HOW giant?!

[TransformerRobot]

I have read from an article that said Godzilla, as he is depicted, would not exist in real life because of the strains he'd have on his body from being 350 feet tall (150 in the original 1954 Godzilla).

 

Keeping that in mind, I looked into what the tallest dinosaur ever was, and it was Sauroposeidon at 18.5 meters (60.7 feet). The heaviest dinosaur, however, was Argentinosaurus at 77 tonnes (that's less than 17,000 pounds).

 

So what would be the tallest a giant monster could be in order for it to stand at 300 feet tall without collapsing? How would it be able to stay that way in real life?

[swansont]

There's a lot of factors in play. I suspect the argument about Godzilla is that it's too similar to a scaled-up T. rex, and you have structural problems because of the square-cube scaling: cross-sections are increasing with the size squared, but mass load goes up as size cubed. So pretty soon the support structure can't support the mass. Then you have bio+physics issues, like maintaining blood pressure and pumping blood, and how fast nerve impulses can travel, which probably affects locomotion and coordination.

 

So if something 350 feet tall existed, it would have markedly different proportions than something that was 20 feet tall, for the same reasons that creatures that are several feet tall are not the same structure as ones that are less than an inch.

 

You'll notice that Sauroposeidon and Argentinosaurus are both quadrupeds rather than bipeds. Four legs can support more mass than two, all else being equal.

[TransformerRobot]

Then what would be the cubic mass of a 120 foot tall bipedal robot made primarily of aluminum, able to travel a max of 100 km/h, and weighing 10 tonnes minumum?

 

(BTW I previously meant to say Argentinosaurus weighed 170,000 pounds)

[swansont]

Then what would be the cubic mass of a 120 foot tall bipedal robot made primarily of aluminum, able to travel a max of 100 km/h, and weighing 10 tonnes minumum?

I hope you don't really expect an answer to such a complex engineering problem, other than the trivial answer that a 10 tonne robot will have a mass of 10 tonnes.

[Enthalpy]

A giant sauropode could have had several hearts at different altitudes to obtain a decently even blood pressure everywhere. Nature hasn't done it from what I've read, but that would be an engineer's answer. Capillary action also permits trees as tall as Godzilla to live, but maybe it doesn't bring the throughput needed by an animal.

 

Weight of a 40m tall bipedal robot: I have no firm answer neither, because the robot can be built slim or sturdy. 40m is no big challenge for an aluminium construction, even a walking one. For instance airliners can be tall, and they have a big cabin over a tiny landing gear, so there's much engineering room left.

 

Or cranes. Their steel is less efficient than most aluminium alloys, and they can reach far over 40m.

[TransformerRobot]

Ah, mass is equal to weight, right? (I'm terrible with physics)

 

What if the robot had partly hollowed limbs made of steel, and was 200 feet tall? Would it be able to move easily without falling down? What kind of supports would it need?

Edited January 28, 2015 by TransformerRobot

[Greg H.]

Ah, mass is equal to weight, right? (I'm terrible with physics)

 

 

No. Mass is mass. Weight is a force normally defined as mass times the value of a gravity vector.

Though it's not surprising people get this confused - people in the United States tend to learn the Force measurement in one system (pounds) and the mass measurement in the other (grams, kilograms), and are taught early on how to convert between them, leading to the implication that they are measuring the same thing.

 

For example, your weight is 220 pounds. Your mass, assuming earth normal gravity, would be 6.837 slugs (not the garden variety).

 

In the metric system, your mass would be measured in kilograms, while your weight would be more appropriately measured in Newtons (IIRC).

 

Think about it like this:

 

If you go from earth to the moon, your weight will change. Your mass will not (unless you leave an arm behind or something).

Edited January 28, 2015 by Greg H.

[TransformerRobot]

With mass in mind then, what about this?

 

 

In this quick concept I did a second ago I have the robot's head and upper chest hollow to make room for a crew of 5 people, and the robot is only 72 feet tall.

 

With modern technology or tech in the near future would this be believable? I know it's not as exciting looking as Power Rangers or Pacific Rim, but still.

[Phi for All]

What reason is there to emulate the human form if you can't use it to access human structure? If we make a humanoid robot, isn't it because we want it to interact with everything we've built?

[TransformerRobot]

What reason is there to emulate the human form if you can't use it to access human structure? If we make a humanoid robot, isn't it because we want it to interact with everything we've built?

 

I'm speaking strictly for entertainment value, and to see what's possible in our lifetime with our current knowledge and technology. Isn't that one of the reasons we flew to the moon?

[Phi for All]

 

I'm speaking strictly for entertainment value, and to see what's possible in our lifetime with our current knowledge and technology. Isn't that one of the reasons we flew to the moon?

 

You asked if this concept was believable, not "possible". It's a Hollywood concept, one that looks cool and will probably play well, but engineering-wise it's a bust. A 72 foot tall bipedal robot has a poor center of gravity for a walking machine. Four legs, like the Imperial Walkers from Star Wars is much more practical.

 

There are great reasons to build a humanoid robot. If we want our machine to hand wash the dishes, walk up the stairs, mow the lawn with our lawnmower, run a race against humans, or drive a regular car, you build it to emulate the human form. Scaling the robot up twelve times normal removes this utility.

 

Of course, all you need to do is come up with a believable reason why it needed to be built this way. Since it's not practical mechanically, perhaps there's a symbolic reason for it to look like a huge person. I guess if it scares the enemy witless (for a time, at least) because it looks that way, it might justify the limitations the design enforces.

[swansont]

Current state-of-the-art for robots is probably the BigDog series from Boston scientific http://www.bostondynamics.com/robot_bigdog.html

 

They also have a Cheetah series for speed tests.

 

They are quadrupedal for a reason. Bipedal motion for large things is really hard to pull off. Even if that is assumed, the amount of stress you have to worry about will be tied in with the details of how the robot moves, which is largely unknown here. And the mass of a system will be related on what stresses the robot will undergo.

 

What I see is a request for a specific answer to a significantly under-constrained problem. One which has not been solved already — so you can't point to an existing object and compare — because the the cost/benefit ratio is too high.

[dimreepr]

Whilst I realise 30 meters falls a long way short of the required length in this thread; a water born animal, such as the Blue whale at 190 tonnes, is far more likely than a land born creature.

[TransformerRobot]

 

You asked if this concept was believable, not "possible". It's a Hollywood concept, one that looks cool and will probably play well, but engineering-wise it's a bust. A 72 foot tall bipedal robot has a poor center of gravity for a walking machine. Four legs, like the Imperial Walkers from Star Wars is much more practical.

 

There are great reasons to build a humanoid robot. If we want our machine to hand wash the dishes, walk up the stairs, mow the lawn with our lawnmower, run a race against humans, or drive a regular car, you build it to emulate the human form. Scaling the robot up twelve times normal removes this utility.

 

Of course, all you need to do is come up with a believable reason why it needed to be built this way. Since it's not practical mechanically, perhaps there's a symbolic reason for it to look like a huge person. I guess if it scares the enemy witless (for a time, at least) because it looks that way, it might justify the limitations the design enforces.

 

Well what about the AT-ST? Surely that's at least possible in real life too? It's not even as big as most giant robots in fiction anyway.

[Phi for All]

 

Well what about the AT-ST? Surely that's at least possible in real life too? It's not even as big as most giant robots in fiction anyway.

 

What about it? It's bipedal, but not humanoid. It's got a better leg design for bipedal locomotion, better balance. It's a HumVee with ostrich legs, nothing like a human.

 

And again, I was addressing the "believable" part, not the "possible" part. For me, the only legitimate reasons for a robot that looks like us is either to mimic us, scare us, or to use our tools. The AT-ST seems like a good fit if you want mobility in an area where terrain varies greatly, but scale it up six times bigger and you lose most of your ability to deal with terrain changes. Or to put it another way, if I need a 100 foot tall AT-ST to deal with my enemies, I'm probably going to build a big old bomb instead (or a planet killing death ray).

 

Hey, how about designing your big humanoid robot but remove the flaws inherent in a quadrupedal design that now walks upright? Without losing too much in form, you should be able to give him the AT-ST legs. Smaller head for better balance? That sort of thing.

[TransformerRobot]

Yes, but I was thinking more about recreating the whole "giant robots fighting giant monsters" scenario that made Power Rangers famous.

[Phi for All]

Yes, but I was thinking more about recreating the whole "giant robots fighting giant monsters" scenario that made Power Rangers famous.

 

Oh. I thought you were going for believable. My bad.

 

How about giant monster robots? A bipedal design with ostrich legs and a tail for balance, like a velociraptor, but with longer and more dexterous arms? You can still have your human operators in their places (but the guy in the head gets a much cooler cockpit). It could represent Earth as one of our most badass historical fighting forms, against the giant monsters from another planet.

[TransformerRobot]

I know those designs would work for extra balance, but I'm still trying to figure out how a biped like the Megazords would play out.

 

To be fair, Power Rangers is full of things that defy our current understanding of physics, like turning into costumed heroes at the press of a button or trapping the heroes in a storybook (see "Storybook Rangers" from season 2).

 

Even more baffling is that, at least according to the Power Rangers wiki, the original Megazord weighed 570 tons while standing 134 feet tall, yet it could move easily enough to fight each episode's monster of the week. Purely TV physics, or could a more scientific approach have been used to get around this?

[Enthalpy]

The biggest current airliners weigh not far from 570t and their tyres have far less contact area than the sketched feet, so the robot could stand on a landing track. A soft terrain would be more difficult. I suggest thick and highly damping shoesoles to reduce the shocks on the robot and on the ground.

 

For balance, the robot could have very long feet, rest on their complete length but walk or jump on their tips, like kangaroos do. A tail could help.

 

For the 24m tall robot of post #8, let's imagine it has a 2mm thick steel skin (ariliners would have aluminium or carbon instead, and you might rather consider a bulletproof fibre like aramide on a foam). 1500m² skin then weigh 24t, with the skin stiffeners 50t, with some skeleton possibly 200...500t, so the crew could be bigger. 500t *4g on one 2m*2m foot press 0.5bar which is comfortable. A 5t*1.5g elephant presses 5bar on two D=0.3m feet and fits varied dry terrains.

 

We have already built mobile machines much bigger and for bad terrain, cute examples:

http://de.wikipedia.org/wiki/Datei:Bagger-garzweiler.jpg

http://en.wikipedia.org/wiki/File:Garzweiler_Tagebau-1230.jpg(check the bulldozer for scale)

http://en.wikipedia.org/wiki/Bucket-wheel_excavator

http://de.wikipedia.org/wiki/Schaufelradbagger

 

In short: I've nothing against your sketch in post #8.

[TransformerRobot]

Well, as long as the 2 millimetre steel skin is strong then I'm all for it.

 

I was also thinking that maybe giving it special jet lifters in certain body parts for when it needs to regain balance.

 

I had already thought of the longer feet thing, I just neglected to show it in the sketch. XD I've seen Power Rangers do it lots of times, with the Megazord's feet usually enormous compared to it's hands.