Cable assemblies and wiring harnesses connect different subsystems of UAVs and robotic vehicles together, including batteries, sensors, autopilots, propulsion systems and flight controls. They route power, signals and data from one place to another, and are designed to save space and weight compared to separate cables.
In addition to meeting size and weight constraints, the design of cable assemblies may have to take a variety of other factors into consideration. They may have to be integrated into UAV airframes and vehicle chassis with complex routing requirements, and may need to flex through significant angles without wear. Outer cable protection may also have to deal with the fact that shock and vibration can cause cables to rub against sharp corners and other surfaces, causing structural weaknesses.
Cable assemblies for unmanned systems may need to be resistant to a range of substances, such as gasoline, diesel and oil. IP (ingress protection) ratings for moisture and immersion resistance may be important, especially for maritime and submarine systems such as USVs (unmanned surface vessels), ROVs (remotely operated vehicles) and AUVs (autonomous underwater vehicles).
Cable assemblies are typically constructed with one or more conducting wires or optical fibres at the centre, with insulation around each wire or groups of wires. Copper is typically used for conductor wires, due to its power-to-volume ratio, corrosion resistance, and relatively low cost. Conducting wires may be a single solid core or multiple strands twisted together.
Cable insulation can be made from a variety of materials, each with advantages and disadvantages:
Silicone rubber is highly flexible, temperature-resistant and allows a wide bend radius, but is prone to outgassing (release of chemicals originating from the curing process).
Polyethylene has a lower temperature resistance but possesses dielectric properties that make it useful for RF cabling.
Fluorinated ethylene propylene has high resistance to extreme temperatures, fire and chemicals, and can also be manufactured with desirable dielectric properties for RF applications.
Many UAVs and unmanned systems contain a large amount of electronics and components that can potentially emit radio-frequency (RF) and electromagnetic radiation. Cable harnesses may thus have to be protected against EMI (electromagnetic interference) to stop them from acting as antennas and picking up unwanted noise. This can be done by using sufficient shielding and grounding. Cable harnesses may have to conform to specific EMI requirements such as military specifications.
Custom wiring solutions manufacturers can create cable assemblies for everything from small battery interconnects to complete UAS command and control systems, with a wide range of insulation, conductor and connector options. They can test cables to ensure that they will survive demanding environments and thousands of flight hours without failure, using methods such as high-voltage testing, insertion loss testing and pull force testing.