100 Focus | Servos that produce more torque than their control surfaces and linkages can withstand, thinking that a stronger servo is a safer one. For such cases, deploying duplex actuators with intelligent, embedded software modules written to electronically limit torque outputs can be vital. The reasons are to prevent accidental damage to flaps and ailerons, and to disengage the limiter function when one lane fails so that the single lane is free to generate its maximum torque, and make up for the torque now missing from the failed motor and geartrain. Smaller servos In the past few years, there has been a rise in demand for small but robust servos, capable of up to 2000 hours between failures, with interfaces such as CAN or RS-485 to provide feedback on parameters such as current and temperature. That helps professional UAV operators across logistics and defence to minimise their maintenance costs. That trend has continued, and there are now some servos weighing 30-60 g that are capable of CAN comms and many thousands of hours of operation, not to mention significant torque and power efficiency for their sizes. Naturally, these capabilities stem from the use of highend motors, gears, bearings and cases. Such servos have also proliferated for the underwater market, with UUV integrators having clear options for oilfilled, pressure-tolerant actuators capable of a variety of depths, sometimes several thousand metres below sea level. However, with the rise of hobbyist aircraft and UAV manufacturers moving into the semi-professional UAV space for smaller business providing services such as agricultural surveys or bridge inspections, servo manufacturers are finding ways to meet the low price points these new manufacturers need without creating a low-quality or unsafe actuator, for instance by targeting 400-500 hours of service life. In some cases, this is made easier through large inventories of spare parts. The UAV industry requires so many customised versions of COTS servos in small batches that servo manufacturers cannot help but re-use leftover PCBs, connectors, cases and so on in their assemblies, but which have not necessarily been designed with integration in mind. Serving such end-users can also be achieved by sacrificing a small amount of subsystem quality to save on assembly costs. For instance, the hardened steel geartrains typical of high-end servos could be manufactured and passed through quality control with wider tolerances on the cut of the gear teeth. Similarly, housings can be manufactured with simpler designs that lack features such as cooling fins or internal mounting frames. As another example, new entrants to the professional UAV space do not typically look for CAN bus or RS-485 in their servos. Not only is tracking health and performance-related diagnostic feedback for intelligent maintenance analytics outside their usual or immediate concerns, but relying on PWM can in fact be useful during early prototyping and optimisation of a UAV’s control architecture thanks to its simplicity of use. Some cost savings can therefore be made by omitting more advanced August/September 2023 | Uncrewed Systems Technology Duplex actuators (such as those shown in the X-ray above) are popular among OEMs of large aircraft, although ‘simplex’ designs are increasingly popular and sufficient for many regulators (Courtesy of Volz) Small servos with high-end components such as hardened steel geartrains are in strong demand by manufacturers and operators looking to reduce their maintenance overheads (Courtesy of Hitec)
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