A system for environmental monitoring and precision agriculture takes a cue from the sloth - suggesting slow and energy-efficient can be better than fast and always needing a recharge.

“SlothBot” moves only when it has to measure environmental changes—such as weather and chemical factors in the environment—observed only with a long-term presence. It gets its power from pair of photovoltaic panels and is designed to linger in the forest canopy continuously for months.

"The life of a sloth is pretty slow-moving..."

Scientists described the proof-of-concept hyper-efficient robot at the International Conference on Robotics and Automation in Montreal.

“In robotics, it seems we are always pushing for faster, more agile, and more extreme robots,” says Magnus Egerstedt, chair of the School of Electrical and Computer Engineering at Georgia Institute of Technology 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.”

Hanging on

Based on what Egerstedt calls the “theory of slowness,” graduate research assistant Gennaro Notomista designed SlothBot with Yousef Emam, using 3D-printed parts for the gearing and wire-switching mechanisms needed to crawl through a network of wires in the trees. The greatest challenge for a wire-crawling robot is switching from one cable to another without falling, Notomista says.

Image: Georgia Institute of Technology

“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 with a mounted tire. 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. Next, a new 3D-printed shell—that makes the robot look more like a sloth—will protect 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 a SlothBot monitoring conditions as early as this fall.

Slow and steady

The name SlothBot is not a coincidence. Real-life sloths are small mammals that live in 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, an associate professor in the forest & wildlife ecology department at the University of Wisconsin-Madison, who consulted with the Georgia Tech team on the project.

“The nice thing about a very slow life history is that you don’t really need a lot of energy input. You can have a long duration and persistence in a limited area with very little energy inputs over a long period of time.”

That’s exactly what the researchers say they expect from SlothBot.

“There is a lot we don’t know about what actually happens under dense tree-covered areas,” Egerstedt says. “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.”

Sloth superhighway

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

Egerstedt develops 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 his “theory of slowness” with Ron Arkin, professor in the School of Interactive Computing at Georgia Tech. The theory leverages the benefits of energy efficiency.

“If you are doing things like 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 can get by with less energy, but they 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 or thinking. For environmental robots, you should only move when you absolutely have to. We had to think about what that would be like.”

“It is great to see a robot inspired by the biology of sloths,” Pauli says. “It has been fun to share how sloths and other organisms that live in these ecosystems for long periods of time live their lives. It will be interesting to see robots mirroring what we see in natural ecological communities.”

The US Office of Naval Research sponsored the work. The content is solely the responsibility of the authors and does not necessarily represent the official views of the ONR.