Tiny Micro robots and their power

(Part-1) collected from youth wave.

This is one in a series presenting news on invention and innovation, made possible with generous support from the lemelson foundation.

A group of ants can move objects many times larger and heavier than themselves. This ability inspired a team of researchers to develop small robots that can do the same
thing. The team created 29-millimeter (1.1 inch) long robots that can get a firm grip on the ground. In tests, six of the ‘bots have just worked together to tow a full-size car.

They didn’t move the car quickly. To haul it 12.5 centimeters (5 inch) took about one minute.

When ants carry a large item, such as a piece of food, they need good traction. To get a better grip, each ant presses its feet down harder. This increases the area of contact between each foot and the surface. Such ants served as the inspiration for david christensen and his team of mechanical engineers  at standford  university in palo alto calif. (mechanical engineers use physics and materials science to design tools and machines.)

Ants can cling to a smooth wall or surface using small pads on their feet. When an ant puts its foot down, a tiny deoplet of sticky gel oozes between the pad and wall. This holds the ant in place. When walking, only tiny bits of the ants feet stick to the ground. That makes it easy for the ant to move quickly. The mechanical engineers wanted to create miniscule robots capable of moving big, heavy objects. But robots can’t ooze liquid the way ants do. Using sticky gel wasn’t an option for the tiny ‘bots. So the researchers turned their attention to gecko feet.

Making sure-footed micro robots

The bottom of a gecko’s  foot has layers of tissue covered with tiny hairs. When the critter puts weight on the foot, those structures spread out. This increases between the foot and the surface to which the gecko clings. That contact allows van der waals forces to hold the foot onto the surface. Van der waals forces are tiny electrical attractions between molecules. By increasing the surface area between its foot and leaf, wall or other object, the gecko uses enough van der waals force to stay in place. Such stickiness is called adhesion.

Adhesion is one step, christensen points out. But just as important is the ability to release the connection. Otherwise, he explains, “an insect or robot would become stuck and could not move.” So the team designed its robot based on the need to both stick and easily release its “foot.”

To do this, they created a 25-millimeter by 25-millimeter (1-inch by1-inch) foot for their 29-millimeter long robot. They covered the underside of that foot with tiny wedges of a rubber like  substance made of silicone. Each wedge was just 0.1-millimeter (0.004-inch) long. When the robot rested on the ground, only the tips of a foot’s wedges touched down. But when a foot moved forward, the wedges laid down flat, increasing contact with the floor. Like the gecko’s foot, this triggered an increase in the van der waals force, anchoring the foot in place.

Flattening the wedges also added spring energy to them. Think of a spring the has been pressed together. When released, the coils burst apart. The same kind of energy in the wedge allowed them to spring loose when they were released. The team ended up with a tiny robot that they called ?tug. (in science, the greek letter?, Or mu, means “micro”.) the ?tug has a single foot and tow wheels for traveling, plus a winch that could reel in a heavy object, known as a payload, which is connected by a string.

The ?tug moves forward on its wheels then squats down, anchoring to the ground with its foot. Now it uses the winch to haul the payload closer. The foot then releases and the string unwinds as the ‘bot wheels forward. Then it stops and repeats the anchoring, winching and release.

By this means, the 12-gram (0.26-ounce) ?tug was able to pull a 22.5-kilogram (50-pound) payload. That means the micro robot nearly 2,000 time its own weight!

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