Unmanned Systems Technology 001 | UAV Factory Penguin C | Real-time operating systems | Hirth S1218 two-stroke twin | Base stations | ASV C-Enduro | Composites | Datacomms

56 Dossier | The ASV C-Enduro environmentally sealed to IP67 enclosure rating (an international standard that recognises a battery totally protected against dust and the effect of immersion in water to a depth of 1 m). Each pack is bolted into the hull and communicates with the other and the CAN ECU, allowing them to be operated as a single unit. Each pack contains battery cells, a battery management system (BMS), a battery fuel gauge (BFG) and a safety fuse. The cells are of the lithium-ion polymer (soft) pouch type since, says Shaw, “This type provides the highest energy density you can get. These lithium-ion cells are also good for power, so we use them for automotive applications as well.” It is a characteristic of lithium-ion batteries that supposedly identical cells, even from the same production batch, do not have identical capacities or charge/ discharge rates. Moreover, the key to rapid charging and discharging is to protect the cells, which are all too easily destroyed in the process. Shaw explains that they need a specific charging method, which involves how the current is moved around between them in the light of prevailing temperature and other parameters, so that they are properly balanced. “The routing of the high-current conductors in the internal circuitry is crucial,” notes Shaw. “It is how the individual cells are mounted and how they are electrically connected; it is about how we integrate everything into a pack. That is where some of our unique intellectual property lies.” On top of that, Hyperdrive’s BMS controls the voltage of each individual cell to keep them all identical at all times, which maximises the available capacity of the pack. According to Shaw, this balancing permits the fastest charging and the highest energy density of any lithium-ion control system on the market. “Our BMS exploits very sophisticated software and has functionality that is unique,” he says. Nevertheless, the BMS doesn’t indicate the charge state of each cell, or even whether they are charging or discharging. It is a quirk of lithium that the output voltage does not indicate the exact state of charge of the battery, and this is where Hyperdrive’s BFG comes in. In essence, it measures what goes into the unit and what comes out, and from that calculates what is still inside. Shaw explains that the BFG takes clues from measurements of the input and output voltages, and over time learns from those to help assess the capacity of the pack, which will degrade over time. The BFG accounts for the effect of cell ageing, via a combination of theoretical modelling and actual measurement, and the data from the BFG can be accessed in real time via telemetry. In the C-Enduro the BFG data is used in conjunction with the BMS as a key control input. The wind turbine The wind turbine is not designed to work in conjunction with a shroud (unlike for example the ‘accelerator’ type, which is a spin-off from Formula One diffuser development). More conventional, it is an off-the-shelf three-blade upward generator. Having a 1.76 m diameter area swept by its carbon fibre blades it is as large as is permitted by the anti-capsize hooped superstructure surrounding it. An integral rudder alters its angle of attack according to wind direction. Its cast- aluminium body contains a stock, hub- mounted permanent-magnet electrical machine, which provides a three-phase output. Once wind speed reaches 30 kn, that output is more than 500 W, rising to a maximum of around 650 W and with the turbine having a survivable wind speed of over 130 kn. As per standard, passive blade pitch control allows for continuing operation in high winds – in essence, counterweights at the hub alter the pitch as a function of November 2014 | Unmanned Systems Technology Close-up of the Hyperdrive battery pack circuitry The C-Enduro can exploit wind power to recharge its batteries via its wind turbine