Duke Robot Named Most Innovative in Recent Underwater Competition

A translucent, blue flying-saucer-shaped underwater robot created by Duke students whirled and skimmed its way to a prize for the most innovative design at a recent competition.

Dubbed Charybdis -- after a mythical Greek sea monster that gulped and spewed seawater to create deadly whirlpools -- the robot won the $1,000 prize for innovation in the international 2004 Autonomous Underwater Vehicle Competition. The competition, sponsored by the Association for Underwater Vehicles Systems International and the Office of Naval Research, was held July 28-Aug. 1 in San Diego. The Duke team from the Pratt School of Engineering and the Department of Computer Science finished fifth overall; an MIT team took first place.

"We appreciate the prize for innovation because we went for a completely new design on the cutting edge of electronic control," said Tyler Helble, Duke team captain and lead electronic engineer on the autonomous underwater vehicle (AUV) project. "The only thing old about Charybdis is its name."

With a diameter of only 28 inches and weight of 90 pounds, Charybdis is propelled laterally by three reversible horizontal thrusters spaced around its thin outer edges and vertically by a reversible propeller mounted through its center. Charybdis bristles with sensors, including downward- and forward-facing video cameras, an altimeter to measure distance above the bottom, a pressure gauge to measure depth, four sonar sensors to determine velocity, hydrophones to detect the direction of sounds, a compass for directional bearing, and a gyroscope to help determine pitch and roll.

A compact onboard computer, roughly equivalent to an old home PC, processes information from all the sensors. "The computer determines where Charybdis is relative to where it started and identifies targets," said Ethan Eade, the lead software engineer. "It calculates how much force each thruster should use in which direction to move Charybdis to a target."

The Duke team chose the flying-saucer shape over the usual cigar-like submarine design to improve control. "The submarine shape is faster in a straight line, but the saucer shape moves well in any direction," Eade said.

"Charybdis can move in any direction at any time without having to turn," said adjunct professor Jason Janet, project adviser. "It can aim its sensors where it wants no matter which direction it is moving, a big advantage homing in on a target."

The contest allowed each robot 15 minutes to complete three tasks. The first was finding and passing through an underwater gate. The second task placed a premium on visual sensing and precise maneuvering. A light identified the position of target bins valued at 300 to 500 points each. The robots had to find the light, home in on bins and drop in markers. The third task rewarded excellence in acoustic sensing. An acoustic "pinger" pulsed from the center of a recovery zone surrounded by a floating line. The goal was to find the zone and surface inside the line.

Practice sessions and preliminary competition were arduous, said Johnston, an electrical and mechanical engineering major. "We spent days at the pool and nights getting ready for the next day."

Eade had to rewrite software for the Navy test pool, an ellipse as long as a football field, different in size, shape, lighting and sonar characteristics from Charbydis' home at the Wilson Recreational Center diving pool.

A failed center thruster forced the team to temporarily move an outer thruster into the center channel. Eade changed the propulsion software until a replacement part arrived. When some acoustic systems malfunctioned, Eade adjusted the software to rely more on video.

Charybdis provided a few welcome moments of comic relief. "When we changed the navigation to use video more, Tyler was in the pool holding a target bin and Charybdis tracked him like a predator," said Johnston. "Tyler couldn't get away."

A typo almost transformed Charybdis into a real flying saucer. "We sent Charybdis to a depth of plus one meter instead of minus one, and it sat on the surface with the center thruster blowing a hole in the water, trying to lift off," Eade said.

Josh Johnston said MIT and Duke had the only two robots during the final weekend to drop a marker in the 500-point bin and surface in the recovery zone. "We were the most consistent in practice," Johnston said.

Unfortunately for the Duke team, the consistency did not last through the finals. "Charybdis executed a beautiful search pattern but both video cameras failed and so it never saw the bins," said Johnston. "It still dropped a marker less than a foot from the 500-point bin and surfaced within four feet of the recovery zone."

Charybdis helped launch a career for Helble '04, an electrical engineering and environmental science major from Okemos, Mich. He will work on AUVs for the Navy's Space and Naval Warfare Systems Command, the competition's host. Eade '04, computer science and mathematics, Timonium, Md., will study information science at Cambridge on a Marshall Scholarship.

Other team members attending the competition were Pratt students Peter (Andy) Smith '05, Raleigh; Julien Finlay '06, Smithfield, R.I.; Jamaal Brown '05, Gary, Ind.; John Felkins '05, Berwyn, Penn.; and Shawn Haigh '04, Canton, Mass.

The Duke team received support from the Lord Foundation, SAIC, Deep Ocean Engineering, DigiMarc, Subconn, American Standard, RD Instruments, Tritech International, Global Water Instrumentation and the Duke Engineering Alumni Council.