Zimbio/JJ DuncanThe scale of Pacific Rim is overwhelming. Giant monsters fight giant robots while being slammed with waves that appear to be hundreds of feet high. The combatants trample their way through major cities, while doing things like using an oil tanker as a baseball bat! When you see something like that, your brain tells you two things. First, this is awesome. Second, there's no way that's possible.
Confronted with these two thoughts, you can either suspend your disbelief and sit tight for what is most assuredly a very fun ride, or you can delve headlong into exactly why some of the things are possible and some of the things aren't. This is an exercise in the latter.
To assist in this exercise I reached out to a real-life mechanical engineer, my college roommate, Eddie Fishel, who seemed to ALWAYS be doing math whenever I wanted to do shots, but that's the difference between studying thermodynamics and studying journalism. Today he designs construction equipment like skid steer loaders for Case New Holland.
First, a word about the Jaegers just to give you a general sense of the scale, and the logistics of these things. In Pacific Rim, each country takes its defense in its own hands, each building a giant robot, or Jaeger, piloted by two soldiers tasked with fighting city-destroying monsters that have emerged from some inter-dimensional rift deep in the ocean. Much of the fighting takes place in or very near the water. They occasionally fight underwater. According to a blueprint released by Warner Bros as promotional material for Pacific Rim, the U.S. Jaeger Gipsy Danger stands 288 feet tall, and weighs 7,080 tons. This might help you get a sense of its size.
Gipsy Danger houses a nuclear reactor in its chest that is the source of most of its power, and is articulated by a complex system of hydraulic "muscle strands" that are each powered by a series of engine blocks. The reactor is cooled by seawater taken on through vents in the Jaeger's feet.
What follows are the thoughts of a real-life engineer when faced with this information.
1. Lifting an Arm Is a BIG Challenge
The Jaegers look incredible when they're throwing punches against a kaiju (the film's giant monsters), but just lifting one of those colossal arms would take an incredible amount of power. According to Fishel, "No current technology exists that would even hold the robot's arm up parallel with the ground. It wouldn't be able to move it."
I asked Fishel to help me calculate the amount of torque required to lift one of those arms (you know, assuming it's possible). He goes into some math at this point, but here's the breakdown.
Step 1: Calculate Arm Length (Based on human proportions)
- Arm length ≈ 40% of height
- 288 • 0.4 = 115.2 ft
Step 2: Calculate Arm Weight
- Arm weight is ≈ 6% of total body weight in humans, but let's assume these robots pack a little more punch, and arm weight is ≈ 10% of total body weight.
- 7,080 tons • 0.1 = 708 tons, or 1,416,000 pounds
Step 3: Calculate Torque Required to Lift Arm from Shoulder
- Assuming the arm has a uniform mass, the torque required to hold the arm up is equal to the weight acting at the center, multipled by the distance to the center. From here, let's say Torque=T. Here's how the equation looks given what we've just figured out.
- T=(115.2/2) • 1,416,000 = 81,561,600 lb-ft
That's a LOT of torque. This might help you understand it.
Fishel points out that the Bugatti Veyron, the world's fastest car, produces 922 lb-ft of torque. He also says the world's largest hydraulic motor produces 1,290,734 lb-ft.
"You would need 88,461 Bugattis or a little over 63 of the hydraulic motors just to hold the robot arm straight out at the shoulder," he says.
So hopefully if Earth is attacked by giant monsters it will be after we've figured out how to create a power supply and an engine capable of generating way more power than our current technology can provide. Otherwise, the battle might be over before it begins.
2. They'd Have a Hard Time in the Ocean
"Average ocean depth is 2.65 miles (14,000 feet), so these things would have to stay near shore, or be fully submersible. Engines need air and fuel to run, so if it's running engines to power the hydraulics for 'muscles' it can't go underwater unless it has massive air and gasoline/diesel storage tanks. Then consider the corrosion affects of saltwater, there are some processes that treat metal to be corrosion resistant for 500 hours in salt spray testing. But as anyone who's shipped metal that's not treated from China knows, it's covered in rust when it hits the port.
"Anyone who's stepped in mud can also attest that it doesn't support much weight, so I'm pretty sure these things would sink into the bottom of the ocean and crumble the concrete they stand on. Jumping and running or walking obviously increases the pressure too."
That last point about the ocean floor is especially pertinent if you factor in the steep drop-offs near some coasts. For instance, near the Golden Gate Bridge, which is seen being obliterated in the trailer for the movie. Near the pylons of the bridge, the depth is probably only about 10 or 15 feet depending on the tide, but if you pass one you'll quickly find yourself in the deepest part of the San Francisco Bay, with the floor up to 377 feet below the surface.
If a Jaeger found itself on one of these inclines, the soft soil under the water, which is constantly being churned by the strong currents that run through the inlet, would give, and the Jaeger would have an exceedingly difficult time just standing up, let alone fighting.
3. Oy My Knees!
Fishel writes: "No known materials would be able to support the stress of that much activity in the robot, especially in the joints. Consider how many people have knee and hip problems. These joints are under immense pressure in the human body when we're very active. High strength steel alloy has an ultimate strength of 760 MPa (megapascals) and carbon fiber has an ultimate strenght of 6,370 MPa. But if a robot is punching a monster, jumping, and running, the G forces created are big numbers. To show calculations on this would be very confusing (differential equations I haven't done since college). We deisgn for loads of 10 G's [10 times the force of gravity]. For the robot, that's 140 million+ pounds. Just roughly figuring it, the steel would need to be around 3 feet thick. (Please don't quote that cuz I'm not positive.)"
The final takeaway after talking to a real-life engineer? Just like you'd expect, the real-world physics of a functioning Jaeger don't really hold up. But don't see these as reasons why one couldn't exist. See these as reasons for the next generation of well-meaning, enthusiastic nerds to head to college and overcome the problems of extreme tensile stress, limited mobile power supplies, and how exactly you make a 7,080 ton robot walk in what would basically be quicksand to them. Then, maybe, our grandkids' grandkids will have the privelege of seeing one of these man-made monsters level a city block. Dream big, kids!