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Building a Great White Shark

Building a Great White Shark

Just the mention of the name Great White Shark is enough to send a quiver down the spine of the average diver. Also known as Carcharodon Carcharias, it can reach a length of 23 ft or more and weigh in at over 5,000 lbs. That's bigger than your typical SUV.

Yet little is known about this mysterious creature. To better understand the legendary Demon of the Deep, Fabian Cousteau (grandson of Jacques Cousteau) contracted my company, E.P. Industries, to design a "swimming lab" that would allow him to observe and study the Great White in its world. Our challenge: To construct a counterfeit shark that would contain a diver with a PRISM (digitally controlled closed circuit diving system), be self-powered (swimming by tail motion) and easy to steer, and look like a real shark. These specs were a significant leap over the decoy I developed in 1989 that was remotely powered through an umbilical cord connected to a shark cage. It ultimately met its demise in the jaws of a real Great White.

Essentially, we were being asked to design a giant, self-propelled mechanical shark in just four weeks.

Working under an impossibly tight timetable, I asked our animator, Dave Mansfield, to put together a quick animation showing the mechanical shark swimming with a diver inside. He grabbed a generic Great White shark mesh, loaded it into Discreet's 3ds max 5.0 modeling and animation software and scaled it to 14 ft. Then he started adding spline shapes for the ribs, adjusting each to fit. He created models for the air tanks and rebreather models from dimensions taken off of various diving websites.

Since a shark's natural movement is a sinusoidal wave, Dave used a wave space warp modifier to create the swimming motion. This way, he was able to quickly change the amplitude and frequency of the swimming motion of the entire model with only two key frames. He adjusted the attenuation of the wave space warp effect so that the head would remain relatively still while the body moved.

Dave rendered out several different passes of the shark, including the skin layer, the ribs, mechanics, and diver layer, and then composited them all together in Adobe AfterFX 5.0 so I could easily control the cross fades. I laid out the shark's spine and ribs in AutoCAD. Once the dimensions were set, they were handed back to Dave for finishing while I started bending metal.

The shark's skeletal frame consists of a Makrolon polycarbonate spine and stainless steel ribs. For the spine, we needed a material that achieved close to natural buoyancy in salt water, and was strong, light, flexible, and cost-effective. Ultimately, we stacked individual polycarbonate sheets together to form a 0.075-inch-thick laminate.

Since the ribs were to provide the skeletal shape, lend buoyancy to the design, and function as a kind of swimming roll cage, they had to be both strong and light. We chose to make them out of stainless steel tubing of varying diameters and lengths, plugging the ends with PV and sealing them with a rigid spray foam-and-silicone concoction. Overall, the rib cage consists of 30 full or 60 rib-halves, bent into a semicircle of approximately 180 degrees. The ribs closest to the head have a 2-inch diameter and a 0.065-inch wall thickness, with descending ribs decreasing down to a 1-inch diameter. This design allows rigidity in the vertical direction and flexibility in the horizontal direction (the body can flex almost 170 degrees).

We constructed the shark head out of of 0.0625-inch-thick fiberglass, hand-laying it up over a brushable urethane elastomer (which we also used to create the skin). Our artist then air-brushed the head, using photos of real sharks for a guide. She sculpted gums from epoxy and molded hundreds of plastic serrated teeth. Our company tooth fairy, Georgie, even cut a few of them to duplicate broken teeth.


Powered by Air: Eddie Paul's shark is basically powered by compressed horsepower on tap -- a scuba tank with 140 ft3 of air pressurized to 3,000 psi. A standard scuba regulator connects to the main supply and drops the pressure from 3,000 to 200 psi. When pressure is directed to the rear of the left or right piston, it will extend. When applied to the front, it will retract. The alternating motion of the pistons pulls on the cables connected to the tail causing the shark to swim.

One Giant Toy, Powered by Air

Next challenge: How could we power this bag of pipe and plastic? We chose pneumatics because we're familiar with the technology, and it can be used directly in saltwater without costly waterproof housings. It also can be recharged at sea by simply changing the scuba bottle.

We were able to reduce the pressure to 200 psi by employing the first stage of a two-stage scuba regulator. This lower-pressure air can then be connected to a four-way control valve, which redirects it (via a simple joystick) to opposite ends of two air cylinders. The pair is mounted to ribs near the front of the shark near the gill area and connected to the tail by a stainless-steel aircraft cable.

As the cylinder on one side of the shark is extended, the opposite cylinder is retracted. This transfers the linear motion of the two cylinders into a lateral movement of the tail by "bowing" the flexible spine from side to side, mimicking the oscillating motion of a shark's tail as it swims. As the control stick is moved in the opposite direction, the two cylinders reverse, driving the tail in the opposite direction.

During the test phase we found that a short (6-inch stroke), side- to-side motion created an underwater vortex almost 12-inches deep at the termination of each tail stroke. The stroke length of the cylinder determines the stroke of the tail, while the power of the stroke is a result of the diameter of the cylinder and the pressure applied in the cylinder. After testing different bore diameters and stroke lengths, we standardized on a 1.5-inch bore and 12-inch stroke.

The shark can be turned by the same control stick and a technique of timed movements of the stick. For example, pushing the stick to the left for two seconds moves the tail left one full stroke. Pushing the control stick to the right for one second moves the tail right about half the distance. Repeating this motion will allow the tail to act as a power device and a rudder, turning the shark in the direction that the control stick and tail is held in the longest. To aid navigation, we mounted a video camera in a rubber remora on the shark's body-making it the world's first "remoracam."

After the air is expelled from the cylinder, it travels back to the control valve and is redirected to two empty, carbon-fiber-wrapped air tanks. They function as storage tanks for the spent air and will allow for short runs in a "stealth non-bubble" run. The tanks then can be vented to the sea, or the main pressure (scuba) tank can be disconnected from the control valve and the system run in reverse. The pilot also has the option of simply dumping the storage tanks and not reusing the air.

None of this, of course, had ever been accomplished by anyone before. But even while navigating the depths of the unknown, we completed the project on schedule and within budget!

Reach inventor Eddie Paul at [email protected]

Resources
Makrolon Polycarbonate
from Sheffield Plastics:
http://rbi.ims.ca/3850-556
PRISM closed circuit diving systems
from Steam Machines:
http://rbi.ims.ca/3850-557
Directional control valves
from ARO:
http://rbi.ims.ca/3850-558
Pneumatic cylinders
from Parker
http://rbi.ims.ca/3850-559
TAGS: Materials
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