95 determined in-house and presented to the harness maker, as more information will naturally mean a more optimised product. For instance, a cable designed for running into a gimbal could consist of a silicone rubber jacket for high flexibility, and the wiring inside could have extremely high stranding. Rather than using something like a conventional 7 or 19-strand copper wire, the high-density data outputs and highspeed and fidelity control inputs typical of modern UAV gimbals could mean using wire in excess of 40 very fine strands. The more strands in the wire , the higher its flexibility, life expectancy (particularly against scratches and nicks), and heat dissipation. On top of that, speciality wires such as tinsel wire are available that can provide very high flexibility but at the cost of low current throughput. Also, safety-critical niche requirements must be addressed early on. Some vehicle OEMs require harnesses and other components to be made without magnetic materials if, say, a magnetometer or similarly sensitive instrument is nearby and the vehicle designer wants to avoid sources of interference. In that case, connectors with nickel plating for instance would be off limits, as would any shielding or braiding. Some customers choose to approach cable harness manufacturers with source control drawings, which will typically define the range of tests they need across conductivity, vibration and so on. From reviewing that information, a cable harness maker can produce a list of what does and does not need to be discussed further to pin down material and engineering requirements, as well as potential substitutes, as those discussions progressively unearth which wire types, manufacturing approaches, or jacket materials for instance are unacceptable for the use case. Once the ideal components and parameters of the harness are defined, the cable producer can start modelling the ideal harness in CAD (not with FEA, as there are too many variables to accurately simulate lifespan or performance), to produce a drawing that the customer can check and send back with requests for iteration or sign-off. Manufacturing can then begin. Manufacturing and QC Production of a cable harness typically begins with cutting multiple single wires to the desired length, after which the ends of the wires are stripped of their protective coatings so that the exposed copper (or other core material) can be attached to connector pins. The wires are then bound or twisted together depending on the end-user’s preferences. Twisted pairs or higher quantities of wire being weaved together is desirable from an EMC standpoint as it reduces EM radiation from the weave and increases rejection of external EMI, although it does drive up the cost of cable harnesses owing to the labourintensive nature of the weaving process. Naturally, twisted or weaved wires are increasingly popular in the uncrewed world given the higher quantities of embedded computers, modems, sensors and other electronics and sources of EMI inside vehicle hulls. After that, the wire assembly can be fitted into its protective jacket, which can encompass various materials and layers depending on the application and integration case. Aluminium shielding for instance can provide further EMI absorption, and a wide range of plastics are available for different temperature, chemical and physical hazards. After these main jackets, other components such as abrasion-resistant sleeves can be fitted over key sections of the harness to counter potential threats to its integrity in the vehicle. Lastly, the exposed conductor is attached – by crimping or soldering – to its connector, each wire and its pin corresponding to a function for the harness. Adhesive and other bonding options are available for securing outer cable jackets to connector shells, with stronger adhesives used in cases such as military uncrewed systems, where technicians in a rush could grasp and pull cables with more strength and at angles than are not ideal for safe de-mating, creating a risk of wrenching cable and connector apart. Most of these steps in the manufacturing process are still carried out manually. Procedures such as weaving, or inserting and routing wires through sleeves, are cumbersome for a machine to execute. Cable harnesses | Focus Uncrewed Systems Technology | October/November 2023 Most cable manufacturing must be done by hand, from weaving wires together to stripping and crimping of conductors to pins (Courtesy of Harwin)
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