Drawing inspiration from nature, SUTD researchers are pushing the limits of drone research.

Not too long ago, most people had little idea about what drones were and how they could be used. Their application was confined mostly to reconnaissance and military strikes. But today, drones are popular consumer electronic products, fulfilling a variety of commercial functions, from wedding and concert photography to eye-catching light shows in the sky.

Despite their current widespread usage, drones still plenty of room for improvement. Most consumer drones, for instance, are bulky and have more than one rotor, making it difficult for the power source to support prolonged flight. Thankfully, scientists are continuously improving drone technology to make compact and energy-efficient drones that are are easy to fly.

At the Singapore University of Technology and Design’s (SUTD) Aerial Innovation Research (AIR) laboratory, researchers are taking drone innovation up a notch by drawing inspiration from mother nature.

“Nature is usually very efficient as it has evolved for a long time,” said Foong Shaohui, Associate Professor at SUTD’s Engineering Product Development (EPD) pillar. “Hence, leveraging what mother nature has done usually is a very good starting point. If it has stood the test of time for thousands of years, then it must be pretty good!”

Here, we look at two of the most exciting nature-inspired drones at SUTD.

Flying SUTD’s avant-garde monocopters
A classic approach to reduce a drone’s size is to develop them as monocopters– devices with only one rotating blade. Nature-inspired monocopters have been around for decades, but the existing ones need at least two actuators to fly, explained Luke Soe Thura Win, Senior Research Assistant at SUTD’s EPD pillar. Actuators are mechanical devices that use power to move parts of the monocopter—its propeller, in this case.

SUTD researchers have simplified monocopters even further by developing the Single Actuator Monocopter (SAM), which needs only one actuator to move the rotor.

Like most monocopters, SAM draws cues from the winged seeds of samara fruits such as maple. These seeds are composed of a flat, papery wing anchored to a heavy, dry part at one end. Because of its unique structure, the winged samara seeds fall slowly to the ground after being released from a tree, spiraling on its way down. Unlike other monocopters, which use complex wing designs to improve flight stability, SAM stays true to the samara seed structure.

SAM consists of only a single wing, which at one end is attached to a power source and a tiny computer, and at the other, to a small propeller. Weighing only 60 grams, SAM is the simplest monocopter yet, which can achieve stable, energy-efficient and controllable flight, said Luke Thura.

More recently, Lake Thura, Assoc Prof Shaohui and their colleagues have improved SAM even further by developing a foldable version called F-SAM.

While their overall structures are similar, F-SAM’s wing is made up of a series of balsa panels. This makes F-SAM slightly heavier at 69 grams, but allows it to be rolled up and kept in a small container when not in use, making it more compact and portable than the basic SAM.

According to Assoc Prof Shaohui, his team is aiming to make F-SAM completely independent, looking for ways to deploy F-SAM from its container without human intervention.

“There are a few ways to do this,” he said. “The wing can be embedded with a mechanical spring which automatically unwraps the wing. Alternatively, by modifying the wing geometry and shape, we may be able to make use of aerodynamic forces to perform the unwrapping naturally.”

F-SAM can be deployed in obscure and unhabituated areas to monitor critical environmental parameters and variables such as temperature, solar irradiance, poaching detection.

Seed-inspired aerodynamic wing
Taking advantage of aerodynamic forces is central to another cutting-edge drone at the AIR lab: the Samara Autorotating Wing (SAW).

While both F-SAM and SAW have only one controllable actuator, SAW uses it in a very different way. Rather than moving a propeller, SAW’s actuator bends a flap in its wing, decreasing its surface area. Although SAW cannot launch itself from the ground, it is very useful in simplifying applications that need a single trip downward. For example, a parachute, which often requires people to handle complex mechanisms to control the parachute direction and speed.

However, it is exactly during this freefall that SAW’s key functionality shines. When the wing is completely spread out, the drone floats slowly to the ground much like how a samara seed does, spinning gracefully downward.

But when the situation calls for it, SAW is also able to dive quickly through the air —even in bad weather. “In some cases, such as pockets of rough weather, increasing vertical velocity may be favourable,” said Assoc Prof Shaohui. SAW allows users to switch between its slow-descent and diving modes on command, giving them a great degree of control over the drone.

“SAW can be useful for deployment of critical sensors in remote forests for detection of wild fires, as well as possibly being used to track global environmental parameters both in high altitudes and on the ground,” added Assoc Prof Shaohui, pointing out that SAW’s dive mode can also be activated to embed a sensor into the ground.

Moving forward, the AIR team hopes to build on the achievements of SAW and F-SAM to come up with even better nature-inspired drones. “We are constantly trying to push the limits of the samara inspired aerial crafts and we are also looking into operating and controlling a collaborative swarm of these systems,” said Assoc Prof Shaohui.

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