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

38 just the optimisation of the harness. Moving a function from one resource to another so it doesn’t have to connect to the same ECU can help reduce the complexity of the harness design, but that requires detailed knowledge of system functions and the overall design, which is why the system design tool vendors see the harness as an integral part of the overall design process. The other dimension, particularly for aircraft but also for trucks and cars, is configuration. A car with many different selectable options such as left- or right- hand drive, or different sensor options, quickly creates billions and even trillions of possible choices. For example, in a self-parking vehicle design, the harness for the different options will probably be different, so the modelling of the system for functional modelling or cost is impacted by all these elements. Although the signal links are a key driver, the harness is separate from the signal buses in the electronic systems. Every car and aircraft – even an industrial coffee maker – has a number of digital buses in the ECUs. Overall, say the design tool vendors, the explosion of growth in signals is almost being kept in check by putting more into the digital buses for local connections, but not quite. This means the harnesses are getting bigger as the additional signals need to be shared with other ECUs, and this presents continuing challenges for designers and manufacturers. While bits of wire might be considered old school, there are continuing advances. Large, chunky power leads are moving to aluminium wiring, and while it is lighter it is also harder to make a reliable crimp. Very thin wires are harder to make and fit into connectors, and you have to consider the voltage drop from one end of the wire to the other, as well as selecting the correct wire gauge. But the biggest challenge for tool makers is configuration management. There is a huge range of configurations that are hard to minimise, and every upstream change in the system design requires a change in the harness. This happens on a daily basis, and capturing these changes as part of the overall design process and for maintenance is another big challenge for the tool vendors. This problem of configuration management is worse with autonomous ground vehicles. The ISO 26262 safety standard applies as much to the electrical system as the electronics, and the standard’s process has to demonstrate that the whole system is functionally safe – in that, if one safety- critical component fails then the effect is fully understood and safe, even if the failure is a simple diode in the wire harness or a wire that breaks that is critical to a braking or steering system. ISO 26262 is increasingly important across the automotive industry for failure modes and analysis – if a fuse blows, for example, what’s the impact on the rest of the system? This can impact on the harness design, and these requirements are adding increasing complexity and more demands for safety analysis. So, for example, configuration software now makes it impossible to release a new version of a system until design rule checks have been successful. This moves the problem to the beginning of the design flow and makes it an issue of data integrity that comes from process integrity – the design, manufacture and maintenance – and having tools to help support design for safety. The bigger manufacturers are Tier One automotive and aerospace suppliers that compete on doing more than just making the harness. They will take some level of responsibility for developing the electrical system, not just the physical harness but all the wiring. That means the car or UAV maker will define the connectivity of the individual systems, then a Tier One harness supplier will design and make it. These suppliers will be commissioned to bring perhaps 50 systems together and implement the wiring for that, and from that derive the harness. Connectors As with the harness, the specification of the connectors is driven by the power requirement and the number of signals. Pins sized at 0.3 mm can be used for signals but if the size increases to 0.5 mm it will also be able to run power, which can help to reduce the number of pins and therefore the number of connectors. This then helps with reliability and makes replacement and maintenance easier – if you can push more things through one connector then you can build a simpler harness. Also, designs such as Y connectors can reduce the complexity as well as the cost compared with having two separate connectors. Connector designs are often determined by the harness requirements. A connector with 24 pins can run a twisted-pair cable down an independent line and also has the extra pins to carry power, so when you hook it up you can charge a machine while pulling all the data off. A typical harness design would require up to 48 Summer 2015 | Unmanned Systems Technology Nano-connectors are used at the end of a harness where space is tight, particularly in space systems (Courtesy of Omnetics)