Unmanned Systems Technology 024 | Wingcopter 178 l 5G focus l UUVs insight l CES report l Stromkind KAT l Intelligent Energy fuel cell l Earthsense TerraSentia l Connectors focus l Advanced Engineering report

84 be too bulky to fit among dense PCB connections, and the excessive use of fasteners can add significant weight to UAVs, making them unsuitable for unmanned HALE aircraft and other designs that have weight saving as a priority. Other locking techniques continue to be developed. One of the newest (patent pending) configurations involves a series of spring-loaded balls around the inside of the receptacle, which squeeze outwards during mating before clipping back into place. A metallic ring behind the balls provides the locking pressure to keep the plug in place. Magnetic connectors are also being developed, and these can offer quick and easy mating. However, surrounding systems can be subject to interference as a result of the magnetic flux, and if metallic debris is attracted between the plug and receptacle, the quality of the mate – and thus the connection – drops. Strong vibrations near UAV and UGV engines can also cause a resonance between the male and female faces of magnetic connectors, which reduces the signal delivery rate. Magnetic connectors might therefore not be ideal for unmanned systems that have dense electronics bays or are prone to significant vibration. D-sub and micro-D D-subminiature (D-sub) rectangular connectors have a history of use in large unmanned vehicles with high power needs, such as in their drive-motor sections, or for actuators for extending large antenna arrays or control surfaces with major load-bearing requirements. The design of the D-sub can feature pitches as small as 1.9 mm, allowing for connections with standardised wire sizes up to 22 AWG, or 0.644 mm in diameter. That can allow 7.5 A per contact, or as much as 10 A for short duty cycles. However, the micro-D has overtaken the D-sub in unmanned systems by some margin, owing to the drive to optimise the size and weight of components. Micro-D is designed to meet (and are synonymous with) the MIL-DTL-83513 standard for applications that require stringent weight-saving, miniaturisation or signal transmission integrity. The popularity of micro-D has driven the development of significant customisability. Some suppliers can now offer 83513 connectors with up to 120 contacts across four rows, with pitches keeping to the 1.27 mm minimum typical of the 83513 standard. The manufacturing cost of micro-D connectors rises sharply with specialised or customised designs such as these, because unique or limited tooling must be used or developed from scratch, to mould the connector’s complex and precise dimensions. However, critical space can be saved by configuring for one 120-pin connector fastened with two screws, rather than three 40-pin connectors needing space either side for two screws each. That can be particularly important for motherboards and other circuits that push the limits of high density and space-saving requirements, as in self- driving road vehicles and other vehicular machine learning systems. To date, the micro-D’s wire sizing – 24 to 32 AWG, or from 0.511 mm to 0.202 mm – retains marked benefits for high signal performance (3 A in standard use, higher for short bursts) in lightweight, small circuitry. Its standardisation makes it available in vast quantities across a range of applications, with standard mounting patterns installed in most PCB design software. For even further SWaP optimisation, the MIL-DTL-32139, or nano-D, is designed for a 0.635 mm pitch, 30 to 34 AWG (0.255 mm to 0.16 mm diameter) wiring, and 1 A standard current flow. The nano- D’s required shock and vibration testing renders this connector suitable for UGVs in rugged terrain or UAVs taking off and landing on runways. Nano-D Nano-D connectors have become particularly viable for unmanned vehicles as the SWaP optimisation of UAV components has led to lower current and voltage requirements, with many payloads, detectors and navigation systems increasingly requiring voltages as low as 15 V. This connector type is naturally suited to tight space requirements in small avionics bays, and has also been configured to handle a wide range of signals, from analogue to high-speed digital formats including USB 3.1, HDMI and 10 Gbyte Ethernet. Nano-D connectors are particularly important in UAVs carrying payloads February/March 2019 | Unmanned Systems Technology Focus | Connectors Both micro-D and nano-D connectors are increasingly customised to carry contacts for power, signal and RF simultaneously (Courtesy of Positronic)