Thanks to more effective artificial pollination, farmers will be able to grow fruit and vegetables in multi-story warehouses in the future, increasing yields while mitigating some of the harmful effects of agriculture on the environment.
To make this idea a reality, MIT researchers are developing robotic insects that could one day crawl out of mechanical hives and quickly perform precision pollination. But even the best insect-sized robots can’t match natural pollinators like bees in terms of strength, speed and maneuverability.
Now, inspired by the anatomy of these natural pollinators, scientists have changed their design, creating miniature, aerial robots that are much more agile and sturdy than previous versions.
The recent bots can hover in the air for about 1,000 seconds, more than 100 times longer than previously demonstrated. The robotic insect, which weighs less than a paper clip, can fly much faster than similar bots, performing acrobatic maneuvers such as double flips in the air.
The upgraded robot is designed to boost precision and agility in flight while minimizing mechanical stress on the bends of the artificial wings, enabling faster maneuvers, greater endurance and longer service life.
The recent design also provides enough free space for the robot to carry miniature batteries or sensors, which would allow it to fly independently outside the lab.
“The flight times we have demonstrated in this paper are probably longer than all the flight times our field has been able to accomplish with these robotic insects. With the increased durability and precision of this robot, we are approaching some very exciting applications, such as assisted pollination,” says Kevin Chen, associate professor in the Department of Electrical Engineering and Computer Science (EECS), head of the Pliable and Informatics Division of the Microrobotics Laboratory at the Research Laboratory for Electronics (RLE). and senior author of an open-access article on the recent project.
Chen is joined in the article by co-authors Suhan Kim and Yi-Hsuan Hsiao, who are both EECS graduate students; as well as EECS graduate Zhijian Ren and summer visiting student Jiashu Huang. Tests is published today in .
Increasing efficiency
Earlier versions of the insect robot consisted of four identical units, each with two wings, combined into a rectangular device about the size of a microcassette.
“But there is no insect that has eight wings. In our old design, the performance of each individual unit was always better than that of the assembled robot,” says Chen.
This drop in performance was partly due to the arrangement of the wings, which blew air into each other as they flapped, reducing the lift forces they generated.
The recent design cuts the robot in half. Each of the four identical units now has one flapping wing pointing away from the center of the robot, which stabilizes the wings and increases their lift. With half as many wings, this design also frees up space so the robot can carry electronics.
In addition, researchers have created more convoluted gears that connect the wings to actuators, the artificial muscles that flap them. These sturdy gears, which required the design of longer wing hinges, reduce mechanical stress that narrow the durability of previous versions.
“Compared to the old robot, we can now generate three times more steering torque than before, so we can perform very sophisticated and very accurate pathfinding flights,” Chen says.
However, even with these design innovations, there is still a gap between the best robot insects and real insects. For example, a bee has only two wings, yet it can make quick and controlled movements.
“Bees’ wings are precisely controlled by a very sophisticated set of muscles. This level of refinement really intrigues us, but we haven’t been able to replicate it yet,” he says.
Less load, more strength
The movement of the robot’s wings is powered by artificial muscles. These miniature, cushioned actuators are made of layers of elastomer sandwiched between two very slender carbon nanotube electrodes and then rolled into a cushioned cylinder. The actuators quickly compress and extend, creating a mechanical force that flaps the wings.
In previous designs, when actuator movements reached the extremely high frequencies needed for flight, the devices often began to buckle. This reduces the power and efficiency of the robot. The recent gears inhibit this bending and buckling movement, which reduces the load on the artificial muscles and allows them to apply more force to flap the wings.
Another recent design includes a long wing hinge that reduces torsional stresses that occur during the flapping movement of the wing. One of the biggest challenges was producing a hinge that is approximately 2 centimeters long and just 200 microns in diameter.
“If there is even a slight alignment problem during the manufacturing process, the wing hinge will be tilted rather than square, which affects the wing kinematics,” Chen says.
After many trials, the researchers perfected a multi-step laser cutting process that allowed them to precisely craft each wing hinge.
Once all four units are installed, the recent robot insect can hover in the air for over 1,000 seconds, which equates to almost 17 minutes, without showing any degradation in flight precision.
“When my student Nemo made this flight, he said it was the slowest 1,000 seconds he had ever spent in his entire life. The experiment was extremely stressful,” says Chen.
The recent robot also achieved an average speed of 35 centimeters per second, according to the fastest flight researchers, while performing somersaults and double flips. It can even precisely track the trajectory that marks MIT.
“Ultimately, we have shown that the flight is 100 times longer than anyone else in the field, so this is an extremely exciting result,” he says.
Hence, Chen and his students want to see how far they can take this recent project, with the goal of achieving a flight longer than 10,000 seconds.
They also want to improve the precision of the robots so they can land and take off from the center of the flower. In the longer term, researchers hope to install miniature batteries and sensors in aerial robots so they can fly and move outside the lab.
“This new robotic platform is a major achievement for our group and leads in many exciting directions. For example, incorporating sensors, batteries and computational capabilities into this robot will be a major topic in the next three to five years,” says Chen.
This research is funded in part by the US National Science Foundation and a Mathworks Fellowship.