Spider-like robots that can scale walls with ease might be coming to a metropolis near you, if researchers at Harvard and Rolls-Royce have their way. A newly published paper in the journal Science Robotics details a system — dubbed Harvard Ambulatory MicroRobot with Electroadhesion, or HAMR-E for short — that uses electrostatic forces to grip horizontal, vertical, and even inverted metallic surfaces.

“The ability to climb greatly increases the reachable workspace of terrestrial robots, improving their utility for inspection and exploration tasks,” wrote the team of researchers from Harvard University’s Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences. “This is particularly desirable for small … robots operating in confined environments.”

HAMR-E is a retrofit of an existing robot — HAMR — that sports four limbs, weighs about 1.48 grams, and measures 4.5 centimeters long (a quarter of the length of a No. 2 pencil). In the course of the study, the paper’s coauthors affixed flexible electroadhesion pads to its “legs” and rotatable fiberglass-and-polyimide alignment ankles, each containing insulated copper electrodes wired to a power source. The climbing surface, meanwhile, was attached to an electrical ground, and when the bot’s pads were supplied with voltage, the resulting positive charge interacted with the wall’s negative charge to generate an attractive force.

It wasn’t as easy as it sounds. To prevent HAMR-E from getting stuck or losing its grip, the researchers had to implement a gait called a tripedal crawl, in which three of its legs remained in contact with the surface while one moved forward. As HAMR-E walked, voltage flowed to three of the legs and cut off voltage to one, alternating the flow as the quadrupedal robot moved forward. And they had to adopt a slightly different strategy for upside-down scenerios: HAMR-E’s front left leg lifted to move at the same time the back right leg pushed forward, counteracting the backward pitch created by the front leg lift.

Harvard HAMR-E

“Without this reach and push, we were able to go for less than five steps,” Neel Doshi, a coauthor on the paper, told Wired. “With these two parameters tuned appropriately, we’re able to walk for 80, 90 steps without random perturbations taking it off.”

In tests with 250 volts of electricity, HAMR-E was able to “walk” while hanging vertically a maximum of 215 steps at speeds of up to 1.2 millimeters per second. More impressively, on horizontal surfaces, it managed to travel 140 millimeters per second — roughly 0.31 miles per hour — and perform 180-degree turns.

HAMR-E won’t break robotic speed records anytime soon, needless to say, but the team envisions mechanisms like it being used to inspect the inside of commercial jet engines and other “high-value assets.” They’re already planning the next iteration of HAMR-E, which they say will be able to cling to surfaces without a tether thanks to more powerful adhesion pads that can support the weight of a small battery.

“Now that these robots can explore in three dimensions instead of just moving back and forth on a flat surface, there’s a whole new world that they can move around in and engage with,” first author Sébastien de Rivaz, a former research fellow at the Wyss Institute who now works at Apple, said in a statement. “They could one day enable non-invasive inspection of hard-to-reach areas of large machines, saving companies time and money and making those machines safer.”

Harvard isn’t the only institution developing walk-climbing robots. In another recent study, researchers led by Guoying Gu from Shanghai Jiao Tong University in China revealed a “tethered soft robot capable of climbing walls made of wood, paper, and glass” using a combination of artificial muscles and electro-adhesive feet.