Unmanned Systems Technology 024 | Wingcopter 178 l 5G focus l UUVs insight l CES report l Stromkind KAT l Intelligent Energy fuel cell l Earthsense TerraSentia l Connectors focus l Advanced Engineering report

60 Digest | Stromkind KAT series shape of the screw, which is built using additive manufacturing (3D printing). Control system Using jets of water for the propulsion also allows different approaches to the control systems. Jets can be directed in different directions, including sideways and even downwards to provide more stability. This required the development of a vector- based control system that is very different from mainstream USV control systems. “The problem is there are a lot of parts, with a motor drive, controller, batteries, battery management system, electronics and cooling – it’s a complex system,” Desch says. “So we put the motor into the flow to cool it – that’s one major aspect. Then we put the electronics in the box with the motor to cool it as well.” That has the added advantage of reducing the length of the three-phase cabling that connects the electronics to the motor, which can have a lot of inductance that increases losses and reduces the motor’s efficiency. The team worked on the hydrodynamics to produce a very laminar flow of water coming out of the tube. That comes from the design of an exponential screw that is shaped to get the most power into the water and provide the maximum thrust for its diameter and length. It is 3D-printed in aluminium. Applications The thruster technology has been coupled with the catamaran design to provide a range of sizes, from 1.5 m to 10 m long, for applications such as carrying full-sized shipping containers, firefighting and plastic waste collection. The craft range from the KAT-150 to the KAT-500, and carry various sensors for the autonomous operation. There is a trade-off between the size of platform, the size and power of the thruster, the type and power consumption of the sensors for a particular application and the size, weight and capacity of the battery pack. “From the product side we came up with the smaller one, the KAT-150, but found that the market needed bigger equipment,” says Desch. Using the 1.5 m KAT-150, the team tested the propulsion, motor controllers, electronics and energy harvesting via solar panels, although with the 150 there wasn’t the space for enough solar panels to generate the required power. They have now begun developing a 3 m version, the KAT-300, which was the minimum size that can be solar-powered. A solar panel of 1 m 2 generates 200- 250 W to charge the batteries. “The concept is that you have fully charged batteries and you top up with solar power during the day,” Desch says. “That gives you 24/7 operation, and even in bad weather you easily get 5 kW over a day with the solar panels.” Once Stromkind had all these things in place, potential customers wanted to use it in higher waves in the open sea, but 3 m is too small for applications in the open sea, says Desch, so they started working on the 5 m-long KAT-500. Most customers in the big shipbuilding industries in Asia and India then started asking for even bigger craft to carry cargo, so the question was whether to develop a 7.5 m KAT-750 or a K1, a 10 m platform, around the more powerful thrusters. Stromkind started out looking at the platform for collecting waste from water, whether it’s oil on the surface or plastic waste. It soon became apparent though that tweaks to the platform design could open up other applications. The 10 m version would also have benefits for ocean cleaning applications, because present systems are not working as well as expected at clearing plastic waste, as it gets snarled up in the drive and propellers of conventional craft, says Desch. “We started with propellers, and when you start collecting things in the water they can be a problem. They are not very efficient, and once its stuck the mission is over, and that’s a challenge for autonomous systems. It’s also a problem in very shallow water with vegetation,” he says. The 7.5 and 10 m platforms would have more space for solar panels to drive the pump motor and store the collected plastic. This gives a longer mission February/March 2019 | Unmanned Systems Technology The 1.5 m-long version of the KAT has been tested in open water