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

68 flexibility in where they fix the system onto their airframe. “For the prototype flights, we needed only two standard M3 screws to secure the module to the M100’s undercarriage, with the electrical connectors and hydrogen connector as the only other protruding parts,” Kelly says. “For more dynamic systems, such as VTOL-transition UAVs or fast UGVs, you could use more fasteners or screw it top and bottom.” The entire fuel cell module is designed to keep the centre of gravity (CoG) in the middle of the system, between all the mounting points, and with the weight allocated symmetrically lengthways as well as widthways to aid installation. As Kelly explains, “If you want to put a payload in a particular place, and make sure your CoG is right, you can just move the fuel cell module forwards or back accordingly to balance your craft.” The fuel tank is easier still to place, as the difference in weight between a full one and an empty one is negligible. A 1.5 litre hydrogen cylinder filled to capacity at 300 bar will only be 28 g heavier than an empty one. The fuel cell system is also designed to be used modularly. If a UAV needs a higher power supply then two or more systems can be connected together. Taking two 800 W units and combining them with a parallel connection will provide 1600 W on the 25 V DC output. More typically, an end-user could choose to connect them in series, and get 1600 W at 48-50 V, similar to a 12S battery system. Most of the fuel cell’s development has focused on removing the need for UAV manufacturers or operators to have a fuel cell engineer onsite to use it, with CE and FCC certification and single-point fault tolerance as additional goals. To initialise the energy production the user presses a button on the side. This opens the solenoid valve inside the pressure regulator and the inlet valve in the fuel cell housing, so that hydrogen gas can flow onto the anode layers of the cells. The gas passes through each cell’s diffusion layer and onto the catalysed electrode, to produce a voltage with air present at the cathode. It also instructs the hybrid battery to provide initial power for the power electronics section. The control unit then conducts various safety and functional checks. These include assessing that the voltage is correct, that all the cells are operating within healthy parameters, that the battery is charged and that there is enough pressure in the tank. Once the module has been initialised and these start-up checks have been performed, the operator presses the same button again to activate the voltage output. Oxygen and cooling Although the 800 W fuel cell has two air fans, it does not draw double the air, as only an extra 150 W of heat is generated. February/March 2019 | Unmanned Systems Technology A brushless electric UAV motor from T-Motor is used for drawing air into the fuel cell for cooling and for the cathode