Unmanned Systems Technology 025 | iXblue DriX I Maintenance I UGVs I IDEX 2019 I Planck Aero Shearwater I Sky Power hybrid system I Delph Dynamics RH4 I GCSs I StreetDrone Twizy I Oceanology Americas 2019

78 Focus | Ground control stations Modular design One approach to building a modular GCS is to use a strategy that has been well-established in other industrial sectors. The COM Express standard for example uses a passive carrier board that holds the interfaces to external devices, and a standardised connector to a processor module. That allows different modules to be used for different applications, such as a module with an Intel Core i3 processor for a low-end Windows 10 GCS or a Qualcomm quadcore ARM-based processor for an Android implementation. It also allows the carrier board to be easily changed to add different interfaces to displays, joysticks or data transceivers without having to change the processor board design. Open industry standards such as COM Express have processor modules with long-term support but do not necessarily support all the protocols that might be needed in a GCS design. Custom connectors and protocol specifications might also be necessary to provide the flexibility for a GCS developer to support different aerial, ground or sea vehicles. One argument against this modular approach though is the extra cost that comes from using the carrier board. However, a GCS based around a rugged laptop can cost up to e 6000, while a midrange GCS based on a modular platform can be cost-effective at e 2500, as less custom engineering is needed. That opens up support for a wider range of unmanned systems while still providing several years’ worth of support. One upcoming challenge for midrange GCS designs is how to support 3D visualisation. While basic graphics processing units (GPUs) are being added to rugged laptops, some GCS designs include the ability to add discrete GPU cards to provide more processing power for the display. Battery A key external accessory is the battery subsystem. Some GCS designs based around a rugged laptop use a secondary battery pack that gives a total of 12 hours of operation, and can be replaced while relying on the laptop battery to continue operation. More custom modular designs can have two battery slots and software to support a ‘hot swap’, so that a depleted or damaged battery can be replaced with a charged one while the other continues operating. However, most missions are not expected to take more than 12 hours, so that sets the upper limit for battery supply. Data link An essential part of a GCS system is the video decoder. With a latency from the camera of around 100-120 ms, the decoder has to be fast enough to display the video on the GCS screen in enough time for the user to react. Longer delays in decoding the video make it more difficult for the user to control the craft. This decoder has to be integrated into the GCS display’s software, and achieving that level of latency relies on a detailed understanding of the video encoder on the craft. For example, there are some optimisation parameters such as how to handle lost frames and buffers, as well as handing packet loss. There’s no reason for the decoder to ask for the retransmission of a lost packet of data if it’s too late to visualise the image. It is better to have a bit of noise than no picture, so the decoder can ignore incomplete packets to achieve a responsive video display for the operator. This approach has allowed one GCS developer to demonstrate a UGV being controlled across the length of Denmark via a 4G cellular link with a 120 ms latency, with full HD 1080p video delivered to a 10 in tablet in the GCS. Physical interfaces Connectors are a key element of GCS design, especially when a modular approach is used. Some rugged, high-reliability connectors for example are becoming increasingly popular, but this popularity creates lead times of more than 13 weeks for delivery to GCS developers – and that’s before they get to the customers. For GCS companies aiming to provide a system within eight to 12 weeks, that is a significant design challenge. It means a modular GCS developer will often have to stock quantities of popular components such as connectors. A key challenge for a GCS design is reliability. An operator needs to be confident that it will continue to operate even if different elements fail. Part of that can be achieved using redundancy, April/May 2019 | Unmanned Systems Technology A rugged 10 in Android tablet forms the heart of the Aeronav GCS for unmanned aircraft and ground vehicles (Courtesy of UAV Components)