An underwater robot the size of a football could provide quick, effective security against ships attempting to smuggle people and goods past border security. The craft is designed to skim just outside the hull of ships, examining the vehicles for any hidden compartments where contraband could be hidden.
Ultrasound is used to examine through the outer hull, revealing changes in material density and composition that could give away the presence of smuggled material. Like a slightly deflated football sitting on a table, the new device has one flat side that can run along the hull during an examination.
A unique propulsion method allows the small automated vehicles to roam just under the surface of the water without being detected. This would allow clusters of the underwater surveillance devices to operate near ports, hiding in small patches of grass or algae. Ships approaching the port would be searched using fleets of the inexpensive drones.
"It's very expensive for port security to use traditional robots for every small boat coming into the port. If this is cheap enough -- if I can get this out for $600, say -- why not just have 20 of them doing collaborative inspection? And if it breaks, it's not a big deal. It's very easy to make," said Sampriti Bhattacharyya, a graduate student in mechanical engineering at the Massachusetts Institute of Technology (MIT). She designed the robot in collaboration with her faculty adviser Harry Asada.
The flat side of the aquatic drone is waterproof, while the rounded sides are water-permeable. Within the device is a motor consisting of six pumps that push water through rubber tubes, providing propulsion. Two of which press the marine drone against the hull being inspected, while a pair at each end delivers thrust. The exhausts are each placed at specific angles in order to provide the greatest degree of maneuverability.
"It's very similar to fighter jets, which are made unstable so that you can maneuver them easily. If I turn on the two jets [at one end], it won't go straight. It will just turn," Bhattacharyya stated.
Three accelerometers and a trio of gyroscopes are used to constantly recognize the position and movement of the robot. An on-board processor then directs propulsion through the jets to control the automated device.
Major components of the new drone were manufactured using a 3D printer, an aspect to the design that could radically lower production costs.
One old challenge of the sea faces Bhattacharyya and the new surveillance robots: barnacles. Ultrasound devices require the sensing device to either be in contact with the surface being examined, such as the belly of a pregnant woman, or be separated by a specific distance, determined by the frequency being examined. Water could be used to create hydrodynamic buffers, overcoming this problem.
The new marine drones operate about 40 minutes on a single charge.
