suicide, and these things are going to plough through walls.

They have too much surface area to go through a thick wall very well. Look up the sort of barriers they use to stop a truck bomb; a large truck going full tilt has about that kind of impact energy.

Here's another funny calculation: How far would a giant be able to slide of a metal surfboard?
I used this table of values, and came up with the result: 385-765m depending on the surface. Could it be that with a good enough run up, the giants could slide their way over all the potholes?

Solution: dig wider potholes.

Clown shoes won't help
What we need is something akin to a snowshoe, but modified for running by trimming the extension behind the heel and curving the front. Also, the legs are in contact with the ground for approximately 0.09 seconds. Just how much time does the sand have to slide away?

Enough for you to slip and fall on your ass? I'm not sure about this, mind, but I think I believe it. Try running over a floor sown liberally with marbles and you'll see what I mean. Basically, if the surface you're running on shifts, it'll either bog you down tremendously, or you'll skid out of control.

D-Day!
The giants would use large sheets of metal to place over the rubble and walk on.

What's the coefficient of friction between iron feet and an iron floor?

If you can work metal in the requisite quantity this is a great idea, and largely nullifies the ability to crack the stones.

Once again, a rich man's thing. It reminds me of the current situation with materials such as titanium. Our cars would be super light and super strong if we used it, and many other things would be much more efficient... but it costs 30-100 times more than steel.

Yeah. Rebar just isn't a thing in medieval societies.

I'll try and put up a step-by-step construction timetable for a colony's defenses.
Also, the problem with a loose talus slope is that it'll just get blown away by the wind.

It'd be interesting to tell the story of the one little colony that found a natural cement deposit; that'd solve a lot of problems fast.

[krakonfour]

I'm honestly not sure you'd need gearing. It depends on the details- in real life, warships of the early 20th century were powered by turbines that were NOT geared in any way; the steam drove the turbine which directly drove the propeller shaft.

Nuclear centrifuges work at 10,000 rpm. Gears are needed.

They have too much surface area to go through a thick wall very well. Look up the sort of barriers they use to stop a truck bomb; a large truck going full tilt has about that kind of impact energy.

Yeah, I realize, it's just that when I imagine them fighting in the living quarters of a tower during an invasion, I see them walking through the walls and bashing each other through them... much like the recent superman movie. It would make for a pretty decor.

Solution: dig wider potholes.

They would be useful, but the board is already a few meters long to reduce ground pressure and avoid digging into the ground.
In fact, since friction is independent of contact area, the board can be really long and wide, sliding over the smaller potholes easily. If the pothole is big enough to be called a pot-ditch, they better be large enough so that they cannot be jumped over using a big-ass Ollie.

Enough for you to slip and fall on your ass? I'm not sure about this, mind, but I think I believe it. Try running over a floor sown liberally with marbles and you'll see what I mean. Basically, if the surface you're running on shifts, it'll either bog you down tremendously, or you'll skid out of control.

The thing is, the running giant is kicking the ground twice a second for less than a tenth of a second. I'm envisioning an effect similar to the Jesus lizard. What slides out the way faster than water?

What's the coefficient of friction between iron feet and an iron floor?

Well, a firmly placed foot of iron on an iron surface has a coefficient of 1.1, which is very high when compared to the 0.4-0.3 of the ground they were running on. If the foot starts sliding, it drops quickly to 0.15, which is similar to that of a tire on a very wet road.

It'd be interesting to tell the story of the one little colony that found a natural cement deposit; that'd solve a lot of problems fast.

Ability to create the strongest walls on the planet with minimal effort and time? The rich colonies would be lining up for it.

[Simon_Jester]

Nuclear centrifuges work at 10,000 rpm. Gears are needed.

In that case, you'd need them anyway, so the gear train isn't one of the disadvantages of a turbine.

[Also, a relatively crudely made turbine might still work; I wouldn't know]

Solution: dig wider potholes.

They would be useful, but the board is already a few meters long to reduce ground pressure and avoid digging into the ground.
In fact, since friction is independent of contact area, the board can be really long and wide, sliding over the smaller potholes easily. If the pothole is big enough to be called a pot-ditch, they better be large enough so that they cannot be jumped over using a big-ass Ollie.

If the board is that big, it also has pretty hellacious sail area, so doing an Ollie might be dangerous.

The thing is, the running giant is kicking the ground twice a second for less than a tenth of a second. I'm envisioning an effect similar to the Jesus lizard. What slides out the way faster than water?

Point. You'd have to talk to someone who knows biomechanics.

Well, a firmly placed foot of iron on an iron surface has a coefficient of 1.1, which is very high when compared to the 0.4-0.3 of the ground they were running on. If the foot starts sliding, it drops quickly to 0.15, which is similar to that of a tire on a very wet road.

If one is firmly planting one's feet to climb the iron plank over the rubble pile, one is apt to take a javelin to the chest. If one is doing it at a run, a coefficient of friction of 0.15 is not sufficient to allow a humanoid to climb a slope he cannot grip with toes or fingers. Not if the angle of the slope is greater than arctan(0.15), anyway. Call it about nine degrees.

It'd be interesting to tell the story of the one little colony that found a natural cement deposit; that'd solve a lot of problems fast.

Ability to create the strongest walls on the planet with minimal effort and time? The rich colonies would be lining up for it.

I wonder if you might see a town that lives on cement deposits, has no radioisotope mine, and relies on trade with other communities for survival.

[Sea Skimmer]

Nuclear centrifuges work at 10,000 rpm. Gears are needed.

In any realistic sense, such centrifuges must be electrically powered. Gearing them to a wind turbine would never actually work.

[krakonfour]

Nuclear centrifuges work at 10,000 rpm. Gears are needed.

In any realistic sense, such centrifuges must be electrically powered. Gearing them to a wind turbine would never actually work.

The Wind Turbine could drive a flywheel, then the flywheel, once spun up enough, would be geared to the centrifuge.

[Terralthra]

Nuclear centrifuges work at 10,000 rpm. Gears are needed.

In any realistic sense, such centrifuges must be electrically powered. Gearing them to a wind turbine would never actually work.

The Wind Turbine could drive a flywheel, then the flywheel, once spun up enough, would be geared to the centrifuge.

There are practical limits on how efficient a flywheel can be, relative to the angular momentum it's storing and the difference between input rotation and desired output rotation (and mass determines its angular momentum storage capability). Sea Skimmer may be implying that a flywheel sufficient to drive a centrifuge (which is massive itself, given that it has to be spinning a significant quantity of uranium) for enough time to work (if you stop in the middle of centrifuging, and wait for a significant period of time in between, you have to start over), must be a pretty impressively massive. In that case, frictional forces might prevent your weak-ass turbine from getting it going in the first place, or from storing enough angular momentum from an non-constant power source with frictional forces draining some of it as waste over time.

If you conversely plan to have the wind turbine drive a smaller flywheel, which then drives the gearing system, the gears themselves must be taken into account when it comes to size and angular momentum and frictional losses.

[krakonfour]

There are practical limits on how efficient a flywheel can be, relative to the angular momentum it's storing and the difference between input rotation and desired output rotation (and mass determines its angular momentum storage capability). Sea Skimmer may be implying that a flywheel sufficient to drive a centrifuge (which is massive itself, given that it has to be spinning a significant quantity of uranium) for enough time to work (if you stop in the middle of centrifuging, and wait for a significant period of time in between, you have to start over), must be a pretty impressively massive. In that case, frictional forces might prevent your weak-ass turbine from getting it going in the first place, or from storing enough angular momentum from an non-constant power source with frictional forces draining some of it as waste over time.

If you conversely plan to have the wind turbine drive a smaller flywheel, which then drives the gearing system, the gears themselves must be taken into account when it comes to size and angular momentum and frictional losses.

Yes, there are limits. Modern windmills achieve 40% efficiency. A realistic-for-the-setting 15% (Tip-speed ratio of 2) efficiency windmill is still far from weak-ass.

The blades have a similar strength to the long arm of the trebuchet. That's a 15m radius in 92m/s winds. Output 40MW. Tip speed is 600km/h, hub speed is 2Hz (I know that's a frequency, but it's the number of rotations per second, which can be multiplied by however thick the hub is).

[krakonfour]

In that case, you'd need them anyway, so the gear train isn't one of the disadvantages of a turbine.

[Also, a relatively crudely made turbine might still work; I wouldn't know]

You started a windy discussion with people new to this thread.

If the board is that big, it also has pretty hellacious sail area, so doing an Ollie might be dangerous.

Are you telling me... that rushing invaders have to be expert sand-skaters?

If one is firmly planting one's feet to climb the iron plank over the rubble pile, one is apt to take a javelin to the chest. If one is doing it at a run, a coefficient of friction of 0.15 is not sufficient to allow a humanoid to climb a slope he cannot grip with toes or fingers. Not if the angle of the slope is greater than arctan(0.15), anyway. Call it about nine degrees.

The angle of rest for a pile of rubble caused by a wall collapse or a sand-filled embankment is usually twice as steep. Then again, there's no reason the iron plank can't have some sort of grip-enhancing features to prevent sliding.

I wonder if you might see a town that lives on cement deposits, has no radioisotope mine, and relies on trade with other communities for survival.

I don't really see that as likely. First, colonies are settled because of a nearby nuclear deposit. Plus, if they don't have their own fuel supply, then powerful and established communities will group up and starve them out.
I think the only case where this could happen is when a colony that got rich from mining quicklime runs out of nuclear fuel, and finds it more profitable to develop its trade than go raiding or dig deeper.

Also, I worked out the actual nuclear fuel requirement.
Let's say a small community has 120 members. A large community has 2000, and a rich and powerful community has 30000 or so.
The resting, low temp daily life power generation of an Iron Giant in W(Thermal) is 20kW. There might be 20 dedicated warriors that are expected to go up to 300kW on average. The nuclear fuel requirement is therefore 1.7kg a day. Modern gas centrifuges require up to 220MJ per kg enriched, which is no problem for our 40MW windmill. Notice how the military/civilian ratio is 17%.
A large community might have 500 warriors, and is at the limit of what it can produce. It needs 12kg a day. The ratio has gone up to 25% because the surplus is needed to conduct rare raiding parties and to protect trade caravans.
A huge community would have a considerable military force to defend itself and raid for more fuel, pushing down costs. It might have a M/C ratio of 30% (9000) because of the multiple trading routes to be protected, the numerous raids and the requirement to send a number of warriors on joint operations with other members of a federation (or to backstab and win a war). Requirement is 208kg a day.

Remember though, that breeder reactors only need low-grade fuels to function as it is recycled internally. The enrichment ratio here is 4.5%.

[Terralthra]

There are practical limits on how efficient a flywheel can be, relative to the angular momentum it's storing and the difference between input rotation and desired output rotation (and mass determines its angular momentum storage capability). Sea Skimmer may be implying that a flywheel sufficient to drive a centrifuge (which is massive itself, given that it has to be spinning a significant quantity of uranium) for enough time to work (if you stop in the middle of centrifuging, and wait for a significant period of time in between, you have to start over), must be a pretty impressively massive. In that case, frictional forces might prevent your weak-ass turbine from getting it going in the first place, or from storing enough angular momentum from an non-constant power source with frictional forces draining some of it as waste over time.

If you conversely plan to have the wind turbine drive a smaller flywheel, which then drives the gearing system, the gears themselves must be taken into account when it comes to size and angular momentum and frictional losses.

Yes, there are limits. Modern windmills achieve 40% efficiency. A realistic-for-the-setting 15% (Tip-speed ratio of 2) efficiency windmill is still far from weak-ass.

The blades have a similar strength to the long arm of the trebuchet. That's a 15m radius in 92m/s winds. Output 40MW. Tip speed is 600km/h, hub speed is 2Hz (I know that's a frequency, but it's the number of rotations per second, which can be multiplied by however thick the hub is).

I'd really like you to show your work a bit better than you are. You're rattling off numbers, without any indication how you got there (what maths did you do to get from "15m radius blades in 92 m/sec winds = 40MW"?).

Wind turbines of the modern day which are an order of magnitude bigger than yours produce less than a quarter of the output you propose. If your argument is that your spins vaster and thus extracts more energy from the wind, you'd have to show that the materials engineering and turbine efficiency of your iron/industrial-age (more or less) giants are significantly better than information-age blade modeling and materials.

[krakonfour]

I'd really like you to show your work a bit better than you are. You're rattling off numbers, without any indication how you got there (what maths did you do to get from "15m radius blades in 92 m/sec winds = 40MW"?).

Wind turbines of the modern day which are an order of magnitude bigger than yours produce less than a quarter of the output you propose. If your argument is that your spins vaster and thus extracts more energy from the wind, you'd have to show that the materials engineering and turbine efficiency of your iron/industrial-age (more or less) giants are significantly better than information-age blade modeling and materials.

I got the figures from an online wind power calculator.
The power output comes from the 200mph winds which prevail in the setting.
15m was determined by the length of the trebuchet long arm, designed to withstand a great amount of tension, and can easily be concerted into windmill blades.

The TSR ratio is 2, which is the lowest possible, to reduce tip speeds.

[Sea Skimmer]

The Wind Turbine could drive a flywheel, then the flywheel, once spun up enough, would be geared to the centrifuge.

This will still lack the precision control required to make the thing work. Your talking about more like 60,000-100,000rpm, not 10,000 rpm here to make this work well and they must be very carefully spun up and down to avoid damage. Suddenly clutching them to a flywheel will result in horrible things happening.

You want a way to make nuclear fuel that exploits wind, I suggest breeding Pu-239 in reactors cooled by air ducted through them Windscale style. Then all the complex processes are chemical in nature. You might also be able to use gaseous diffusion, that just requires pumping if you had a way to make all the filter in mechanical terms.

[Simon_Jester]

If the board is that big, it also has pretty hellacious sail area, so doing an Ollie might be dangerous.

Are you telling me... that rushing invaders have to be expert sand-skaters?

Well, that and their most common quote will be "OH SHII---" as they try a stunt in their board, tip it up into the hurricane-force wind outside, and go ass over teakettle when the board destabilizes.

Alternatively, their sheer mass and weight keeps the board from flipping over... but also makes it nearly impossible to do stunts because the massive physical force on the board slams it down into the ground.

If one is firmly planting one's feet to climb the iron plank over the rubble pile, one is apt to take a javelin to the chest. If one is doing it at a run, a coefficient of friction of 0.15 is not sufficient to allow a humanoid to climb a slope he cannot grip with toes or fingers. Not if the angle of the slope is greater than arctan(0.15), anyway. Call it about nine degrees.

The angle of rest for a pile of rubble caused by a wall collapse or a sand-filled embankment is usually twice as steep. Then again, there's no reason the iron plank can't have some sort of grip-enhancing features to prevent sliding.

They'd better be pretty rugged since multi-ton people are using them. It's possible, but the grip-enhancement still won't work to prevent sliding reliably unless people take it slow... in which case they're apt to take a javelin in the chest while scaling the wall.

I wonder if you might see a town that lives on cement deposits, has no radioisotope mine, and relies on trade with other communities for survival.

I don't really see that as likely. First, colonies are settled because of a nearby nuclear deposit. Plus, if they don't have their own fuel supply, then powerful and established communities will group up and starve them out.

What if the town in question is a political adjunct to a larger and more successful community? You know, like real "colonies" in real life, which remain affiliated with a mother-country that enables their success even though they are economically 'incomplete' in their own right?

Such a town might well become a target for raiders (because it contains stockpiled radioactives and tools) while still being able to sustain its existence (because a large city has a vested interest in its survival).

I got the figures from an online wind power calculator.
The power output comes from the 200mph winds which prevail in the setting.
15m was determined by the length of the trebuchet long arm, designed to withstand a great amount of tension, and can easily be concerted into windmill blades.

The TSR ratio is 2, which is the lowest possible, to reduce tip speeds.

The main problem you have is that gusts will tend to make this happen to large wind turbines. Rotating at such speeds also means having very good bearings, which your guys can't make- that's a serious challenge, how to make a good set of ball bearings with crude technology.

[krakonfour]

Well, that and their most common quote will be "OH SHII---" as they try a stunt in their board, tip it up into the hurricane-force wind outside, and go ass over teakettle when the board destabilizes.

Alternatively, their sheer mass and weight keeps the board from flipping over... but also makes it nearly impossible to do stunts because the massive physical force on the board slams it down into the ground.

This whole skating thing is a final-approach method at best. They need to maintain a good speed from start to finish, so I'm seeing them running up and dropping on the board around 500m from the enemy, with a speed that starts at 200 and finishes at 50km/h.

A massive jump (5m high) will keep them in the air for 2.02 seconds and let them cross 112m at top speed, and 28m at minimum speed. Even a small hop (1m) will let them cross ditches 50-12.5m wide.

They don't need to do stunts though, just land correctly. As for massive physical force.... Gravity is the same for everyone.

On the side: "OH SHI-" will never be pronounced. What does it actually mean to giants that burp out balls of fire as their method of removing waste?

They'd better be pretty rugged since multi-ton people are using them. It's possible, but the grip-enhancement still won't work to prevent sliding reliably unless people take it slow... in which case they're apt to take a javelin in the chest while scaling the wall.

A surface like sandpaper with ridges a few cm high would certainly work. At worst, the attackers can put on special shoes for climbing. Or in fact, no, they could have skating shoes, which the pull off for the attack, then rip off to reveal the extra grip climbing/interior combat soles.

Now that I think of it, that much grip will be more effective in keeping the giant on the slope than the slope on the pile of rubble! Maybe the 'landing platform' slope should have a spiked underside to dig into the pile of rubble.

Speaking of how dangerous this whole thing is... well, historically, we used to place huge ladders up against a wall and climb to our deaths when defenders were waiting for us on top, shooting stuff at us and pouring boiling oil. Time and time again. Suicidal, right?

What if the town in question is a political adjunct to a larger and more successful community? You know, like real "colonies" in real life, which remain affiliated with a mother-country that enables their success even though they are economically 'incomplete' in their own right?

Such a town might well become a target for raiders (because it contains stockpiled radioactives and tools) while still being able to sustain its existence (because a large city has a vested interest in its survival).

That would be a pretty unique case, where the 'outcasts' forced to find their subsistence alone re-establish contact with the people that threw them out.
Not saying it would never happen. A more likely case is that the situation you described happens, but instead of a large city, they could buy the services of a trade federation.

The main problem you have is that gusts will tend to make this happen to large wind turbines. Rotating at such speeds also means having very good bearings, which your guys can't make- that's a serious challenge, how to make a good set of ball bearings with crude technology.

Interesting video.
Now, I have mitigate your fears by saying that:
The wind turbines used today have hollow blades 30-50m long. The ones I'm using are 15m of solid steel.
The tip speed might be 600km/h, but it is rotating at 2Hz at the hub. That's 120rpm. An oiled shaft might be enough to handle these speeds, with lubrication continuously dripping along the pipe.

Also, these giants have the technology to make uranium refineries running at much much higher rpm. Because they only need a few kg per week, the size and centrifugal forces are small, and thus manageable, but its still 10k rpm.

This will still lack the precision control required to make the thing work. Your talking about more like 60,000-100,000rpm, not 10,000 rpm here to make this work well and they must be very carefully spun up and down to avoid damage. Suddenly clutching them to a flywheel will result in horrible things happening.

You want a way to make nuclear fuel that exploits wind, I suggest breeding Pu-239 in reactors cooled by air ducted through them Windscale style. Then all the complex processes are chemical in nature. You might also be able to use gaseous diffusion, that just requires pumping if you had a way to make all the filter in mechanical terms.

True, but this civilization has nearly no mastery of chemistry.
The main clutch here is that I don't need isotope separation. Since the giants have internal breeder reactors, they only need low-grade radioactive fuel, or even fuels we could consider as wastes today. Therefore, all the centrifuges have to do is separate common minerals from the much heavier radioactive elements. The difference in molar mass is hundreds of times greater.

PS: Anyone want to help with the second link in my signature?

[Simon_Jester]

On the side: "OH SHI-" will never be pronounced. What does it actually mean to giants that burp out balls of fire as their method of removing waste?

Very well, instead they will say "GREAT BALLS OF FIRE!" and wipe out.

One thing I think is a likely problem is that the dudes carrying all these giant surfboards and assault ramps and things will find the hurricane-force winds just picking them up and blowing them away, like papers in a stiff breeze.

Speaking of how dangerous this whole thing is... well, historically, we used to place huge ladders up against a wall and climb to our deaths when defenders were waiting for us on top, shooting stuff at us and pouring boiling oil. Time and time again. Suicidal, right?

Well, that sort of thing usually didn't work, unless you did it against an enemy you greatly outnumbered (not true here).

That would be a pretty unique case, where the 'outcasts' forced to find their subsistence alone re-establish contact with the people that threw them out.
Not saying it would never happen. A more likely case is that the situation you described happens, but instead of a large city, they could buy the services of a trade federation.

Given how rough an outcast band appears to have it according to you, I suspect that there will be a lot fewer of these outcast communities than you think. They just... have no realistic means of survival, if we buy into your basic premise of UBERLEET RAIDERS carrying masses of customized assault equipment being able to easily bust into their home base and murder them at will.

Interesting video.
Now, I have mitigate your fears by saying that:
The wind turbines used today have hollow blades 30-50m long. The ones I'm using are 15m of solid steel.
The tip speed might be 600km/h, but it is rotating at 2Hz at the hub. That's 120rpm. An oiled shaft might be enough to handle these speeds, with lubrication continuously dripping along the pipe.

I'm a bit skeptical at that point, among other things of how well the beam handles the centrifugal forces.

[krakonfour]

One thing I think is a likely problem is that the dudes carrying all these giant surfboards and assault ramps and things will find the hurricane-force winds just picking them up and blowing them away, like papers in a stiff breeze.

Once upon a time, Little Iron Giant invented hinges and made all the sh*t collapsible.

Given how rough an outcast band appears to have it according to you, I suspect that there will be a lot fewer of these outcast communities than you think. They just... have no realistic means of survival, if we buy into your basic premise of UBERLEET RAIDERS carrying masses of customized assault equipment being able to easily bust into their home base and murder them at will.

Oh they don't have it as rough as you think.
First off, they can survive for years without a gram of radioactive fuel. This gives them ample time to organize a raid or find their own mine. The problem is, if they fail, they run out of fuel, and if they don't, they've wasted many many years.
During their roaming years, they cannot eat metal or ingest active nanomachines to heal, but on the other hand, no-one bothers attacking them because they have nothing worth to steal.
Steal is the keyword here.
When the raiders manage to overcome the defenders, they do NOT go on a killing spree. Call it honor, call it survival logic when your population is so low, call it prevision for a future raid or whatever, but there are no massacres.
On the defender's side, there is no reason to die fighting too. They can live for years with nothing, and rebuild their fortress quickly. They just suffer, wait for the raiders to leave, and improve their defenses for next time.

Humm. One way to think of this is bullying. The big strong kids gang up on the weaker kids and extort money out of them. They don't however kill the snivelling children.

I'm a bit skeptical at that point, among other things of how well the beam handles the centrifugal forces.

I'll calculate the centrifugal force on a 15m steel rod going at 600km/h at the tip, 22km/h at the hub and tell you how thick it has to be in a bit.

[Simon_Jester]

One thing I think is a likely problem is that the dudes carrying all these giant surfboards and assault ramps and things will find the hurricane-force winds just picking them up and blowing them away, like papers in a stiff breeze.

Once upon a time, Little Iron Giant invented hinges and made all the sh*t collapsible.

[attempts to unfold big iron panel in windstorm]

["GREAT BALLS OF FIRRRRE!"]

[panel blows away]

Alternatively

[Attempts to surf on collapsible board]

[board buckles]

"GREAT BALLS OF FIRRRE!"

[goes ass over teakettle and smacks headfirst into the enemy's wall.]

I'm not saying it can't be done, mind you. But it's not easy, and there are real risks of screwing it up.
________________________________________________

Oh they don't have it as rough as you think.
First off, they can survive for years without a gram of radioactive fuel. This gives them ample time to organize a raid or find their own mine. The problem is, if they fail, they run out of fuel, and if they don't, they've wasted many many years.

This also suggests that they will trek a very, very long way to find a relatively desolate region before even thinking about creating a new base.

Alternatively, they will seek some place that has less population than it does carrying capacity, to piggyback off existing defenses and community alliances. Such places almost have to exist.

[Sea Skimmer]

True, but this civilization has nearly no mastery of chemistry.

Then harnessing nuclear power will be completely impossible by any means and your writing yourself into a giant pile of nonsense. You need advanced chemistry to make any of this work or else at the very least massive corrosion will destroy your reactor within weeks. All the more so if you don't expect to use a graphite pile which I highly doubt you'd want given the immense dry weight of such a device. Never mind the neutron embrittlement issue, the resistance of which is its whole own field of chemical coatings and steel alloy design. That's a huge problem since you want breeder reactors which are inherently based on exceptionally high levels of neutron activity and involve exotic coolants on top of it all. Water doesn't work right because it absorbs too many neutrons.

The main clutch here is that I don't need isotope separation.

You don't think you need the point of centrifuge enrichment, then why are you even talking about it?

Since the giants have internal breeder reactors, they only need low-grade radioactive fuel, or even fuels we could consider as wastes today. Therefore, all the centrifuges have to do is separate common minerals from the much heavier radioactive elements. The difference in molar mass is hundreds of times greater.

It would seem then that you do not understand how nuclear fuel is made. Centrifuge enrichment starts with uranium that has already purified and concentrated by milling processes, which are primarily a series of chemical processes though grinding into powder is also involved. This is all done at the uranium mine normally, producing yellow cake. More processes are used to then convert the uranium yellow cake into uranium hexafluoride gas which can then be run into a centrifuge or be subject to gaseous defusion or run into electromagnetic calutrons for enrichment to a U-235 level actually capable of working in a reactor. Then you process the fuel back into a solid form and make that into a fuel rod. That's mostly chemical processes too. Grinding up some uranium ore and spinning it down isn't going to work, the stuff needs to be dissolved to be pure. If it isn't near totally pure then look forward to your reactor melting down as soon as it powers on. That'd be cool, but not good!

Meanwhile breeder reactors are not never ending magic, they still build up impurities which must be removed via reprocessing the fuel in chemical processes, then refabricate the fuel rods. They make more fuel then they consume for around 100,000 years, but only if you keep reprocessing the fuel on a regular basis.

You don't get to do nuclear power reactors without serious chemistry. Even if we assumed the uranium in the ground is already nuclear fuel grade, which is not impossible on a planet with a shorter history then earth, you'll need it big time to get anywhere.

[Simon_Jester]

True, but this civilization has nearly no mastery of chemistry.

Then harnessing nuclear power will be completely impossible by any means and your writing yourself into a giant pile of nonsense. You need advanced chemistry to make any of this work or else at the very least massive corrosion will destroy your reactor within weeks.

They don't harness nuclear power, they eat it. Check the original post, these guys supposedly have a little reactor running in their guts.

Meanwhile breeder reactors are not never ending magic, they still build up impurities which must be removed via reprocessing the fuel in chemical processes, then refabricate the fuel rods. They make more fuel then they consume for around 100,000 years, but only if you keep reprocessing the fuel on a regular basis.

You don't get to do nuclear power reactors without serious chemistry. Even if we assumed the uranium in the ground is already nuclear fuel grade, which is not impossible on a planet with a shorter history then earth, you'll need it big time to get anywhere.

The basic premise is that the magic nanites which build the guys' physique handle the chemistry- they themselves do not know how to design industrial nuclear power plants.

Honestly I don't understand why krakonfour doesn't just say that the nanites also take care of the rest of the sifting process and these guys just eat yellowcake straight; it'd greatly simplify their ability to live in a realistic environment given their technology level.

[Sea Skimmer]

They don't harness nuclear power, they eat it. Check the original post, these guys supposedly have a little reactor running in their guts.

Doesn't really make any difference, a reactor is a reactor, he wants a plausibility check, pouring some nuclear powder into a vat or whatever inside a creature won't make a sustained but controlled chain reaction in any realistic sense. Nor does appealing to nanites remove the need for a steady supply of precursor chemicals for them to use in processes, unless they have magic to make it with out of nothing, or the neutron moderation requirements ect.. Nuclear reactors are all about balance, breeders absurdly so since they run very hot and it is very easy to slip below the threshold to transmute additional fuel, and yet also easy to go too far, which means you burn the fuel at the same time you make it and have the entire thing blowup in short order. Its plausible for nanites to act like say, DNA, but this is requiring moving some serious bulk materials some of which are absurdly reactive with each other. How does say, spent fuel get out of the reactor and get reprocessed inside the body without powering down the reactor?

Honestly I don't understand why krakonfour doesn't just say that the nanites also take care of the rest of the sifting process and these guys just eat yellowcake straight; it'd greatly simplify their ability to live in a realistic environment given their technology level.

Or better yet not even try to explain how it would work past 'atomic monster' that feeds on raw uranium ore and has a reactor organ. That would be a far better approach to take and little reach past what is apparently already being called for. Either that or at least switch to a reactor with liquid fuel and no breeder cycle attempt, which would be much more directly compatible with the idea of internal chemistry on a nanoscale. Then the liquid fuel could just be slowly leeched out and slowly replenished, which might be wasteful but very straightforward.

[Terralthra]

I'm a bit skeptical at that point, among other things of how well the beam handles the centrifugal forces.

I'll calculate the centrifugal force on a 15m steel rod going at 600km/h at the tip, 22km/h at the hub and tell you how thick it has to be in a bit.

How thick it is will change the centrifugal force. Force = ? * acceleration. Fill in the blank.

[krakonfour]

How thick it is will change the centrifugal force. Force = ? * acceleration. Fill in the blank.

If the blades are uniform in thickness, and 15m long, then we can model them as weight attached from a string midway. The average speed would be 300km/h, or 83m/s,
Iron has a tensile strength of 130Mpa, Steel has 200-250 MPa. That's 130-250kN/m2 depending on the material. Average density is 8000kg/m3, so we get these:
Centripetal force=15*X^2*Pi*8000*83^2/15=X^2*173139454
Resistance: 130 to 250*10^3*X^2*Pi=X^2*(408407 to 785398)

173139454 is not comprised within the ranges of Iron or Steel's Yield strengths, so a superior material or another solution is required.
Let's model then blade as a hollow tube. The Surface are would be the difference between the external R and the internal r. S=(R^2-r^2)*Pi

Let's imagine a half-filled tube, where R=2r

We get Cr=3X^2*173139454, and the resistance required is divided by 3 to X^2*57713151, which is still outside the range of Iron and Steel.
We can continue changing the ratio of the inner and outer diameters of the tube until we achieve a minimal ratio of 14 for steel and 20 for iron.

To find the actual radius, we have to calculate the centrifugal force. I used a calculator for this. The maximum blade mass Steel can handle is about 400kg, giving us a solid blade thickness of 3cm. That's very low, even if we made it hollow, meaning either the number of blades is very big, or shorter blades have to be used.

[krakonfour]

][attempts to unfold big iron panel in windstorm]

["GREAT BALLS OF FIRRRRE!"]

[panel blows away]

Alternatively

[Attempts to surf on collapsible board]

[board buckles]

"GREAT BALLS OF FIRRRE!"

[goes ass over teakettle and smacks headfirst into the enemy's wall.]

I'm not saying it can't be done, mind you. But it's not easy, and there are real risks of screwing it up.

Can't stop laughing. That's going in my sig.
I think I already did the calculation for the force the wind is putting on everything. A 3x0.5m rectangular board, even vertical, receives 11.4kN of pressure. Actually... that's at the limit of moving our Iron giant around.

This also suggests that they will trek a very, very long way to find a relatively desolate region before even thinking about creating a new base.

Alternatively, they will seek some place that has less population than it does carrying capacity, to piggyback off existing defenses and community alliances. Such places almost have to exist.

They need to cover area, not distance. It's like Minesweeper, making a long line won't help in finding anything. The second solution you propose is risky for the community that accepts them. What is stopping the outcasts from simply eating their fill and running away faster than any armored suit can catch up with them? And even so, what is the punishment? They won't kill them, and they sure can't regurgitate the nuclear fuel.

I guess there's a charitable soul somewhere, but I'm thinking Dark Ages ultra-isolationist, no foreigners allowed politics for the small communities, until they become big enough to force frequent trade and opening up.

[krakonfour]

They don't harness nuclear power, they eat it. Check the original post, these guys supposedly have a little reactor running in their guts.

True.
The main source of fuel is ancient nuclear reactors buried underground, thousands of years after humans have left the Earth, with the occasional 'high-grade' coming from the rarer nuclear warheads or intact cores.

The basic premise is that the magic nanites which build the guys' physique handle the chemistry- they themselves do not know how to design industrial nuclear power plants.

Honestly I don't understand why krakonfour doesn't just say that the nanites also take care of the rest of the sifting process and these guys just eat yellowcake straight; it'd greatly simplify their ability to live in a realistic environment given their technology level.

I'll think about that.
The main reason here for all of this is to give a reason for an energy source other than the giant's internal energy, and trade for what they make. I've made these giants too self-sufficient for their own good: they only need a few grams of nuclear fuel a week, and eat just about any metal and let the nanites handle the healing. How can war arise from this?!

[cadbrowser]

The main reason here for all of this is to give a reason for an energy source other than the giant's internal energy, and trade for what they make. I've made these giants too self-sufficient for their own good: they only need a few grams of nuclear fuel a week, and eat just about any metal and let the nanites handle the healing. How can war arise from this?!

Only a few grams of nuclear fuel a week? As big as these things are?

Consider establishing an upper limit for how many "thousands of years" has passed since humans have left the earth. How rare is this commodity? How many Iron Giants are there in the world? What is their rate of procreation/infant (?) mortality rates...etc.

How long before they run out of fuel? In respects to this finit supply...where are you introducing the timeline? This is important, because if this is an established "race" and your introduction to them is "well estimates put fuel reserves expiring in a million years"...then it won't be as facinating. However, if there is less than a decade of fuel left...then hell yes you are going to have wars.

[Simon_Jester]

They need to cover area, not distance. It's like Minesweeper, making a long line won't help in finding anything.

The point is that it's actively dangerous to stay anywhere near the community that just exiled you, so first you trek several thousand miles, then you find a place to settle by the usual means.

The second solution you propose is risky for the community that accepts them. What is stopping the outcasts from simply eating their fill and running away faster than any armored suit can catch up with them? And even so, what is the punishment? They won't kill them, and they sure can't regurgitate the nuclear fuel.

Actually, medieval communities weren't quite that isolationist. Among other things, disasters and wars tended to kill off the people, which left a lot of unworked land in need of new people, which in turn gave refugees a place to settle.

Not sure what the counterpart would be here. Do these guys ever get sick? I'm picturing some sort of exploding thermonuclear flu.