Researchers build flying robotic ‘tree helicopter’
(PhysOrg.com) — Many trees disperse their seeds by releasing “helicopters,” those single-winged seeds that are also called “samaras.” As these seeds fall to the ground, their wing causes them to swirl and spin in a process called autorotation, similar to man-made helicopters. In a new study, researchers have designed and built a mechanical samara whose dynamics are very similar to those of nature’s samaras. After testing the mechanical samara, the researchers then built a variety of remote-controlled robotic samaras with onboard power sources
A natural samara is positioned next to the smallest and lightest robotic samara constructed to date. The wing of the vehicle is similar in size to a natural samara wing. Image credit: Ulrich, et al.
The researchers, Evan Ulrich, Darryll Pines, and Sean Humbert from the University of Maryland, have published their study on the robotic samaras in a recent issue of Bioinspiration & Biomimetics. The idea for building a flying robotic device based on samaras originated several years ago, after researchers attempted to scale down full-size helicopters.
“Full-scale helicopters have a high aerodynamic efficiency,” Ulrich, a PhD candidate, told PhysOrg.com. “But the aerodynamic efficiency is disproportionate, so a scaled-down helicopter has stability issues and is unfeasible. Dr. Pines, my advisor, realized that the simplest system in nature that achieves vertical flight and can autorotate like a helicopter is the samara, which is a naturally stable system.”
After further investigating the samara in order to better understand its flight dynamics, the researchers found that the winged seed is also one of nature’s most efficient fliers. The samara is a monocopter, meaning it has a single wing. For this reason, the samara has no stationary frame of reference, unlike a two-winged helicopter, and appears to fall in a complex way. However, through free-fall testing, the researchers could quantitatively measure the samara’s flight dynamics and use this information to control the samara’s autorotation and flight path.
After designing and building a mechanical samara, the researchers measured its flight dynamics in free-fall by dropping it from a height of 12 meters. Then the scientists used this data to develop three different designs of powered robotic samaras, ranging in size from 7.5 cm to 0.5 m. In flight tests, they demonstrated that the carbon fiber-based robotic samaras could be remotely steered to a desired location by altering the wing pitch, which changes the radius at which the vehicles turn. The robotic samaras could also hover, climb, and translate.