In pursuing advances in cooperative robotic control and communication, Daniel Stilwell is developing a platoon of autonomous underwater vehicles (AUVs) that will both study the ecological effects of man-made nutrients on Virginias coastal waters and help develop search, survey, and tracking methods for the U.S. Navy.
|A fleet of Virginia Tech AUVs will be used to help the Navy develop underwater search and tracking capabilities and will help marine scientists determine the health of coastal ecosystems. (Click photo for larger image)
He has recently won two prestigious young faculty awards to support these efforts: a $400,000, five-year NSF Career Award and a $300,000, three-year Young Investigator Award from the Office of Naval Research (ONR). Both honors are the top awards given to young faculty by those agencies. ONR gives only 26 Young Investigator Awards each year.
Developing Robots Real-World Skills
Stilwells goals are to develop control laws so that autonomous vehicles can solve problems cooperatively. Many researchers have been working to develop cooperating autonomous robots, he said, but there is often a gap between theory and practice. We are developing theories of robot cooperation, and we require that our results work in the real world, and not just the laboratory, he explained.
Stilwells real-world environment will include the coastal waters of Hog Island Bay on Virginias Eastern Shore and the York River where it meets the Chesapeake Bay. For the NSF Hog Island Bay experiments, the AUV platoon will track and measure dissolved oxygen over a large area of the bay and along a moving tidal front over a one to two-hour period. The platoon will also detect and map any freshwater seepage at the bottom of the bay.
The dissolved oxygen measurements will be used by marine scientists to estimate metabolism of the bay and to determine the overall health of the estuary system. Ultimately, scientists hope that the data will enable them to determine fate of nitrogen from agricultural and urban runoff. Understanding exactly how nitrogen is buffered in a coastal estuary is critical for understanding the role of man-made pollution in the oceans and coastal watersheds, Stilwell said.
In the ONR York River project, the AUV platoon will be used to develop mapping and tracking methods in four dimensions (space and time) for the development of underwater sensor networks, mine countermeasures, and wide-area search and survey tools. The energetic environment of the tidally-driven York River presents a challenging unstructured environment in which to address communication, navigation, and cooperation issues.
The experiments are highly complementary, Stilwell said. The Hog Island Bay project seeks to determine best practices for controlling the coordinated motion of cooperating AUVs once it has been determined where they should go. The York River project seeks to determine where they should go.
The VT Miniature AUV
Stilwells projects rely on a fleet of low-cost miniature AUVs that his team is building. The Virginia Tech AUVs are the smallest known fully functional underwater vehicles to be developed to date, yet the cost for components is less than $2,000. They navigate using a custom-engineered miniature inertial system, miniature single-beam altimeter, and single-beam forward-looking sonar. When surfaced, they utilize GPS for precise positioning and communicate via a radio modem.
|Daniel Stilwell assembles the Virginia Tech Miniature Autonomous Underwater Vehicle (AUV). At 70 cm long and 8.9 cm wide, it has an expected cruising speed of 2-3 knots and expected range of 30 km. Its payload capability includes navigation sensors and environmental sensors.
Due to its low cost and high functionality, the Virginia Tech miniature AUV is an ideal platform for multi-vehicle underwater research, Stilwell said. Although other AUVs could be used for multi-vehicle research, their costs and infrastructure requirements are prohibitive.
Control & Communications Challenges
Building the AUV platoon is Stilwells first challenge. We also need to resolve issues of group interaction and communication, he said. In getting autonomous vehicles to solve problems cooperatively, a key issue is communications, he explained. Our fundamental question is how, what, and when should robots communicate to cooperatively solve a problem? A major task for us will be to minimize communication requirements between vehicles. Our AUVs will only be able to communicate when they periodically surface.
Stilwells team also needs to determine the best navigation and controls approach. Getting all these vehicles to navigate in an unstructured environment will be a challenge, he said. Seeing an obstacle and navigating around it is low-level behavior, but how does a vehicle cope with an event or obstacle that it was not programmed for? How does the whole platoon move forward with its task while individuals cope with their own needs, such as obstacle avoidance?
The challenges faced in these projects also apply to robotic platoons on land and in the air. Underwater is an ideal testbed, he said, but through these experiments, we hope to develop theoretically justified distributed control laws that enable autonomous robots to cooperate anywhere.
Extending Underwater Robotics
To Middle & High Schoolers
The oceans depths can be more accessible than space and Stilwell believes underwater robotics will spark the imagination and daring of todays youth. He hopes to capitalize on the publics interest in underwater technology in both educating engineers and encouraging others to consider the field.
He plans to develop undergraduate and graduate courses in underwater robotics, and extend access to the technology to students in middle school and high school.
The materials developed for the university-level courses will be used as a basis for an Autonomous Underwater Vehicle Competition for students in high school and middle school. AUVs are fun, he said. Although the technology is difficult, we believe we can package it so that teenagers can get a taste of engineering in a cost-effective way.
The Association of Unmanned Vehicle Systems International (AUVSI) sponsors a popular underwater robotics competition at the university level. The AUVSI competition is an outstanding experience for the undergraduate and graduate student participants, he said, but it is technically ambitious and very challenging. No one has ever completed the program goals and it takes a team several years of experience to develop an AUV that is remotely competitive.
He is working with Jim Bales of MIT to develop an adjunct to the existing contest that is technically less sophisticated and more accessible to younger students. Student teams will be presented with a project goal, a box of parts, and educational materials. We will also seek sponsorship from industry and professional societies to provide mentors, exposing students to practicing engineers and increasing the likelihood that they will pursue engineering or science fields in the future.