A decade-long Harvard project produces the smaller winged robot ever made, which flaps its wings at 120 times per second.
Article copied from Robotic housefly Buzzes to Life in Popular Mechanics.Modeled after a housefly, the tiny robot weighs less than a tenth of a gram and is about half the size of a paperclip. Its two delicate wings can flap independently at up to 120 times per second. At that speed they're barely even visible to the human eye.
"The motivation was to explore basic research questions about how insects fly, and to apply those lessons to making very small mechanical devices," researcher Kevin Y. Ma tells PM. The scientists chose flies, he says, because of their extreme maneuverability and agility. Building robots that duplicate a fly's aerial talents could let scientists design tiny machines that monitor the environment for certain chemicals, aid in search-and-rescue missions in collapsed buildings, or even aid in the pollination of crops as artificial bees. That's all down the road, Ma says. "It's an exciting challenge, but we're really interested in the design process, and what we can learn from it."
One breakthrough
needed to build such a small flying bot was a new manufacturing process.
Ordinary ways to make stuff were either too big or too small for the scale of
an insect-size robot. "Traditionally," Ma says, "you have a nuts-and-bolts
manufacturing process. But our robot is the size of a bolt, so we can't really
use that." On the other end of the spectrum are microelectromechanical
systems, which are used for manufacturing cell phone circuits and other very
small mechanical structures. But this is for devices on the scale of
micrometers, and the Harvard team wanted to build a structure with features on
the order of a millimeter to a centimeter—10 or 100 times larger than that.
The answer, Ma says, is to make 2D structures and fold them into 3D—a little like origami. He says this technique is becoming widespread in other fields, where engineers are using it to build instruments for laparoscopic surgery, for example. In the manufacturing process, thin layers of material (in the case of the flying robot, carbon fiber–reinforced composites) are laser cut and stacked, then fused into a single flat piece. By using a combination of materials, the designer can create structures that have both rigid beams and flexible joints, which unfold into a 3D structure like a pop-up book. The insect has five layers of carbon fiber, two plastic layers to provide flexible joints, two brass layers for locking the final 3D structure into place, one layer of titanium to mimic insect wings, and two ceramic plates to actuate them.
But then there's the issue of power and computing speed. Current prototypes of the fly bot are tethered to a power source by a thin cable and controlled by a connected computer. There just aren't fuel cells or computational processors that can fit on the robot's tiny frame and operate efficiently. To fulfill their potential, these mini-machines need to go out in the world without a leash. With current tech, researchers estimate only a few minutes of flight using onboard power systems small enough not to hinder movement. The team hopes that high density fuel cells will get even smaller in the coming years and could serve as onboard battery packs.
Meanwhile, biologists on the team continue to study living flies, hoping to better understand how they perform such impressive aerobatics using the tiniest of brains—another quality future robots will hopefully share with them. Real houseflies use constant wing movement (reaching nearly 200 flaps per second) to maintain flight. Flies use three different aerodynamic mechanisms to stay airborne: When an insect sweeps its wing forward, it creates a vortex of air above them, creating lift. When the wing rotates backward, air is pulled over the top faster than the bottom, producing a force called a backspin—similar to the spin that makes a tennis ball stay in the air. And when the wing changes direction, it passes through the vortex created by the opposite stroke, extracting one last bit of energy and lift from it. Flies change direction so quickly because their wings move independently, allowing them to lift one higher than the other and steer.
The robot, unlike some previous prototypes, also has independent wings. Made out of ceramic, the artificial flight muscles rely on piezoelectric movement—the property that makes materials like ceramic expand and contract with the application of an electric field. Plastic hinges translate these tiny movements into flaps of a wing, and a control system commands rotational motions separately in each.
While their tethers keep them from flying with quite the finesse of a real bug, the robots did well in lab flight tests—the researchers were able to demonstrate stable hovering at a fixed point (with position errors of one body length of the robot) and sustained flights of longer than 20 seconds without any crashes. They were also able to make the robots fly laterally between two fixed points.
In a Harvard press release, project leader Robert J. Wood emphasized that this study is just the beginning. "Now that we've got this unique platform," he said, "there are dozens of tests that we're starting to do, including more aggressive control maneuvers and landing."
Read more: Robotic Housefly Buzzes to Life - Popular Mechanics
The answer, Ma says, is to make 2D structures and fold them into 3D—a little like origami. He says this technique is becoming widespread in other fields, where engineers are using it to build instruments for laparoscopic surgery, for example. In the manufacturing process, thin layers of material (in the case of the flying robot, carbon fiber–reinforced composites) are laser cut and stacked, then fused into a single flat piece. By using a combination of materials, the designer can create structures that have both rigid beams and flexible joints, which unfold into a 3D structure like a pop-up book. The insect has five layers of carbon fiber, two plastic layers to provide flexible joints, two brass layers for locking the final 3D structure into place, one layer of titanium to mimic insect wings, and two ceramic plates to actuate them.
But then there's the issue of power and computing speed. Current prototypes of the fly bot are tethered to a power source by a thin cable and controlled by a connected computer. There just aren't fuel cells or computational processors that can fit on the robot's tiny frame and operate efficiently. To fulfill their potential, these mini-machines need to go out in the world without a leash. With current tech, researchers estimate only a few minutes of flight using onboard power systems small enough not to hinder movement. The team hopes that high density fuel cells will get even smaller in the coming years and could serve as onboard battery packs.
Meanwhile, biologists on the team continue to study living flies, hoping to better understand how they perform such impressive aerobatics using the tiniest of brains—another quality future robots will hopefully share with them. Real houseflies use constant wing movement (reaching nearly 200 flaps per second) to maintain flight. Flies use three different aerodynamic mechanisms to stay airborne: When an insect sweeps its wing forward, it creates a vortex of air above them, creating lift. When the wing rotates backward, air is pulled over the top faster than the bottom, producing a force called a backspin—similar to the spin that makes a tennis ball stay in the air. And when the wing changes direction, it passes through the vortex created by the opposite stroke, extracting one last bit of energy and lift from it. Flies change direction so quickly because their wings move independently, allowing them to lift one higher than the other and steer.
The robot, unlike some previous prototypes, also has independent wings. Made out of ceramic, the artificial flight muscles rely on piezoelectric movement—the property that makes materials like ceramic expand and contract with the application of an electric field. Plastic hinges translate these tiny movements into flaps of a wing, and a control system commands rotational motions separately in each.
While their tethers keep them from flying with quite the finesse of a real bug, the robots did well in lab flight tests—the researchers were able to demonstrate stable hovering at a fixed point (with position errors of one body length of the robot) and sustained flights of longer than 20 seconds without any crashes. They were also able to make the robots fly laterally between two fixed points.
In a Harvard press release, project leader Robert J. Wood emphasized that this study is just the beginning. "Now that we've got this unique platform," he said, "there are dozens of tests that we're starting to do, including more aggressive control maneuvers and landing."
Read more: Robotic Housefly Buzzes to Life - Popular Mechanics
