by Mark Luedtke
Introduction
Room 026 doesn't look special. The windowless lab in the basement of the Russ Engineering Center at Wright State University with the drab walls and black lab stations looks like any other college engineering lab, but a detailed look past the clutter of plastic gears, tiny motors and tools on the work tables reveals something that doesn't exist anywhere else in the world - tiny, artificial dragonfly wings. Under the direction of Assistant Professor Dr. Haibo Dong, twelve mechanical and material engineering seniors just designed, built and demonstrated a proof of concept model of a robot dragonfly in room 026. Dayton is once again hosting the leaders in revolutionary flight technology.
As far back as literature informs, man dreamed of soaring like a bird. The Wright brothers made that possible. But birds aren't the only flyers in nature that inspire men. Dr. Dong considers the Wright brothers to be the epitome of engineers, but he took his inspiration for this project from nature and his education in aeronautical engineering. Before joining Wright State in 2006, Dr. Dong researched bio-hydrodynamics of swimming fish and applied that knowledge to autonomous undersea robots. But once he landed in Dayton, his focus turned to dragonflies. When asked why, he replies, "I just have tons of ideas for some reason." Maybe it's something in the water. Or more accurately something in the air. According to Dr. Dong, the grassy fields around Wright State are teaming with dragonflies.
Background on Flying Robots
Because of the war in Afghanistan and the lawless areas of Pakistan, the word drone has become commonplace in American lexicon. Predator drones spy on Taliban and al Qaeda operatives, and pilots operating the vehicles by remote control half a world away drop bombs on suspected enemy leaders. The value of these large, fixed-wing robot fliers is well known. They've even been deployed over the Mexican border. US troops also utilize smaller drones to survey the battlefield. But researchers envision an entire new class of missions for much smaller flying robots called Micro Air Vehicles (MAVs), a subclass of which has recently been dubbed Nano Air Vehicles (NAVs). As Dr. Dong told Desktop Engineering, "Any time you can use robotics instead of people to gather information in areas that may be unstable, toxic, or hard to reach, you minimize the risk to public safety workers. And any time you can use robotics in spaces that are too dangerous or too small for people to enter, you create an opportunity to prevent a catastrophe that might otherwise have occurred, or you create a chance for rescue where there might otherwise have been no hope."
Because fixed-wing aircraft can't hover and have poor maneuverability and rotary aircraft are too noisy for missions requiring stealth, flapping-wing craft have become the focus of NAVs. Dr. Dong calls the most popular class of flapping-wing craft clappers because they have two wings on each side of the craft that clap together like hands clapping. Laying claim to the world's smallest aircraft equipped with a camera, the Delfy Micro was developed by a four man team at Delft University of Technology in the Netherlands. Looking like a butterfly with an airplane tail, this NAV has a four inch wingspan, weighs just over three grams and can fly at five meters per second for over three minutes.
But there's a reason nature didn't develop mechanical designs like these - they're not power efficient. The future belongs to nature inspired designs. Harvard University engineers have developed a NAV modeled on a fly which is about the size of horsefly, but to make it that small, they had to power it by tether. The Defense Advanced Research Projects Agency (DARPA) recently awarded Aeronvironment in Monrovia California a $2.1 million contract extension after engineers demonstrated a NAV modeled on a hummingbird that flew for 20 seconds.
Dr. Dong hopes to outperform all these robots by modeling his robot on the king of flying insects: the dragonfly. By flapping two pairs of wings at independent frequencies, curving the wings, and with subtle body movements, the dragonfly can hover, move forward and backward, up and down, and side to side. Dragonflies use significantly less energy to manipulate their body weight relative to birds. They intercept their prey in flight. The Dragonflyer has the potential to fly faster and longer, maneuver better and carry more weight than these other robots - all in a smaller package.
The Dragonflyer Project
When Dr. Dong's students signed up for this senior project, they probably didn't expect they'd spend so much time chasing dragonflies, but they did. Much of Dr. Dong's funding comes from an Air Force Research Labs (AFRL) unit at Wright Patterson Air Force Base, and it provided a pair of high speed cameras to video dragonflies in the lab from two different angles. At first the students kept the dragonflies in an upside down aquarium, but they quickly discovered the dragonflies were cooperative test subjects. In the absence of any predators or food to hunt, they would rest on a perch so the aquarium became unnecessary. Unfortunately, because the students repeatedly agitated them to fly, recaptured them, then repeated the cycle many times during a day, the exhausted dragonflies couldn't survive the night. The team adopted a catch, film and release strategy to insure they had plenty of dragonflies to capture and record every day.
Tools and techniques to build and analyze tiny, fast devices like the Dragonflyer are in their infancy, so the students had to learn several new technologies. The high-speed videos were fed into a new computational fluid dynamics (CFD) program which created 3D video models of the vortexes and air flows created by the flapping wings. The seniors spent most of the winter quarter studying the raw videos and the CFD videos so they could understand how the dragonfly maneuvered. The videos also work great as a recruiting tool, so Dr. Dong will have no shortage of student-engineers. After all this observation, it was time for subteams to build the three pieces of the proof-of-concept model - wings, actuator and tail - about 50 percent larger than an actual dragonfly.
Matthew Mills, Wesley Moosman, Joe Parsley and Cody Wright had the task of developing artificial dragonfly wings that weighed less than a gram each, that deformed like the dragonfly wing (camber) and had comparable structural integrity. Through a process of trial and error, these students used carbon fiber tow, ultra-think polyester film, and resin to produce wings that met their size, weight and camber design goals.
The task of designing an actuator to independently control both pairs of wings, flap both faster than 25 times a second and which would weigh under ten grams and be smaller than five cubic centimeters was assigned to Asela Benthara, Adam Harp, Conrad Jett, and Rich Martin. To make the design independent of a tether, the team chose to use tiny gears and motors. They used an amazing piece of technology, a 3D printer device that fabricates plastic pieces from technical specifications, to implement their increasingly sophisticated designs, ultimately meeting their design goals.
Zach Votaw, Adam Mays, Aron Brezina and Andy Walker set out to prove they could maneuver the Dragonflyer by manipulating a tail that lacked the traditional control surfaces of an airplane like a dragonfly does. They purchased a WowWee dragonfly toy, a form of clapper, and replaced the radio controller and tail. The flexible tissue tail design with no horizontal stabilizer ultimately settled on by the team enabled the WowWee to fly more level and turn in a tighter radius, proving they could better maneuver the aircraft through center of gravity manipulation - bending the tail - than with a control surface.
At the end of May, the Wright State assembled the three parts, added a battery and radio control receiver and successfully demonstrated the Dragonflyer proof-of-concept at their design review on June 5th, meeting the schedule and cost goals. But no engineering project is truly revolutionary. Of great benefit to Dr. Dong's students was the previous work developing a clapping MAV by Wright State professor Dr. George Huang's students, and they used his leading-edge equipment to produce their model.
What's Next?
Analysis, refinement and miniaturization. The performance of the design must be evaluated as a unit in a wind tunnel. The wings have yet to be analyzed under load. Friction is a major impediment to the efficient operation of the actuator. Some parts must be fabricated in metal to reduce friction and increase rigidity using another fantastic machine that cuts simple metal structures with wire. The model bends the tail with fishing string, which isn't practical. The designers suggest using smart materials that contract like muscles, but they're expensive. Then the design must be shrunk to the size of an actual dragonfly. Dr. Dong's goal is to demonstrate an actual sized Dragonflyer in flight in nine months.
And the project doesn't stop there. Dr. Dong communicates with biologists, roboticists and computer vision experts as part of his long-term vision to develop Dragonflyers that can navigate independently and operate in swarms to meet mission objectives. And improved manufacturing techniques are critical. Manually assembling these robots from such tiny parts while looking through a magnifying glass is less than optimal to say the least. Dr. Dong hopes to see a commercial product in five years.
As for the students, their future looks bright. After the design review, while they enjoyed that treat coveted by all college students - free pizza - pride out-dueled relief and exhaustion on their faces. This project gave them expertise that few other engineers can claim in what is sure to become a booming, new technology market in the next few years as products are commercialized. They know about the $2.1 million contract Aeronvironment won.
And the future of flight looks bright for Dayton. The Dragonflyer, a four-winged flapping robot, will be the most sophisticated NAV in the world. Maybe one day room 026 will be a historical landmark.
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