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33 bringing down a craft with what could be an expensive payload. While many UAVs are not intended for military use, they are often exposed to similar environmental constraints in shock and vibration. That requires robust contacts with sufficient gold plating (usually 50 microns) to ensure a reliable connection. A screw-fit rather than push- fit is also recommended if problems are to be avoided. There is also a trade-off between the reliability, density and type of connector. Circular connectors allow more effective circular sealing rings and so are more common for applications that need the IP67 and IP68 industrial and MIL-DTL military standards on environmental protection. They protect against the ingress of moisture that can cause a short-circuit and a failure, but offer a lower density of connections. Trade-offs also include ease of use. A bayonet connector is quick to mate and release, as is the push-in type, but can potentially work free under acceleration or other stresses and strains. A screw- lock connector, however, provides a more secure connection and sealing against environmental hazards such as salt water or gases, as well as sealing against electromagnetic interference for a metal body connector. A latched connector meanwhile can provide more protection against the environment and unauthorised access, but may need a specialist tool to release it. Rectangular connectors, on the other hand, provide a higher connection density, but designers have to be aware of the risks of the contacts being closer together. That can also limit the current carried by the contact. As more current is carried, the contact heats up. The closer together the contacts are, the quicker the temperature rises and the performance of the contact de-rates. Considerable effort is being applied though to increase the temperature rating up to 175 °C (with some de-rating) for contact pitches down to 1 mm. These challenges of current heating effects can be mitigated by separating power contacts from signal contacts (which is often done by keeping the power connector entirely separate), but that has an impact on the size of the connector, so there is a trade-off between the current-carrying capacity of the connector, the pitch of the contacts and the overall size of the connector. That is what keeps today’s contact pitch at 2 mm down to 1.27 mm, although there is work to reduce that to 1.0 mm. Sometimes there are limited options, however, as the system developer may specify particular standards for connecting sensors or subsystems. Connectors | Focus Circular micro-connectors are designed for board-to-cable interconnect with up to eight contacts and allow space saving as a result of the shape and captive screw fixing (Courtesy of Nicomatic) Unmanned Systems Technology | February/March 2017 One trade-off with connectors is ease of use – a bayonet type is quick to mate and release but can work free under stresses The smallest bayonet lock connector on the market has an 8.6 mm diameter and three-pin crimp contacts supporting AWG 26 cables (Courtesy of Avio Race)