Think commuter traffic crawls along slower than a snail? As this ScienCentral News video reports, one day you might be able to ride straight up or down or over whatever’s in your way, thanks to what engineers are learning about that snail's pace.
Slow Pokes
When you're stuck in traffic, a snail literally might be able to beat you to your destination. Snails may be slow, but in motion, they are very versatile: they can climb up or over anything—and even do so upside down.
Snails are a type of mollusk, with a soft body—made up of a head and a single flat foot—protected by a spiral shell. They can be tinier than a fraction of an inch, or as long as almost two feet. Now these mechanically simple yet mobile invertebrates have their first robotic counterpart, dubbed RoboSnail, a six-inch robot that mimics the way real snails move. "Snails can climb up trees, over rocks, up vertical walls, across ceilings," says Anette Hosoi, professor of mechanical engineering at Massachusetts Institute of Technology who created RoboSnail with graduate student Brian Chan. "So the idea is, can we mimic this sort of motion that snails have, to build something that can actually climb over all kinds of complex terrain?"
Real snails travel on their single foot along a trail of mucus, a slimy fluid secreted by a special gland in the foot. Snails move by pushing the mucus between their foot and the ground or other surface. Snail mucus is an example of a non-Newtonian fluid, a type of fluid of particular interest at MIT’s Hatsopoulos Microfluidics Laboratory, where Hosoi and Chan work. Unlike Newtonian fluids such as oil or water, non-Newtonian fluids change their properties and thicken when they're subjected to stress, such as downward pressure from a snail's foot. Since snails use different mechanisms to move, Hosoi and Chan designed two RoboSnails, each mimicking a different method of snail locomotion.
RoboSnail image: Anette Hosoi, MIT
The team's first RoboSnail imitates a snail mechanism that Hosoi compares to the up-and-down motion of ocean waves. "There's a wave that propagates along the bottom of the snail’s foot," explains Hosoi. "And the wave can either propagate in the direction that the snail is moving, or it can propagate backwards." The first RoboSnail's version of mucus is silicon oil combined with clay particles. Its body is a series of plastic plates strung along a wire helix that is connected to a small motor Chan borrowed from a toy car. When the motor is running, the plates create a wave in a rubber foot.
A second RoboSnail mimics another snail motion, one that works like a bump moving along the length of a rug. "When you have a bump in a carpet," Hosoi explains, "and you start to push on it, the majority of the carpet stays stationary. But you can push on the bump and move it to the far end of the carpet, until the carpet lies flat again."
Hosoi's interest in snail motion grew out of her studies of how fluids move at very small scales, including the way blood moves through veins. She began by asking, "If we have a system where we have a fluid that is bounded by an elastic membrane, such as a blood vessel, what sorts of characteristics does that system exhibit? Under what conditions will the system collapse? One of the systems we were looking at was a flat elastic membrane with a fluid flowing underneath it." Hosoi asked Brian Chan if he could build an apparatus to test an elastic membrane-and-fluid system. Chan had already built a mechanical version of a water strider, an insect that can skim over the surface of ponds. That project had offered Chan plenty of opportunities to observe snails. So he told Hosoi that the system she wanted to test is "exactly how snails move."
Now that two RoboSnails exist, what could they do? Hosoi foresees that: "you could build small snail feet, and you could attach them to the bottom of something heavy like packing crates. With a remote control, you can have your crates crawl where you need them to go." In fact, another researcher in the Hatsopoulos Lab, Todd Thorsen is at work building a smaller RoboSnail. Hosoi also has been approached by companies interested in enlisting RoboSnail's help in exploring for oil deep in the earth, where heat and pressure are enormous.
Although Hosoi admits that Robo Snail has traveled far from its origins in her studies of blood flow, it might contribute to the development of tiny pumps and valves for a future "lab on a chip," through which blood could be passed for analysis. Meanwhile, Hosoi and Chan are working on what they consider the ultimate goal of robotic snail research: "To build some kind of an apparatus that will crawl across the floor and then go straight up a vertical wall," says Hosoi.
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