Inside Unmanned Systems

OCT-NOV 2017

Inside Unmanned Systems provides actionable business intelligence to decision-makers and influencers operating within the global UAS community. Features include analysis of key technologies, policy/regulatory developments and new product design.

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MARINE NEW APPLICATIONS 62 unmanned systems inside   October/November 2017 "Given how much we take fast WiFi and GPS for granted, which also enabled a quantum leap in mobile robotics, it is easy to forget how much harder things get when these two are gone." Hydromea's specialty is making robots that can "cooperate with each other and commu- nicate with each other with acoustics," Schill said. "The robots send each other acoustic pulses they can use to report to each other. They can also measure how long it takes for them to get these pulses so they can coopera- tively get an idea of where they are in relation to each other in the swarm. The robot that had the last GPS measurement can share that in- formation so the swarm as a whole can esti- mate where it is. Our algorithms also calculate when the robots send data and when they need to be quiet." Acoustic communication is not well-suited for continuous use by many robots, as they can begin to interfere with each other. As such, Hydromea only uses acoustics for sparse long- range signaling of very small amounts of data. "For short-range communications over 20 or 30 meters, we've looked into very low-frequen- cy radio waves," Schill said. "We've also looked into optical communications using visual light, which can communicate much more data, but only over a couple of meters." Vertex Hydromea's autonomous underwater vehi- cle (AUV), known as Vertex, "is meant to be deployed in groups of five to 10," Bahr said. "These vehicles either work independently to map a larger area in parallel or share informa- tion to autonomously track a feature such as a plume." The Vertex is about 70 centimeters long and 7 kilograms in weight. "The AUV uses re- chargeable lithium-ion batteries," Bahr noted. "They last for about eight hours on normal cruising speed—max depth 300 meters, max speed 1.5 meters per second." The Vertex uses the EXO2 sensor system from YSI in Yellow Springs, Ohio, which can be configured with up to seven different physi- cal, chemical and biological sensors. "These sensors can measure temperature, depth, con- ductivity, oxygen, pH, various algae, turbidity, fecal matter, ammonium, nitrates, chlorides," Bahr said. "For a typical mission, the bulk of the data is collected by directly off loading it from the vehicle via cable." The compact thrusters the researchers devel- oped for Hydromea lack central hubs in their propellers. Instead, the blades of each propel- ler project inward from the rim, and the entire rim spins. The absence of a central shaft greatly reduces the risk of entanglement with floating debris, the researchers said. Bahr noted that one problem with develop- ing Vertex was how unforgiving water is. "If your robot is not 100 percent waterproof, you lose it—and it's gone for good if the water is deeper than a few tens of meters," he said. "Also, if you want to keep your vehicle this small, you need to build everything from scratch, and you need to go component hunt- ing," Bahr said. "For example, a typical un- derwater connection is already half as big as our AUV, so finding small yet still suitable pressure-proof connectors is challenging. You overcome these problems simply by continuing to work at them, which usually means that it takes longer than you thought." Tracking Pollution Hydromea has performed field tests of its robot swarms in indoor tanks; in Lake Onego in Russia; and Lake Cadagno in Switzerland. "Our AU V is fully autonomous—it can either be preprogrammed with a series of way points, or the path can be controlled by pollution data," Bahr said. "We recently did an experiment where we wanted to take measurements in a very thin 1-meter bacte- rial layer at an unknown depth, so we pre- programmed special way points that only "THERE'S NO CENTRAL CONTROLLER, no coordinator robot. If any of the robots have to leave or get lost, that will not affect the rest of the group." Felix Schill, co-founder, Hydromea

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