Engineers at the University of Toronto have created a flexible pad for the "Hopcopter," a one-legged hopping robot they developed earlier. The new addition noticeably improves its performance on sand, ice and other difficult surfaces.
The Hopcopter is intended for search-and-rescue operations, remote infrastructure inspection and possibly even exploration of other planets. Its unusual mode of locomotion could offer advantages over wheeled vehicles, flying drones and quadruped robots.
"Drones are commonplace today, they have many advantages, but also drawbacks," says Professor Pakpong Chirarattananon, senior author of a paper in the journal Advanced Intelligent Systems. "They are relatively cheap, fly over any terrain and are good for filming. But to be light, they carry cargo poorly, and their range is limited by fuel supply."
"On the other hand, wheeled and legged robots are less sensitive to weight, so they carry more and travel farther. But they are more expensive and do not always cope with rough terrain. Between these extremes there remains a niche for a new type of robot," he adds.
The CLIMB lab (Convergent Locomotion, Intelligent Mechanisms and Bio-inspired robotics) looks for models in nature. The Hopcopter is inspired by birds: they are not constantly in the air but flit from place to place, resting for long periods and sometimes hopping, saving energy.
Structurally it is an ordinary quadcopter mounted on one large springy leg. "The long leg with a high center of mass and pre-stretched rubber bands that counteract gravity and other forces simplify modeling and control compared with other hopping robots," explains lead author Jirapat (Owen) Kledkruemas.
Hopping lets it clear obstacles that would stop most wheeled and legged machines, while saving energy and carrying more weight than a standard drone. But on a sloped or slippery surface such as ice the leg slipped and the robot lost balance, and on sand or soft ground it sank.
The new pad distributes weight over a larger area, the way snowshoes keep you from sinking into snow. A hinged mount lets it tilt in any direction to match the surface angle, rubber bands return the leg to its starting position after a jump, and short spikes on the sole improve grip, like the crampons of ice climbers.
According to Kledkruemas, the improvements reduce takeoff error by up to 66% and raise efficiency by up to 64%. The spread of characteristics between surface types is reduced by 84%: on difficult ground the robot performs almost as it does on flat terrain.
Going forward, the team plans to work on autonomous navigation and more complex tasks. "This improvement allows us to take the robot out of the lab into the real world," says Chirarattananon. "We see it in search-and-rescue work after natural disasters or in inspecting pipelines and mines. We also dream of exploring Mars, where the atmosphere is too thin for most drones."