Bio-inspired robot climbs three-story building
April 14, 2008
Luckily, RiSE the robot isn't afraid of heights. Looking somewhat like a mutated scorpion - with six legs and 25-50 toes per foot - the robot uses technology inspired by geckos, squirrels, cockroaches, and other natural climbers to scale three-story buildings, among other feats.
Besides climbing, RiSE (which stands for Robots in Scansorial Environments) is the first legged machine capable of untethered locomotion on both the ground and vertical terrain, say its designers. RiSE is the product of a collaboration of several institutions, including the Illinois Institute of Technology (IIT), Carnegie Mellon University, Boston Dynamics Inc., Stanford University, the University of California-Berkeley, and the University of Pennsylvania. The group, under lead author M. J. Spenko of IIT, recently published their latest research on RiSE in the Journal of Field Robotics.
RiSE is unique, the researchers explain, in its versatility. It surpasses other more specialized robots in its ability to conquer a wide variety of terrains, from flat to pitched, rough to smooth, and dusty to slick, due to its adaptable feet. Some day, its climbing versatility could make it useful for surveillance, hazard removal, maintenance, and disaster relief applications.
Some of the vertical surfaces RiSE has climbed include buildings such as brick, stucco, crushed stone, cinderblock, and trees such as oak, eucalyptus, pine, and redwood. The robot, which has a weight of 3.8-kg (8.4-lb), can achieve speeds of up to 4 cm/s (1.6 in/s), and the researchers have set a target speed for it of 0.25 m/s (10 in/s).
RiSE is remotely controlled by a human operator that issues speed and turning commands. The robot carries three onboard lithium polymer battery packs to power the control and motor circuitry, giving it more than 45 minutes of run-time.
When climbing vertically, a climber - whether it be robot, animal, or human - must continually pull itself inward toward the wall while propelling itself against gravity, the researchers explain. RiSE uses a variety of animal tricks to achieve these motions. For example, it has large claws like bears and cats, allowing it to dig into softer surfaces like trees.
It also has spines (tiny fishhooks), such as those on insect legs, that allow it to climb hard, rough surfaces. The spines work by sliding and catching on tiny irregularities (such as in concrete) so that the friction between the spine tip and surface gives the robot a grip to pull itself inward. Its number of toes is related to the thickness of the spines (between 15 and 25 micrometers) that are used for different textures. The robot can also use an adhesive bonding - inspired by lizards, frogs, and insects - for tackling hard, smooth surfaces. Finally, for walking on flat surfaces, the hexapod is fitted with spherical rubber boots on its feet.
RiSE's physical features also take inspiration from nature. Its long body assumes a flattened posture where its center of mass is held close to the surface (often seen in squirrels) to keep it from falling. The researchers put the robot's heavy electronics - its batteries and motors, which make up 55% of its mass - on its underside, so that they're just a few centimeters from the wall when climbing.
RiSE's six legs, like those of insects, provide extra safety: the front legs are designed to pull inward, while the rear legs push out and up. If the front legs can't pull close enough, the middle legs can provide the additional pull-in force. Its long body and tail also help to reduce the required pull-in force, with its tail held close against the wall. With six legs, the robot can choose from a wide variety of gaits and speeds, from quick scittering to a "pentapedal crawl," where only one foot is removed from the surface at a time.
Despite RiSE's precise measurements, it's still inevitable that the robot will slip up once in a while. For example, sometimes a foot fails to attach to the climbing surface due to an irregularity, which could break the critical chain of steps in its gait. To address this challenge, the robot has foot sensors that indicate when a foot has made or lost contact with a surface. When it realizes that its foot has lost contact, RiSE paws the wall like a cat or dog, quickly recirculating its foot in an attempt to reattach it to the climbing surface.
In the future, the researchers plan to improve RiSE's power-to-weight ratio to enable it to climb faster and longer with less energy. The scientists hope to decrease RiSE's weight from the current 3.8 kg to 1.5 kg (5.5 lbs), through a combination of simplifying its onboard electronics and using lightweight custom motor and gearbox designs. Hopefully, these changes will help RiSE meet its target speed of 0.25 m/s (10 in/s) while climbing. (RiSE has achieved this target speed on carpeted walls in a previous study.)
Other future improvements the researchers have in mind include equipping RiSE's body with sensors or antennae to provide information on irregular surfaces, and adding acceleration sensors to its feet so that the spines can act as a styli to sense surface roughness. The team also hopes to improve the robot's autonomous abilities, enabling it to switch between gaits and plan its routes, and ideally eliminate the need for human guidance.
More information: Spenko, M. J.; Haynes, G. C.; Saunders, J. A.; Cutkosky, M. R.; Rizzi, A. A.; Full, R. J.; Koditschek, D. E. "Biologically Inspired Climbing with a Hexapedal Robot." Journal of Field Robotics 25(4-5), 223-242 (2008)
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