A new robot with two claws and a tail that sways like a pendulum is the first robot designed to move efficiently like human rock climbers or apes swinging through trees.

The small robot, named ROCR (pronounced "rocker"), can scramble up a carpeted, eight-foot wall in just over 15 seconds. A robot of this design could eventually be used for inspection, maintenance and surveillance, according to its makers.

But in the meantime, "probably the greatest short-term potential is as a teaching tool or as a really cool toy," said ROCR developer William Provancher, an assistant professor of mechanical engineering at the University of Utah.

In a study appearing this month in Transactions on Mechatronics, Provancher and his colleagues wrote that most climbing robots "are intended for maintenance or inspection in environments such as the exteriors of buildings, bridges or dams, storage tanks, nuclear facilities or reconnaissance within buildings."

Until now, such bots were designed not with efficiency in mind, but with a more basic goal: not falling off the wall they are climbing.

"While prior climbing robots have focused on issues such as speed, adhering to the wall, and deciding how and where to move, ROCR is the first to focus on climbing efficiently," Provancher said.

Getting there without wasted effort

One previous climbing robot has ascended about four times faster than ROCR, which can climb at 6.2 inches (15.7 centimeters) per second, but ROCR achieved 20 percent efficiency in climbing tests, "which is relatively impressive given that a car's engine is approximately 25 percent efficient," Provancher said.

The robot's efficiency is defined as the ratio of work performed in the act of climbing to the electrical energy consumed by the robot.

Other researchers have studied a variety of ways for climbing robots to stick to walls, including dry adhesives, microspines, so-called "dactyl" spines or large claws like ROCR's, suction cups, magnets, and even a mix of dry adhesive and claws to mimic wall-climbing geckos.

Now that various methods have been tried and proven for robots to climb a variety of wall surfaces, "if you are going to have a robot with versatility and mission-life, efficiency rises to the top of the list of things to focus on," Provancher said.

Nevertheless, "there's a lot more work to be done" before climbing robots are in common use, he added.

The shape of ROCR

Some previous climbing robots have been large, with two to eight legs. ROCR, in contrast, is small and lightweight: only 12.2 inches wide (31 centimeters), 18 inches (46 centimeters) long from top to bottom and weighing only 1.2 pounds (.54 kilogram).

The motor that powers the robot's tail as well as a curved, girder-like stabilizer bar are attached to the robot's upper body. This upper area also has two small, steel, hook-like claws that sink into a carpeted wall as the robot climbs. Without the stabilizer, ROCR's claws tended to move away from the wall as it climbed and it fell.

The motor drives a gear at the top of the tail, causing the tail to swing back and forth, which propels the robot upward. A battery is at the end of the tail and provides the mass that is necessary to swing the robot upward.

"ROCR alternatively grips the wall with one hand at a time and swings its tail, causing a center of gravity shift that raises its free hand, which then grips the climbing surface," the study said. "The hands swap gripping duties and ROCR swings its tail in the opposite direction."

ROCR is self-contained and autonomous, with a microcomputer, sensors and power electronics to execute desired tail motions to make it climb.

Looking to nature

Provancher said that to achieve efficiency, ROCR mimics animals and machines.

"It pursues this goal of efficiency with a design that mimics efficient systems both in nature and manmade," he said. "It mimics a gibbon swinging through the trees and a grandfather clock's pendulum, both of which are extremely efficient."

The researchers found it achieved the greatest efficiency when the tail swung back and forth 120 degrees (or 60 degrees to each side of straight down) at a rate of about 1.125 times per second and when the claws were spaced 4.9 inches (12.5 centimeters) apart.

Provancher said the study is the first to set a benchmark for the efficiency of climbing robots against which future models may be compared.

He said future work will include improving the robot's design, integrating more complex mechanisms for gripping to walls of various sorts, such as brick and sandstone, and investigating more complex ways of controlling the robot – all aimed at improving efficiency.

"Higher climbing efficiencies will extend the battery life of a self-contained, autonomous robot and expand the variety of tasks the robot can perform," Provancher said.

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