AsianScientist (Feb. 25, 2016) – A researcher based in Japan has designed a paddle boat driven by magnetic gears.
In a study published in Physical Review Applied, postdoctoral scholar at the Okinawa Institute of Science and Technology Graduate University (OIST), Dr. Johannes Schönke, presented his theory of the possibilities and applications of smooth magnetic couplings, which can produce an even motion without any counterforce.
Magnetic gears transmit rotary motion like mechanical gears, but instead of teeth, they use magnetic attraction and repulsion between rotating magnets. Magnetic gears have several advantages over mechanical gears. They are contactless, an advantage over the mechanical gears found in say, a watch, which transmit motion through contact between moving teeth.
Furthermore, they require less maintenance, no lubrication, are more reliable and efficient, and produce lower vibration and noise. Magnetic gears are often based on an alloy of iron, boron and neodymium, which creates the strongest permanent magnets to date.
Food mixers in the kitchen, magnetic stirrers in a chemistry lab or other industrial magnetic couplings are based on the idea that the two magnets rotate around the same axis.
“I wanted to explore the possibility of positioning the input and output axes at any desired inclination angle,” explained Schönke.
“Furthermore, there are certain configurations of the two magnets that allow the addition of a third magnet at a specific position and still maintain a smooth coupling.”
To illustrate, Schönke modeled a paddle boat where two magnets are connected to the paddles and one to the driving system. If the magnet of the driving system is rotated, the paddles move in a synchronized way to push the boat forward.
Interestingly, because of the contactless nature of the magnetic coupling, the paddle axle does not need to penetrate the hull and can be fixed outside of the boat. However, the specific triangle geometry between the positions of the three magnets is crucial, to make the coupling work smoothly.
As for the paddles, the motion of mini pumps and valves inside micro-channels can also be controlled without the need for contact.
The same analogy between mechanical and magnetic gears can be further explored by considering the interaction between a quadrupole and a magnet, each rotating around a specific axis. One way to construct a quadrupole is to place four magnets like a cross, positioned in a way that two north poles and two south poles alternatively face the center.
The quadrupole can be thought of as a gear with twice as many teeth as the single magnet. When the magnet is rotated by a full cycle, the quadrupole rotates only half a cycle. By rotating the magnet, the quadrupole rotates correspondingly, as it would happen with a mechanical gear wheel mechanism.
In future, this type of technology will be particularly useful for micro- and nanosystems.
“The next step is to build a 3D printed toy-size car based on the design principle of the paddle boat using three strong inch-sized spherical magnets,” said Schönke.
The article can be found at: Schönke (2015) Smooth Teeth: Why Multipoles are Perfect Gears.
Source: Okinawa Institute of Science and Technology Graduate University.
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