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

34 Focus | Cable harnesses milliamp range for the transponders and sensors, we can get right down to the smallest implementation with miniature coaxial and quad connectors. However, power is power, and a high-power brushless motor draws a lot of current, meaning you need a lot of copper, so harness designs are flexible enough to contain larger current-carrying wires alongside fine signal wires in a weave that is 8-10 mm in diameter. This allows a large conductor to run alongside smaller cables and still keep weight and size down. A key advantage for harness makers is that the UAV market is not constrained by conventional design methodologies. For aerospace in general the MIL-STD standards apply in military designs, and there are similar standards such as IPC-WHMA-A-620, but these military standards do not necessarily apply for commercial UAVs. Increasingly, electrical wiring and interconnection systems are not defined as a commodity component but recognised as a complex, safety- critical system, and so safety standards will be more important to the harness design and manufacturing process. This is already the case with the ISO 26262 safety standard that applies to traditional as well as driverless vehicles, for example. While this ability to experiment with new approaches to interconnection can be extended to new technologies such as wireless, there is concern that such systems could be compromised by accidental or deliberate interference. Safety-critical systems signals running on shielded assemblies are more secure, which increases the need for coaxial and shielded signals to be included in the same ribbon. The cabling does not always consist solely of copper and aluminium though: in autonomous space systems in particular, the intense cold makes these metals brittle and prone to fracture, so specialist alloy conductors are often used in such applications. The connections can become superconducting at very low temperatures, reducing power losses but making the harness design even more complex. However, copper is most commonly used for UAV applications, as it’s readily available, easy to terminate and at the small sizes being used is regarded as so lightweight that lighter materials are not economically viable. Flexible substrates Nevertheless, one new approach to reducing weight is to use a flexible printed circuit substrate, or flex, that carries power as well as data. In the past, using flex has been limited by the weight of the substrate and the length of track that could be produced, but it is now possible to make flexible and lightweight substrates from a single roll of material in tracks of up to 50 m. This allows the connectivity to be designed in the same way as a printed circuit board, with the same tools. Also, the width of the tracks, and the gap between the tracks, can be varied according to the current and signal requirements. This reduces the weight of the harness, as the current is carried in the skin of the metal track. Another advantage comes from the ability to integrate the track into Summer 2015 | Unmanned Systems Technology A flexible substrate developed as part of the EU CleanSky research programme can carry signals and power for over 50 m, replacing complex, heavy cable harnesses (Courtesy of Trackwise)