Unmanned Systems Technology 023 I Milrem Multiscope I Wireless charging I Logistics insight I InterGeo, CUAV London & USA show reports I VideoRay Defender I OS Engines GR400U-FI I Ultrabeam Hydrographic Ultra-2 I IMUs

36 Focus | Wireless charging voltage/constant current approach. That delivers a fixed amount of current until it reaches a set voltage, when the current decreases to top it off, avoiding the need for complex comms between the transmitter and receiver. The coupling works at 6.78 MHz, a different frequency from other approaches. Unlike some other systems, the charger is programmable and can be controlled via a user interface or a wireless 2.4 GHz data link. With the cart or UGV at the charging station, the programmability allows the charger to ramp up the current to the maximum rate for that battery for operational charging, or down for overnight charging. The system is designed to support multiple vehicles at a time, something that is impossible when the receiver coil has to be aligned closely with the transmitter. This allows several UAVs to share a landing pad or lots of UGVs to share a charging point, even if they have different batteries. The details of the specific battery on a UAV or UGV is included in the data handshake between the receiver and the transmitter units. One system has been deployed in a wave energy test centre. It consists of a transmitter plate connected to a wave energy generator and a battery that acts as a charger for when a UUV swims up to recharge. The wave energy generator had initially been connected to the local electricity grid, but the focus now is on supplying power direct to UUVs via charging points. Future developments will look at extending the range of the system from 5 cm to a metre or more. Capacitive systems use an electric rather than magnetic field for coupling the transmitter to the receiver, and can provide a longer range. These are of growing interest for UAV applications, although the limiting factor for deploying such charging systems is the regulatory prohibition on line-of-sight operation of UAVs. The use case for wireless charging is that it allows a UAV to travel over larger distances, recharging autonomously along the way. If it cannot operate beyond visual line of sight there is less need for a wireless charging system. However, that restriction is likely to be lifted by regulators around the world in the next few years, opening up more opportunities for applications such as monitoring pipelines. Using wireless charging would open up different models of deployment, and that has an impact on a system’s design. If landing/charging pads are to be placed every few kilometres along a pipeline then they need to be low cost, and the power receiver in the UAV has to be more complex to compensate for the low-cost transmitter. However, having a pad to land on may be impractical for other monitoring applications such as pylons. Here, a transmitter that doesn’t require a landing pad could be used, recharging the battery of the UAV while it is still in flight. Another use case would be for surveillance. A fleet of UAVs could be used to autonomously monitor a perimeter, for example, returning to a charging pad at regular intervals. A capacitive system by contrast uses simple receiver plates on a UAV, which could be just a section of foil coating its legs. That gives a significant weight advantage over magnetic systems, and does not suffer from their heating December/January 2019 | Unmanned Systems Technology A sprung contact system allows a UAV to recharge without having to plug in wires (Courtesy of Skysense) Capacitive resonant charging for UAVs (Courtesy of Solace Power)