The device doesn’t look like
much: a caterpillar-sized assembly of metal rings and strips resembling
something you might find buried in a home-workshop drawer. But the technology
behind it, and the long-range possibilities it represents, are quite remarkable.
The little device is called a milli-motein — a name melding its
millimeter-sized components and a motorized design inspired by proteins, which
naturally fold themselves into incredibly complex shapes. This minuscule robot
may be a harbinger of future devices that could fold themselves up into almost
any shape imaginable. To build the world’s smallest chain robot, the team from MIT’s
Center for Bits and Atoms, had to invent an entirely new kind of motor: not
only small and strong, but also able to hold its position firmly even with
power switched off. The researchers met these needs with a new system called an
electropermanent motor.
The motor is similar in principle
to the giant electromagnets used in scrapyards to lift cars, in which a
powerful permanent magnet is paired with a weaker magnet (one whose magnetic
field direction can be flipped by an electric current in a coil). The two
magnets are designed so that their fields either add or cancel, depending on
which way the switchable field points. Thus, the force of the powerful magnet
can be turned off at will — such as to release a suspended car — without having
to power an enormous electromagnet the whole time. In this new miniature
version, a series of permanent magnets paired with electromagnets are arranged
in a circle; they drive a steel ring that’s situated around them. The key
innovation, is that they do not take power in either the ‘on’ or the ‘off’
state, but only use power in the changing state, using minimal energy overall.
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