Underwater vehicles have become good at using propellers and thrusters to stay in one place, even in strong currents. But holding on to a surface while exerting force to do a job has been a challenge. Now, MIT researchers are tackling this issue by designing a “controllable adhesion system” that offers various advantages for underwater robots, including a high holding force on various geometries and textures, low energy consumption, chemical resistance to seawater, and low maintenance requirements.
The researchers are working on several approaches, but their best success to date has come using “controllable electromagnets” — magnetic devices that can easily be turned on and off using little energy. The group designed a module consisting of two parallel bar magnets next to each other. One is a very strong magnet made of neodymium, iron, and boron (NIB). The other is a weak magnet made of aluminum, nickel, and cobalt (alnico). Around the alnico magnet is a coil through which an electrical current can flow.
After conducting experiments and simulations, the researchers refined the design to improve its performance. In the new design, the two magnets are concentric rather than parallel bars. At the center is a cylinder-shaped alnico magnet, and surrounding it is an NIB magnet shaped like a hollow tube. A coil around the outside can carry current to switch the polarity of the alnico magnet. (The NIB magnet is too strong to be affected.) In this configuration, the module can still be switched on and off. But now the whole structure can be covered by a steel cup — an outside shell that confines the magnetic field to the open side and minimizes its leakage when the module is clamped on to a surface.
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Also: Learn more about the capabilities of autonomous underwater vehicles (AUVs).
