A team of researchers from the Singapore University of Technology and Design have unveiled what they claim to be the world's first foldable single-actuary rotary-wing micro aerial vehicle — or F-SAM to its friends.
"In this work, a monocopter with a foldable, semi-rigid wing is proposed and its resulting flight performance is studied," the team explains in the paper's abstract. "The wing is non-rigid when not in flight and relies on centrifugal forces to become straightened during flight."
"The wing construction uses a special technique for its lightweight and semi-rigid design, and together with a purpose-designed autopilot board, the entire craft can be folded into a compact pocketable form factor, decreasing its footprint by 69 per cent. Furthermore, the proposed craft accomplishes a controllable flight in 5 degrees of freedom by using only one thrust unit."
The resulting design doesn't look much like a drone, but takes its inspiration from nature — specifically, the seeds of the Acer palmatum, which auto-rotate as they fall to spread themselves more widely. Unfolded, the curved multi-section single wing has a motor and propeller at one end and the electronics, including two batteries and a custom-built autopilot board, at the other.
The autopilot system itself is a custom control board built around SparkFun's MicroMod ecosystem, using a MicroMod ESP32 Processor Board to drive a payload including a pair of time-of-flight (ToF) sensors, a three-axis magnetometer, and a six-axis inertial measurement unit (IMU). Data captured are sent across the ESP32's Wi-Fi link to a remote system for analysis.
The segmented wing is designed to fold up on itself, rolling into a roughly triangular tube with the electronics on the outside and held in place by a band. When unwrapped, the machine remains foldable — until the motor kicks in and centrifugal force adds rigidity.
While the current design is entirely functional, its creators have ideas for how it could be improved. "Currently, F-SAM can be folded into a compact form and stored inside a container. However, it still requires a human to unfold it and either hand-launch it or put it on the floor to fly off," first author Shane Kyi Hla Win explains in an interview with IEEE Spectrum.
"In the future, we envision that F-SAM is put inside a container which has the mechanism (such as pressured gas) to catapult the folded unit into the air, which can begin unfolding immediately due to elastic materials used. The motor can initiate the spin which allows the wing to straighten out due to centrifugal forces."
The team's work has been published under open-access terms in the journal Bioinspiration & Biomimetics.