Unmanned Systems Technology 038 l Skyeton Raybird-3 l Data storage l Sea-Kit X-Class USV l USVs insight l Spectronik PEM fuel cells l Blue White Robotics UVIO l Antennas l AUVSI Xponential Virtual 2021 report

68 Dossier | Spectronik PEM fuel cells toggling up or down too aggressively. “A small hybrid battery or even a supercapacitor is more than enough for providing those instantaneous jumps in power while the cell stack’s power output catches up or for absorbing the excess power during deceleration. We’ve had good results with Maxwell supercapacitors, which we can supply as standard with our closed-cathode products.” Jap further notes that end-users could also benefit from this arrangement by using the hybrid supercapacitor or battery for energy regeneration (from wheels or rotors during braking). “In many UAV fuel cell arrangements, the hybrid battery needs to be large and heavy enough to store sufficient energy for sustained, stable propulsion as well as provide power to the control systems amid periodic current pulsing, and also because it often provides the power boost needed for take-off while the fuel cell is initialising. “As we don’t use current pulsing, our cell’s electrical supply is self-sustaining, so the cell itself never needs to take any power from the hybrid battery – users can therefore right-size this aspect for their application. For instance, a supercapacitor could instead be used for handling the higher transient loads much better than a battery, and without losing lifespan or having any of the other safety issues that lithium batteries can come with.” To ensure that such alerts and performance telemetry are available to the end-user independently of (or redundantly alongside) their own UAV’s data links, the standard Protium cell also comes with an integrated radio modem. The model used is an RFD 868x Modem BARE from RFDesign, which has a 10 km range and a data link bandwidth of 500 kbit/s (up to a maximum of 750 kbit/s if the user increases the output power above standard limits). It transmits over the 868-869 MHz band with a typical output of 1 W (+30 dBm) and AED hardware-accelerated encryption for users’ data security, along with electroshock-discharge protection and filtering on all I/Os. “That means users can accurately track and record voltage, power, temperature, remaining fuel and so on to carry out smart analytics on these at their control station if they wish,” Jap adds. Conclusion The company has been supplying open- cathode cells to the industry for a few years now, and plans to continue offering them as well as its closed-cathode types for long-endurance electric UAVs, in applications including offshore asset inspections, persistent urban survey and search & rescue operations. These plans include integrating its cells into a new version of the Phoenix UAV from Thunder Tiger Robotix, which will be capable of 180 minutes of flight with a 2 kg payload, and which is anticipated for release next year. Continued r&d into ways of further enhancing the manufacturability of its systems is also anticipated, to ensure mass production can be achieved as commercial and civil UAV operations become part of daily life in cities worldwide. June/July 2021 | Unmanned Systems Technology Protium Aerospace fuel cells PEM fuel cells Hydrogen gas, dry, 99.999% purity Closed cathode Air-cooled TBO: 1000 hours Protium-1000 Dimensions: 322 x 290 x 154 mm Weight: 3.03 kg Operating voltage: 18-27 V DC Operating current: 55.5 A Maximum current: 66.6 A Operating power output: 1 kW Maximum power output: 1.2 kW Protium-1500 Dimensions: 434 x 290 x 154 mm Weight: 4.22 kg Operating voltage: 27-41 V DC Operating current: 55.5 A Maximum current: 66.6 A Operating power output: 1.5 kW Maximum power output: 1.8 kW Protium-2000 Dimensions: 492 x 290 x 154 mm Weight: 5.27 kg Operating voltage: 36-54 V DC Operating current: 55.5 A Maximum current: 66.6 A Operating power output: 2 kW Maximum power output: 2.4 kW Protium-2500 Dimensions: 548 x 290 x 154 mm Weight: 5.84 kg Operating voltage: 45-68 V DC Operating current: 55.5 A Maximum current: 66.6 A Operating power output: 2.5 kW Maximum power output: 3 kW Some key suppliers Membrane electrode assemblies: Gore Gas diffusion layer: SGL Carbon Sigracet Electro-valves: The Lee Company Oxidant blower: Micronel Cooling fan: Delta Electronics Gas ports: Swagelok Metal cooling fin: Robinson Fin Machines Cell voltage monitoring module: Infineon DC-DC converter: Synqor Supercapacitors: Maxwell Fuel cell controller: Microchip Technologies Radio modem: RFDesign UAV development partner: Thunder Tiger Robotix Specifications