To many metal detecting is a task many, and most do, for one purpose: it offers a fun hobby. The hobby saw a massive surge in popularity during the COVID lockdown as people sought out safe and enjoyable outdoor activities.
However, with rewards come risks. Metal detecting is not free of danger – especially if you are searching for a ‘treasure’ across a historical battlefield. One such treasure that may contain unexploded ordnance is such as land mines.
Metal Detecting: Is it Safe?
Metal detecting is a thrilling but risky hobby. Especially if you’re wandering over the remnants of war. Approximately 12000 square kilometres of land worldwide is rendered useless and uninhabitable. Why? Because of the risk of buried explosives and dangerous chemicals.
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Every year, thousands lose their lives or face life-altering injuries due to these remnants of war. So it is safe to say that metal detecting could sometimes be highly unsafe. For that reason, drones equipped with metal detectors can come in handy. These drones can scan the ground from above and identify buried metallic objects, such as weapons or explosives.
A metal-detecting drone offers a safe and efficient way to survey large areas quickly and accurately. But it has its limitations. Unless it’s a flat surface – which it rarely is – the drone must fly such that the detectors are always in an ideal orientation.
Solving the Problem
The Autonomous Systems Lab at ETH Zurich is on a mission to solve this problem. The lab aims to develop a unique combination of a detector and a drone with 5 degrees of freedom. It may provide a viable solution to remote land mine detection using careful sensing and localization. For that, they need to develop twisting motors to keep the detector reliably close to the ground.
The most critical and complex part is ensuring the detector’s orientation remains correct to the ground surface to maintain its effectiveness. However, in a conventional drone, this would not be possible. That is because a traditional drone tilts while moving except when going up or down. This negatively affects the detector’s sensors.
The answer? A drone capable of flying without tilting.
Voliro makes the drone used in this ETH Zurich research. The drone is a tri-copter that uses rotating thruster nacelles that move independently of the drone’s body. Voliro is a startup that roots in the Autonomous Systems Lab at ETH Zurich.
Now that the drone is sorted, one needs a control system. The system needs to be able to pilot the drone across a 3D surface that it has never seen before.
All of this while prioritizing the detector’s alignment. To achieve this, the researchers utilize a combination of GPS and inertial measurements from a lidar affixed to the drone. The lidar then provides accurate position and state estimations.
The system then proceeds to autonomously plan and execute a “boustrophedon coverage path” across the area of interest. The term “boustrophedon” describes a technique often used in writing, where alternate lines are reversed and mirrored, such that the writing flows from right to left and then from left to right.
Experiments conducted using metallic targets (non-explosive) indicate that this system performs exceptionally well, even in terrains with obstacles, overhead obstructions, and substantial slopes.
While additional analysis is necessary to determine if this system is helpful for field applications, the fact that the platform employs readily available, off-the-shelf hardware calls for greater optimism.
The Autonomous Systems Lab at ETH Zurich published a research paper titled “Resilient Terrain Navigation with a 5 DOF Metal Detector Drone.” The team will present their research in May at ICRA 2023 in London. Patrick Pfreundschuh, Rik Bähnemann, Tim Kazik, Thomas Mantel, Roland Siegwart, and Olov Andersson co-authored the paper.
In conclusion, metal-detecting drones could prove to be a valuable tool that can go a long way. Thousands upon thousands of people who die or are injured every year could be saved effectively. It all comes down to scientific research and innovation to make sure we make the most out of it.