University research and development projects prove composites drive innovation and solve problems.
Across the world, composites are being increasingly recognized as the material of the future. Helping to shape that belief is the cutting-edge research and development being conducted at universities and research centers.
In this issue, Composites Manufacturing highlights research projects at six American universities that demonstrate innovation and potential real-world applications. Imagine a world where recycled composites get a second life, bridges withstand earthquakes and robots contribute to rescue missions. Here’s a peek into some of the research projects trying to make these things – and more – a reality.
Project: Robotic cheetah made from CFRP
School: Massachusetts Institute of Technology (MIT)
Location: Cambridge, Mass.
Principal Investigator: Sangbae Kim
Armed with composite legs, feet and body frame, MIT’s pioneering robotic cheetah can run and jump in an extraordinarily animal-like and efficient manner. This is big news for robot research as most “legged” robots are quite slow, according to Sangbae Kim, associate professor of mechanical engineering at MIT.
Kim began the robotic cheetah project six years ago with the goal of developing fundamental technologies for transportation that will allow legged systems to replace or augment wheeled systems. This is important, he stresses, because most of the earth is covered with non-flat surfaces – from curbs and stairs to hills and mountains. Yet, he notes, our current foundational mode of transportation – wheeled vehicles – is best suited for flat surfaces.
Kim and his team began the project by studying animal biology and biomechanics. He points out that mountain goats can climb 70 degree slopes and lions can safely jump off heights equivalent to a three-story building. And they do so with material that is much weaker than engineered materials. For example, Kevlar® aramid fiber is 20 to 30 times stronger than tendons, says Kim.
“We have engineering material that far exceeds animal material, but somehow we cannot build machines like a gazelle or a deer – these very thin-legged animals that can run, jump and land and are still very robust,” he says. “We still don’t know how to build machines that can handle that kind of impact.”
The robotic cheetah required research in three main areas – its motor, control mechanism and structure. Kim and his team developed an electric motor optimized with a transmission and a light detecting and ranging (LIDAR) sensor system that allows the robot to “see” and autonomously jump over objects. The cheetah’s structure is made from composites.
Fabricated by ProTech Composites Inc. in Vancouver, Wash., the body frame is made of ½-inch thick carbon fiber high-density foam sandwich panel that is CNC milled to create its shape and to add mounting holes for aluminum fasteners. Kim selected this construction because it is both light and stiff.
Kim says it’s critical that the robot’s legs mimic the way that bones and tendons work together to reduce the stress of impact. The cheetah’s legs are made of a stiff, 3-D printed core made from a polycarbonate-ABS industrial thermoplastic (the bones) and bidirectional, woven carbon fiber and Kevlar® (the tendons). The woven reinforcements are soaked in super glue and hand-wrapped around the core.
Although Kim used epoxy resins and polyurethanes to build earlier versions of the legs, he now soaks the reinforcements in super glue before wrapping. “That’s a faster and easier way to create a surface composite on a 3-D printed part,” he explains. That’s especially important because the legs, which get the most wear-and-tear, need to be rebuilt every few days.
The cheetah’s feet have an outer GFRP skin – or ‘shoe’ – that is made using a 3-D printed mold, the lab’s vacuum chamber and room temperature vulcanizing polyurethane. This stiff outer shoe is then filled with a very soft rubber. The result is a tire-like structure that can absorb much of the impact when the cheetah lands. The legs and feet used to be fabricated in one piece, but because the legs have to be replaced frequently they are now fabricated separately and attached to the legs with zip ties.