Allison Carter, Georgia Tech

SlothBot’s Slow and Deliberate Pace Saves Energy

June 7, 2019
Being slow can be a definite advantage in many applications, including environmental monitoring and security.

A robotic monitor that is slow and an energy miser can be far superior to one that is fast and an energy guzzler for many applications, including environmental monitoring, precision agriculture, infrastructure maintenance, and a slew of security applications. That’s where “SlothBot,” the brainchild of researchers at the Georgia Institute of Technology, comes in handy. It is powered by two photovoltaic panels and designed to linger in the forest canopy for months measuring environmental changes and move only when it must.

“In robotics, it seems some are always pushing for faster, more agile, and more extreme robots,” says Magnus Egerstedt, an engineering professor and principal investigator for SlothBot. “But there are many applications where there is no need to be fast. You just have to be out there persistently over long periods of time, observing what’s going on.”

Based on what Egerstedt called the “theory of slowness,” grad students Gennaro Notomista and Yousel Emam built SlothBot using 3D-printed parts for the gearing and wire-switching mechanisms needed to crawl through a network of wires in the trees.

The gears and switches that let the robot switch from one cable to another were made using 3D printing.(Photo: Allison Carter)

The greatest challenge for a wire-crawling robot is switching from one cable to another without falling, says Notomista: “The challenge is smoothly holding onto one wire while grabbing another. It’s a tricky maneuver and you have to do it right to provide a fail-safe transition. Making sure the switches work well over long periods of time is really the biggest challenge.”

Mechanically, SlothBot consists of two bodies connected by an actuated hinge. Each body houses a driving motor connected to a rim on which a tire is mounted. The use of wheels for locomotion is simple, energy-efficient, and safer than other types of wire-based locomotion, the researchers say.

SlothBot has so far operated in a network of cables on the Georgia Tech campus. A new 3D-printed shell  that makes the robot look more like its namesake, a sloth, protects the motors, gears, actuators, cameras, computer, and other components from the rain and wind. That will set the stage for longer-term studies in the tree canopy at the Atlanta Botanical Garden, where Egerstedt hopes visitors will see it monitoring conditions as early as this fall.

The name SlothBot is not a coincidence. Real-life sloths are small mammals that live in the jungle canopies of South and Central America. Making their living by eating tree leaves, the animals can survive on the daily caloric equivalent of a small potato. With their slow metabolism, sloths rest as much 22 hours a day and seldom descend from the trees where they can spend their entire lives.

“The life of a sloth is pretty slow-moving and there’s not a lot of excitement on a day-to-day level,” says Jonathan Pauli, a zoology professor at the University of Wisconsin-Madison, who has consulted with the Georgia Tech team on the project. “The nice thing about a slow life is that you don’t need a lot of energy.”

That’s exactly what the researchers expect from SlothBot, whose development has been funded by the U.S. Office of Naval Research.

“There is a lot we don’t know about what actually happens under dense tree-covered areas,” Egerstedt said. “Most of the time SlothBot will be just hanging out there, and every now and then it will move into a sunny spot to recharge the battery.”

The researchers also hope to test SlothBot in a cacao plantation in Costa Rica that is already home to real sloths. “The cables used to move cacao have become a sloth superhighway because the animals find them useful for moving around,” Egerstedt says. “If all goes well, we will deploy SlothBots along the cables to monitor the sloths.”

Egerstedt is known for developing algorithms that drive swarms of small wheeled or flying robots. But during a visit to Costa Rica, he became interested in sloths and began developing what he calls “a theory of slowness.” The theory is based on the benefits of energy efficiency.

“If you are doing things such as environmental monitoring, you want to be out in the forest for months,” Egerstedt says. “That changes the way you think about control systems at a high level.”

Flying robots are already used for environmental monitoring, but their high energy needs mean they cannot linger for long. Wheeled robots get by with less energy but can get stuck in mud or be hampered by tree roots and cannot get a big-picture view from the ground.

“The thing that costs energy more than anything else is movement,” Egerstedt says. “Moving is much more expensive than sensing. Environmental robots should only move when they absolutely have to. We had to think about what that would be like.”

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