image: Left to right: University of Toronto PhD student Jeeraphat (Owen) Kledkruemas, Professor Pakpong Chirarattananon, and Song Li, a PhD student from the City University of Hong Kong on academic exchange at University of Toronto Engineering, demonstrating two different versions of the ‘Hopcopter’, a one-legged, hopping robot with a range of applications. (photo by Aaron Demeter / University of Toronto Engineering)
Credit: photo by Aaron Demeter / University of Toronto Engineering
A team of University of Toronto Engineering researchers has developed a flexible foot pad for the ‘Hopcopter’ — a one-legged, hopping robot they developed — significantly enhancing its performance on sand, ice and other difficult terrain.
The Hopcopter was designed to carry out a range of missions, such as search and rescue, remote infrastructure inspections and perhaps even interplanetary exploration. Its unusual mode of locomotion could provide important advantages over more common robotic designs, such as wheeled vehicles, flying drones or even four-legged robotic dogs.
“Drones are very familiar these days, and while they do have a lot of advantages, they also have some drawbacks,” says Professor Pakpong Chirarattananon, senior author on a paper published in Advanced Intelligent Systems(opens in new tab) that describes the new innovation.
“On the plus side, drones are relatively cheap to produce, they can fly over any kind of terrain and they are great for photography and videography. But because they need to be light, they aren’t so good at carrying lots of cargo, and their range is limited by how much fuel they can carry.”
“On the other end of the spectrum, you have wheeled or legged robots. Weight isn’t such a factor, so they can carry a lot more, and travel further. But they are much more expensive, and they can’t always handle rough terrain. There’s still a gap somewhere in between for a new kind of robot design.”
Chirarattananon’s team of researchers call themselves the Convergent Locomotion, Intelligent Mechanisms and Bio-inspired robotics lab (CLIMB)(opens in new tab). They look to nature as a model for how to design robots that strike the right balance between factors such as range, fuel efficiency, cost and cargo capacity.
The Hopcopter is one of these, inspired by the behaviour of animals such as birds.
“Birds can fly, but if you look at how they actually behave, they’re not constantly in the air,” says Chirarattananon.
“Instead, they flit from one location to another, perching and resting for long periods in between. Sometimes they even hop along the ground, using their wings sparingly each time. They conserve their energy, only using it when they need to.”
Song Li, a PhD student from the City University of Hong Kong and co-author of the paper, who is doing an academic exchange at MIE, played a key role in developing the Hopcopter. It’s essentially a traditional quadcopter-style drone perched on top of a single large, spring-loaded foot.
“The long leg with the center of mass high above the ground, along with pre-stretched rubber bands to counteract the effect of gravity and other forces, makes this design easier to model and control than other hopping robots,” says PhD student Jeeraphat (Owen) Kledkruemas, lead author on the new paper.
“The hopping motion enables it to easily bound over obstacles that would stop most robots equipped with legs or wheels, while still conserving energy and carrying more weight than a standard drone.”
But while the original Hopcopter was great at traversing flat concrete or fine gravel, there were still some types of terrain that caused problems.
“If it landed on something at a steep enough angle, or something slippery like ice, the foot would slip and it would lose balance,” says Kledkruemas.
“It also had a problem with sand or other soft surfaces: the foot would just sink down and get stuck.”
To overcome this problem, Kledkruemas created a foot pad that spreads the weight of the drone over a larger surface area, similar to how a snowshoe prevents its wearer from sinking down into the snow.
The new foot pad is also equipped with a spherical joint that enables it to slant in any direction, matching the angle of the whatever surface it encounters. A series of rubber bands provide tension that snaps the foot back into position after each hop.
The bottom of the foot pad is also covered in short spikes that provide additional traction, like the crampons used by ice climbers.
“These improvements make it possible to hop on ice and sand,” says Kledkruemas.
“They reduce the take-off error by up to 66% while improving the efficiency by up to 64%. They also reduce the performance variation across terrains by 84% — in other words, the new Hopcopter performs almost as well on difficult terrain as it does on smooth terrain.”
Going forward, the team plans to develop autonomous navigation for the Hopcopter and have it take on ever bigger challenges, demonstrating its ability to go where other robots currently cannot.
“This improvement enables us to bring this robot out of the lab and into the real world,” says Chirarattananon.
“We imagine it being used to conduct search and rescue after natural disasters, or inspect remote infrastructure such as pipelines or mining sites. We even dream of exploring places like Mars, where the atmosphere is too thin for most kinds of drones. There are lots of exciting possibilities.”
Journal
Advanced Intelligent Systems