Unmanned Systems Technology 025 | iXblue DriX I Maintenance I UGVs I IDEX 2019 I Planck Aero Shearwater I Sky Power hybrid system I Delph Dynamics RH4 I GCSs I StreetDrone Twizy I Oceanology Americas 2019

36 Focus | Maintenance Technicians might also take note of the torque on the fasteners, according to the tolerances of the areas where they are placed. If they’re too loose, vibration during flight could cause them to spring off, and the torque and vibration generated by BLDC motors can even unscrew the fasteners on their enclosures if they are not tight enough. If they’re too tight though, propeller hubs and circuit boards can crack, especially during hard landings or shipping. The use of a small torque wrench (much smaller than an automotive one) can therefore be ideal for correctly gauging the tightness of fasteners in commercial UAS airframes. For most of the airframe, visual and manual inspections are often enough to identify where maintenance is needed. Problem areas will include chipped props, damaged connectors and motors clogged with saltwater residue. Outright replacement of inexpensive parts such as propellers or landing struts is common. For more costly parts such as camera payloads, however, a gimbal adjustment (such as swapping out a bent pin) or a camera recalibration (including ‘baking’ the camera in an oven-like chamber) can be performed before considering replacement. That can vary though depending on whether the camera was supplied with the UAV or was acquired separately. In the latter case, it is rarer for UAV maintenance depots to have the hardware and software necessary to perform recalibrations. Following this, plugging the UAV into a laptop and checking that its onboard systems have all the latest firmware and driver updates would be key. Dismantling enclosed systems such as GNSS-IMUs, autopilots or comms receivers is rare, as it can void the warranty on such systems. For severe malfunctions, most maintenance companies keep close ties with component manufacturers in order to rapidly acquire replacement subsystems, sending damaged avionics back to the supplier for repairs or disposal in the meantime. A maintenance technician will often encounter signs of any attempted self- repairs, such as when a UAS operator has soldered a wire themselves. While that might appear to work temporarily, and a UAV can fly again afterwards, it often reduces the craft’s lifespan and must still be reported by maintenance companies to the appropriate manufacturer, who might then refuse to replace the part. For accurately gauging the causes of (and therefore solutions to) issues with UAVs, some maintenance teams have performed several hours of forensic operations aimed at recreating the circumstances that led to some particular damage. This can range from simply checking telemetry logs prior to a crash to recreating the crash with a similar UAS model. Such demonstrations have found, for example, that where a UAV fell from the sky because a fastener on a propeller came loose, this was then exacerbated by the pilot increasing the throttle to try to get the craft to pull out of the dive, which led to severe vibration that pulled the airframe apart. Tests like that can be critical for establishing the kind of third-party maintenance documentation that aviation authorities and UAV insurance providers require for tracking the health of an aircraft, across a well-documented paper trail for maintenance and liability purposes. Field maintenance Larger UASs operating from airfields and other operational sites undergo a lot of maintenance before each launch. For avionics, these comprise many self-checks. The autopilot for instance runs health checks on each flight sensor and control surface, and the operator tracks these to ascertain that sensor read-outs agree – for example to ensure that all three IMUs in a triple-redundant autopilot are producing the same outputs for a given input. Much of this process is now automated. If for example a temperature reading within the autopilot is outside operating parameters, or a voltage is too low, that will automatically be displayed as an alert, and the autopilot will not pass that pre-flight check. Basic troubleshooting can then be performed. For example, if there is an erroneous input voltage to one of the sensors or computers, a technician might examine the power supply to see if that is causing the issue. A damaged servo can also trigger an alert of non-responsiveness, poor April/May 2019 | Unmanned Systems Technology As well as performing automated self-checks, onboard systems should be examined for problems such as loose wiring harnesses and damaged connectors (Photo: Christian Clausen, courtesy of US Air Force)