Sonar images generated in real time
“We program in the route beforehand, and then ThunderFish Alpha autonomously scans the desired area of the lake bed using high-tech sonar equipment,” says Helge Renkewitz, a researcher at Fraunhofer AST, a branch of Fraunhofer IOSB in Ilmenau, Germany. The scientist and his colleagues were on location for the search. Based on acoustic echoes, ThunderFish Alpha generates sonar images in real time, which can then be analyzed by the experts directly after the dive. Image data can be transferred wirelessly, and give precise indications of potential item locations.
Up to the end of September, the team was on the hunt. “During this period, ThunderFish detected 400 objects, 100 were already examined. Two of them proved to be the lost Arrow models that are scheduled for salvage before the end of the year,” says Renkewitz. Meanwhile, the search has had to be put on hold because of the weather; it is to be continued from June to September 2018. All in all, ThunderFish has a surface area of 64 square kilometers to scan.
The AUV is powered by eight batteries, each weighing 15 kilograms apiece. A quick-release mechanism allows for these to be exchanged in a few minutes. A single battery charge is enough for 20 hours of exploration, and the software for the clever battery management system was developed in house at the Fraunhofer Institute for Silicon Technology ISIT in Itzehoe, Germany. The AUV also carries navigation sensors, two sonar modules, propulsion and steering units, communication modules, the software management system, data storage devices and a CAN-BUS system. This is a streamlined cable system that makes it possible to attach all the control units and electric motors. It offers certain advantages: for one, minimizing the amount of cables and connections minimizes malfunctions. What’s more, attaching new modules, sensors or test devices to the standardized CAN-BUS is a quick and easy process. “The modularity of our AUV was one of the reasons Kraken chose DEDAVE,” says Renkewitz.
Five-year collaboration agreement with Canadian partner
As part of a five-year research agreement with Kraken Robotics Inc., Fraunhofer IOSB will be consulting for the company and helping it develop new versions of the AUV. As the software has not been licensed out, developing it will remain Fraunhofer’s exclusive responsibility. The licensing agreement stipulates that Kraken gains exclusive rights only once the AUV surpasses a weight of 750 kilos. That is to say, if Fraunhofer designs new variants with other sensors that result in a lesser weight, then Fraunhofer is free to offer those modified vehicles to other customers as well.