Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

40 If metal AM is used to make complex sections such as monobloc parts, it could save gimbal manufacturers a lot of time and money, as well as being useful for identifying where material can be removed to save weight while maintaining balance and strength. However, further improvements in the technology are needed for it to provide comparable tolerances and consistency to CNC-machined parts, as the latter still produces more structurally sound and consistent components, and more cost- effectively too. Most high-end gimbals are made from CNC-machined aluminium alloys, to provide a high strength-to-weight ratio and a low thermal expansion coefficient. Also, they do not degrade over time from UV radiation, vibration or any of the other problems that adversely affect plastics. Their thermal conductivity helps draw heat from embedded processors too, conducting it to the outer hull to be dissipated by the surrounding airflow during flight. Composite materials are also used for some structural parts in gimbals: fibre glass and carbon composite provide higher strength-to-weight ratios than aluminium. However, there are limitations to their usability in gimbals. Producing composite material parts relies on using complex moulds and techniques, which are unsuited to the iterative processes typical of gimbal development and to the redesigns needed for accommodating new detectors, processors and other technologies. Also, gyro-stabilised gimbals can require hundreds of holes and threads: drilling those holes into composite parts breaks their fibres and encourages delamination. Balancing Advances in CAD software and the computer processors for handling them also help greatly in simulating the CoG and weight distribution across payload housings, which contributes to how well- balanced each sensor will be on its gimbal. The more accurately the balance can be modelled, the less work will be needed later to get gimbal balance correct. It also means less current will be needed for the motors to control the pointing and movement of the cameras. That is another important factor, because the actual process of measuring and improving gimbal balance is cumbersome. While the theory behind it is simple – you merely need to measure which side of each rotating assembly is heavier – putting it into practice involves repeatedly dismantling and reassembling a system’s components, in order to measure the balance on each gimbal individually as well as how the overall system balances out when those parts are bolted together and interacting as they would during normal use. As might be expected, a lot of trial and error is involved – adding and moving counterweights, or changing the position of components such as PCBs or encoders – to try to balance the weight across the gimbal system. That often means placing each gimbal on a specialised weighing scale, with very fine bearings or needles installed to allow the scale to rotate freely. The heaviest part of the gimbal will then rotate to point downwards, so weight can be added on the opposite side. However, there can be tiny but significant variations in how weight is distributed across and throughout the gimbal with each reassembly, with parts such as wires bending slightly differently each time, so extreme precision and care is needed. Many companies have developed their own proprietary methodologies for optimising the balance. Additionally, the bearings on the gimbals and weighing scales can stick owing to the friction between them. If that happens, the balance measurements will be inaccurate, and the gimbal designer will have no real information on the improvements they have tried to make to the structure’s balance. More sophisticated, automated instruments are available for measuring the imbalance in each axis of a gimbal, but while they eliminate the need for dozens of rounds of disassembly and reassembly, they remain cost-prohibitive for gimbal manufacturers to acquire. Geo-pointing and tracking IMUs are critical not only for gyro stabilisation, but also to provide precise geo-pointing and tracking. Intelligent, August/September 2019 | Unmanned Systems Technology Inertial data from a UAV’s navigation system can be used to augment the stabilisation, geo- referencing and object tracking capabilities of a sensor gimbal (Courtesy of UAV Navigation)