Boston’s aging sewers are crumbling – but it’s not exactly easy to send a human through them to pinpoint exactly where infrastructure updates are needed. Robots seem ripe to do the job, but rovers are too slow to navigate the enormous, maze-like system. Traditional drones with fast-rotating blades can’t fly inside incredibly narrow drain pipes because they generate turbulent flows which can cause them to crash. 

But researchers at Northeastern University aren’t discounting drones completely. Instead, they built a tiny drone that resembles a bat more than your traditional quadcopter — and it’s aptly named the Aerobat. After all, if bats can fly through the network of underground caves, a bat-style drone could do it too – while also serving potentially as the perfect solution to conducting sewer inspections. 

The Aerobat is a ‘bio-inspired’ drone, meaning it takes its shape from biological structures or processes (in this case, bats). It’s also considered a Micro Aerial Vehicle (MAV) because it’s just 20 grams (that’s lighter than a AA battery), and it was built by the SiliconSynapse Lab, which is a part of the Electrical and Computer Engineering (ECE) Department of Northeastern University in Boston.

Why is the Aerobat so important?

Boston is quite an old city, and naturally so is its infrastructure. Some of the hardest areas to inspect and repair are the sewers, as they remain unseen and difficult to access. Due to this inaccessibility, current sewer inspection methods rely heavily on wheeled robots which are extremely slow and costly methods; averaging 100 feet of inspection per day, they barely dent the over 1500 miles of Boston sewer pipes.

MAVs are expected to be vital in accelerating inspection timelines and reducing costs. Researchers say one Aerobat could accelerate inspection times by 10-100x. Once you deploy a swarm of Aerobats, that number could increase even further. Traditional MAVs such as quadcopters would struggle in a confined space such as a sewer system, so where traditional MAVs fail, Aerobat fills the need at hand.

Why a bat-inspired design?

Aerobat’s design is based on bat wings, strategically collapsing and expanding its wings to maximize lift generation. By taking a flapping-wing approach, Aerobat avoids producing powerful air jets like rotorcraft do. These air jets are problematic in confined spaces because they create vertical disturbances, making it difficult for drones to fly properly — and often leading to crashes. By being able to lift without powerful jets, Aerobat is set to fly inside underground sewer networks — not unlike real bats.

Copying a bat’s flight is no easy feat. A bat wing has 40 joints, and the Aerobat makers tried to replicate that in their own flight apparatus. Like bats, a single wingbeat in Aerobat’s flight is composed of a downstroke phase, where the drone’s wings are extended and swing down, and an upstroke phase, where the wings are collapsed and lifted up. Utilizing clever mechanism design allows Aerobat to be driven with a few actuators, minimizing overall weight while simultaneously maximizing lift force generated during each flapping cycle.

Read more: What’s the best drone for roof inspections?

Looking to the future

As the need to fix aging cities like Boston grows increasingly urgent, we need to come up with innovative solutions to bridge old structures with new technology and demands. Robotic initiatives such as Aerobat are proof that taking inspiration from nature could lead to smarter technology. These drones can make our residential spaces smarter, safer, more efficient, and closer to the materialization of the concept of smart cities.

-By Alireza Ramezani

Alireza Ramezani is an Assistant Professor of Electrical and Computer Engineering at the Northeastern University College of Engineering.

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