Improving drone performance in headwinds

Multi-rotors have gotten much smaller since the turn of the century, and they have many uses, including for inspection, surveillance and transportation. A multi-rotor setup allows for both vertical takeoff and hover in calm conditions, but they are unstable in wind.  Engineers from Tohoku University, Japan, have shown that angling the rotor blades of a quad-rotor unmanned aerial vehicles by just 20 degrees can reduce pitching by a quarter.

Credit: Hikaru Otsuka

Pitching can occur because of three factors: the drag of the body, the asymmetry induced flow distribution on the rotor with the wind, and rotor thrust difference between the front and rear rotors. The team first estimated the effects of the wake of the front rotors on the rear, then isolated the rotors from the vehicle and measured the effect of different angles in a low-speed wind tunnel. They show that angling the rotors to the outer side by 75 degrees kept the airflow passing each rotor blade isolated, but increasing the angle to 90 or above meant the wake of the front rotors affected the rear.

Then they analyzed how this translated to a complete quad-rotor with all four rotors working together. In the wind tunnel, the team tested various angles of rotor attachment to the quadrotor and the effect on pitching moment generation. They measured the effects of outward and inward tilting of the rotor blades for five different angles. They found that rotor tilting by 20 to the outer side degrades the pitch of the vehicle by 26%.

Source (Tohoku University. “Improving drone performance in headwinds: Stability of unmanned aerial vehicles in heavy winds can be improved through rotor placement and angle.” ScienceDaily. ScienceDaily, 9 February 2018.)

Original paper: Otsuka, H., Sasaki, D. and Nagatani, K., 2018. Reduction of the head-up pitching moment of small quad-rotor unmanned aerial vehicles in uniform flow. International Journal of Micro Air Vehicles10(1), pp.85-105.

Novel 3-D printing method embeds sensing capabilities

Inspired by our bodies’ sensory capabilities, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences and the Wyss Institute for Biologically Inspired Engineering have developed a platform for creating soft robots with embedded sensors that can sense movement, pressure, touch, and even temperature. Integrating sensors within soft robots has been difficult in part because most sensors, such as those used in traditional electronics, are rigid. To address this challenge, the researchers developed an organic ionic liquid-based conductive ink that can be 3D printed within the soft elastomer matrices that comprise most soft robots.

Credit: Ryan L. Truby/Harvard University

To fabricate the device, the researchers relied on an established 3D printing technique developed in the lab of Jennifer Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at SEAS and Core Faculty Member of the Wyss Institute. The technique — known as embedded 3D printing — seamlessly and quickly integrates multiple features and materials within a single soft body. To test the sensors, the team printed a soft robotic gripper composed of three soft fingers or actuators. The researchers tested the gripper’s ability to sense inflation pressure, curvature, contact, and temperature. They embedded multiple contact sensors, so the gripper could sense light and deep touches.

Source (Harvard John A. Paulson School of Engineering and Applied Sciences. “Novel 3-D printing method embeds sensing capabilities within robotic actuators: Soft robots that can sense touch, pressure, movement and temperature.” ScienceDaily. ScienceDaily, 28 February 2018.)

Original paper: Truby, R.L., Wehner, M., Grosskopf, A.K., Vogt, D.M., Uzel, S.G., Wood, R.J. and Lewis, J.A., 2018. Soft somatosensitive actuators via embedded 3D printing. Advanced Materials30(15), p.1706383.