Lightweight Whiskers for Tiny Drones Detect Micronewtons

Drone technology is drawing inspiration from myriad functions of animals in nature to operate in more efficient ways- this time around its whiskers. Animals of all shapes and sizes have whiskers of some sort. Whiskers are an efficient and effective method of short range sensing. Whiskers can also sense fluid flows (like the speed and direction of moving air or water), and they work even if it’s dark or foggy or smoky.

At ICRA last month, Pauline Pounds from the School of Information Technology and Electrical Engineering, University of Queensland in Brisbane, Australia, demonstrated a new whisker sensing system for drones. The whiskers are tiny, cheap, and sensitive enough to detect air pressure from objects even before they make physical contact. The research is published in IEEE Robotics and Automation Letters (Volume: 4 , Issue: 2, April 2019).

While LiDAR and cameras offer more useful data at longer ranges it calls for too much an expense or programming effort for very small or low budget drones- especially for simple functions or behaviors like not crashing into stuff.

Here’s how the researchers describe the system:

‘We are interested in translating the proven sensor utility of whiskers on ground platforms to hovering robots and drones— whiskers that can sense low-force contact with the environment such that the robot can maneuver to avoid more dangerous, high-force interactions. We are motivated by the task of navigating through dark, dusty, smoky, cramped spaces, or gusty, turbulent environments with micro-scale aircraft that cannot mount heavier sensors such as lidars.’

The easy to fabricate whisker fibers are just blobs of ABS plastic that are heated up and then drawn out into long thin fibers like taffy. The length and thickness of the whiskers can be modulated by adjusting the temperature and draw speed. The ABS blob at the base of each whisker is glued to a 3D-printed load plate, which is in turn attached to a triangular arrangement of force pads (actually encapsulated MEMS barometers). The force pads can be fabricated in bulk, so it’s straightforward to make a whole bunch of whiskers at once through a process that’s easy to automate. The material cost of a four-whisker array is about US$20, and the weight is just over 1.5 grams.

In a video demonstration this super sensitive whisker it is seen detecting forces as low as 3.33 micronewtons, meaning that the researchers had to be careful not to stand too close to the whiskers while making measurements since the force of their breathing would throw things off. This sensitivity allows the whiskers to detect the wave of air generated by objects moving towards them- if not in time for the drone to actually stop, but definitely in time for it to take other steps to protect itself, like cutting power to its motors. The whiskers can also be used to measure fluid flow (a proxy for velocity through the air), and of course, at slow speeds they work as contact sensors.

While the focus of this research has been on whiskers for micro-drone applications, it appears these could be fantastic sensors for a wide variety of robots, and especially for cheap robots.

In fact any small robots that operate in environments that are dark, dusty, or smoky could leverage these sensors to keep from running into things where far more expensive cameras and lidar systems would struggle. The next step will be mounting the whisker arrays on real drones to see how they perform.

Citation: Deer, William & E. I. Pounds, Pauline. (2019). Light-Weight Whiskers for Contact, Pre-Contact and Fluid Velocity Sensing. IEEE Robotics and Automation Letters. PP. 1-1. 10.1109/LRA.2019.2899215. https://ieeexplore.ieee.org/document/8641341