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

36 Focus | Cable harnesses the composite materials that are being used increasingly for the vehicle’s body, reducing the space needed for the harness and simplifying the vehicle’s construction. This can also give the harness more rigidity to prevent it from flexing too much, although the key factor is less weight. The additional complexity required in unmanned system designs plays into the hands of a flexible substrate, as it effectively comes with unlimited capacity since multiple tracks can easily be placed on the substrate. This brings design opportunities for UAVs. For example, if you plug in a different payload you don’t necessarily want to have to rewire the aircraft to accommodate it; a bus arrangement, with power and data and a plug onto the bus could handle that, and the cost in terms of the harness hardware is much reduced by using flex. The flexible substrate makers say there’s no limit to the amount of copper that can be laid down on the substrate to carry the power. The main issue is the cross-section of the copper, and that’s the same for a 16 AWG wire as it is for the flex, so the major benefit comes from the packaging at the lower power, signal end. A 24 AWG wire tends to be the smallest used in an aerospace harness, but for a flexible substrate that’s a large track. One of the main difficulties that the flexible substrate makers point to is that wire harnesses are so omnipresent in every system that it is hard to decide where to focus the substrates. For some designs weight is the key; for others it’s the available space or the flat, planar nature of the flex. This approach also extends the flex out from the electronic control unit (ECU) and allows it to be used between ECUs at subsystem level and even at the system level. Instead of having a flexible link inside the ECU to a connector, then another connector to a flexible harness, the harness can extend directly into the ECU to connect to an individual printed circuit board or module. This offers the opportunity to eliminate many of the connectors but requires a much broader approach to system design and manufacturing. Design tools These new approaches present a challenge to the providers of design tools, which range from simple mechanical modelling tools to system- level design tools that combine the PCB design with the harness design, whether it’s a flexible substrate or a traditional wiring loom. Increasingly, 3D modelling tools are used as well, as the harness becomes more of a component than a connection technology. That means there will always be links between the different levels of design, from the functional and requirements design stages to the physical implementation With autonomous vehicles there’s a lot of data moving around, either within or between them, so there tends to be more high-speed digital networks than in manned vehicles. Ethernet in cars is on the horizon, and as you go through the design tasks there are more and more constraints such as whether high-speed networks can be built in copper, or will optical networks be needed? Optical networks are already used in many modern manned vehicles, and will be used in unmanned versions. This means the optical components in the harness have to be modelled first, as that will put constraints on bend radii because the bending impacts on the performance of the fibre cables. The Media Oriented Systems Transport optical protocol carries data at up to 150 Mbit/s on plastic fibre or copper, and is used by companies such as Audi, BMW and Mercedes-Benz in their driverless vehicles. The increasingly sophisticated data requirements in turn place requirements on the design process and the design tools, and on what is implemented. There are knock-on effects here, in that if you have more sensors and electronics then you also have more signals and more interconnections. That puts challenges on the cost, weight and bulk of a physical wiring harness: in a regular car, a harness can cost several hundred dollars, and there can be ten to 20 of them, so it’s one of the most costly individual components. Each one can also weigh up to 10 kg, and it’s a packaging challenge for installation and repair if one of them goes wrong. The solution to this is wider than Summer 2015 | Unmanned Systems Technology Interconnections in an unmanned system can be designed in different ways, but the design tools need to be able to handle the various technologies and configurations (Courtesy of Mentor Graphics)