Unmanned Systems Technology 003 | UAV Solutions Talon 120 | Cable harnesses | Austro Engine AE50R and AE300 | Autonomous mining | AUVSI 2015 show report | Transponders | Space systems

33 highlights the separation between the power and comms functions. To build a harness, cables of different thicknesses can be woven together into a ribbon, with the thicker cables delivering power and the thinner cables carrying signals. The thousands of cables required in a vehicle constitute considerable weight and cost, however, and while some harness makers are starting to use aluminium rather than copper to reduce the weight, there is also a move to adopting different approaches for connecting sensor units (see below). Some unmanned systems are able to challenge the existing design methodologies. For example, having solar panels on the wings and body of a UAV allows power to be provided closer to the sensors and actuators. This removes the need for distributed power cabling around the craft, potentially reducing the complexity and weight of the harness. However, the trade-off is that more power management devices have to be distributed around the craft. This highlights the need for the harness to be an integral part of the design of the system, and for different architectures to be assessed to provide the optimum design with minimum weight. Cabling There are various ways to build a conventional harness, ranging from bundling a set of wires together to weaving them together. Cables have been woven into ribbons for more than 45 years, but like everything else in the modern world the harness has evolved over that time. At the moment, developers tend to build a system and hang a harness on it afterwards; going forward though, harness makers will need to provide the interconnectivity wherever it is needed throughout the unmanned system. This means that the design and project managers can rethink wiring systems away from conventional approaches and integrate new methods (see below) into their products that allow them to build lighter systems with higher performance. Very often the conventional harnesses limit the design of an unmanned craft. There are existing specifications and conventions for the interconnections that have been used for many years, and it takes a brave engineer to adopt a new way of implementing these connections instead of something they’ve used for 20 years. Now though, using wires as small as 44 AWG allows a ribbon cable only 9.5 mm wide to be built with 50 twisted pairs which provides substantial signal connectivity. Many spacecraft have these ribbons on either the flight harnesses or in the instrumentation packages and experiments. A newer approach is to put these ribbons inside a jacket or shell. One application of this is to provide power for de-icing the rotor blades of a helicopter, and essentially these aren’t a harness any more, but shaped components accurate to +/- 1.00 mm with clamps and pads built in and made from a 3D model. This application is one of the harshest environments an interconnection system can work in. The choice of shell or jacket materials depends on the application, and typical materials include polyurethane and epoxy. It is possible to put 50 conductors in a ribbon within a structure that’s 1 mm thick and 19 mm wide; these are still built as an add-on harness, but with UAVs in particular the aim would be to lay the ribbons into the airframe structure. Using 44 AWG wire to carry signals in the Cable harnesses | Focus Harness designs have traditionally used copper wires but optical fibres and even wireless links can be used. Each type though has its challenges Unmanned Systems Technology | Summer 2015 Weaving cables into a ribbon for a harness (Courtesy of Tekdata)