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A Mechatronic Submersible: the Super Falcon

By Lawrence D. Maloney, Contributing editor
Looking for adventure? How about a frolic in your own personal submarine hundreds of feet below the surface of the ocean?

If you've got the cash - by some reports about a million dollars - Hawkes Ocean Technologies (HOT) can put you in the driver's seat. The San Francisco area company, which has designed and built the majority of the world's manned submersibles since the 1970s, is getting ready to debut its most advanced vessel yet, the Super Falcon, in the Spring of 2008.

Blending a sleek winged design with advanced mechatronics' concepts, the craft promises to meet company founder Graham Hawkes' goal of pushing the envelope in "deep water flight."

Tracing the Pedigree

The Super Falcon follows a 30-year history of designing and building subs. Originally, Hawkes focused on Atmospheric Diving Systems, such as the Wasp and Mantis, for the offshore oil and gas industry. Then he moved to conventional submersibles he called Deep Rovers. In the late 1980s, Hawkes and his team shifted to winged designs, which embodied a new generation of lightweight micro-submersibles that require no ballast and operate on the same principles as flight through air.

"Super Falcon is the third generation vehicle in our line of Deep Flight winged submersibles," says Hawkes. "The wings came about originally because of our interest in building a full ocean-depth vehicle as an alternative to a massively heavy conventional submersible. When we launched our first winged sub, Deep Flight I, and saw the public interest in underwater flight, we realized we wanted to pursue underwater flight for its own sake, regardless of depth."

As Hawkes tells it, Super Falcon is "leaps ahead" of the company's prototype flier, Deep Flight Aviator. "When you are trying to push the frontiers of design, you either focus on the concept; keeping the technology conventional, which is what we did with Deep Flight Aviator, or you can push the technology," Hawkes says.

Geometry Shapes Performance

The Super Falcon will weigh about 4,200 lb and is designed as a two-person performance submersible. Like HOT's previous submersibles, it is always positively buoyant and has no variable ballast system. Instead, the craft relies on hydrodynamic forces on its wings to fly beneath the waves. This provides an inherent safety feature, says Mechanical Engineer Adam Wright. If the sub were to ever lose power or get into trouble, it would float back to the surface.

Only the pilot and co-pilot and a small amount of life support and control hardware are encapsulated in the main pressure hull. All other components, such as thrusters, actuators and batteries, are either designed to operate under pressure or are housed independently. This minimizes the volume of the pressure hull, which in turn reduces the total surface area subject to hydrostatic pressure and keeps weight down.

For increased performance, the team designed the shape of the pressure hull to minimize frontal area, while still maintaining passenger comfort. As such, the geometry of the pressure hull is inefficient at withstanding ocean pressure compared to conventional geometrical shapes such as spheres or cylinders. To compensate, the pressure hull will be constructed of very strong carbon fiber/fiberglass composites and will maintain a safety factor of three with an operational depth of 400 to 1,500 ft.

For propulsion, the sub relies on a large diameter dc brushed motor powered by pressure-compensated lithium polymer batteries. A single electric thruster can generate up to 500 lb of thrust. The sub will cruise at an estimated maximum horizontal velocity of 7 knots, with a much greater vertical ascent velocity. An independent ball screw linear actuator will control each axis of flight control (pitch, roll and yaw).

"The sub will fly by wire, in that the flight controls are driven by electrical signals instead of mechanically, which would have required reciprocating seals in the pressure hull," says Wright.

Because the sub is designed purely to explore underwater flight, it will not have a "hover" mode and will always need to maintain some speed to stay submerged. As a result, it will not carry any manipulator, although future research-based submersibles will have manipulators and be capable of hovering.

Safety in the Deep

In designing the sub's electrical and control systems, the major concerns were safety, reliability, flexibility and accessibility, according to lead Electronics Engineer David Jeffrey. "Because we're working around seawater and because there will be crew and divers in the water during submarine operations, it is dangerous to have high voltages," he says. "Our submarine runs on a 50.4V battery power system, heavily monitored during maintenance and operation. This is a good compromise between excessive voltages and having to handle very high currents."

Jeffrey adds, the best design electronics approach is to "minimize the things that experience tells us tend to go wrong." In submarines, this mainly involves areas where electronics and seawater can come together, such as underwater connectors and sealed one-atmosphere housings, particularly if they have a moving seal. Static seals perform far better, says Jeffrey, as do brushless dc motors, which can run in an oil-filled housing at ambient pressure.

Since the team wanted to limit the number of wires passed between the exterior and interior of the sub, the engineers realized a networked control system, based on standard modules, would work best. That solution also addresses accessibility issues. The sub has a "diagnostic port," which permits a PC to communicate with all of the nodes. Everything sub pilots might want to adjust is stored in EEPROM in the nodes and can be read and changed as needed. Using a bootload program, one can even upload a whole new suite of software to the nodes.

Another huge advantage of a network, according to Jeffrey, is that it can be extended. Adding a node does not require adding wires. This is a great improvement over the old, hard-wired systems, which used preset potentiometers for all adjustments and separate wires for every function.

Essential Design Tools

To bring all these design innovations to life, the HOT team turned to a full suite of software tools. For mechanical work, the engineers relied heavily on Autodesk Inventor Professional 11. "The software allowed us to model a design rapidly to a conceptual stage that could be viewed in 3D by all members of the team," says Mechanical Engineer Wright. "This allowed everyone to pitch in their ideas."

Also very valuable, adds Wright, were ANSYS Mechanical (FEA stress analysis simulation software) and ANSYS CFX (computational fluid dynamics software). "Because the shape of the pressure hull is so unconventional and organic, one cannot easily calculate its internal stresses or interaction with other components," he says. "But with ANSYS Mechanical, we can iterate different designs and get visual results within minutes."

For the electronics design, Jeffrey did most of his general drawing with Zoner Draw 5, a low-cost package he has used for many years. He also does PCB design with BoardMaker3 and for AVR microcontroller software, he uses Atmel's AVR Studio and CodeVisionAVR compiler. AVR Studio supports two different methods of de-bugging. "You can run your code in an emulator on a PC or you can use a JTAG interface to permit debugging in the target hardware," says Jeffrey.

The team developed most of its PC software for the sub using Just BASIC and Visual Basic. They also turned to Just BASIC to develop network diagnostic and monitoring programs. Terminal v1.9b by Bray was an important serial port diagnostic tool. Among other useful tools cited by Jeffrey: PSPad for program editing, WizFlow for generating flow charts, MultiSim for simulating board hardware performance and MathCAD for modeling stepper motor controls.

In addition, Electronics Engineer Charles Chiau relied on Autodesk Maya 8.5 for underwater lighting simulations. By importing the model from Autodesk Inventor and placing a simple camera in the cockpit simulating the pilot's perspectives, engineers were able to create artificial underwater environments and test various configurations of the lights on the Super Falcon. "This software was a great tool for giving us a feel for what the sub's pilots would see," says Chiau.

Hawkes points out that this rich lineup of computer tools enabled HOT to reduce the Super Falcon design team to the bare minimum, four or five engineers. "Once you get down to that number, the communications issues that plague bigger teams just don't exist," he says.

Chiau also cites the importance of weekly brainstorming sessions involving a team from a variety of engineering backgrounds. "It is extremely important that we collaborate because our subs are a fusion of electrical and mechanical components," he says.

Chasing the Market

Tom Perkins, founder of the venture capital firm Kleiner Perkins, will be the first owner of a Super Falcon. The sub will be operated from his sailing yacht, The Maltese Falcon. "Tom is truly pioneering underwater flight with us," says Hawkes.

And the cost? "If you have to ask how much, then you cannot afford them!" adds Hawkes. "But we hope to eventually get our costs down to the range of the light aviation industry. We're always looking at ways to reduce costs, including licensing the technology to a qualified manufacturer."

The HOT team is already working on what Hawkes describes as an "extreme submersible with extraordinary performance capability beyond anything that exists." This project may be announced before the end of 2008.

As Hawkes explains it, about two thirds of our planet is covered by water, yet there are only five deep submersibles in the entire world. To give customers more choi