Unmanned Systems Technology 015 | Martin UAV V-Bat | William Sachiti | Sonar Systems | USVs | Desert Aircraft DA150 EFI | SeaCat AUV/ROV | Gimbals

70 Focus | Gimbals weight limits set by military and civilian customer requirements and expectations. That drives the use of advanced engineering materials such as fibre- reinforced plastics and lightweight, high- strength metal alloys. A question of stability One of the most demanding engineering aspects of stabilised electro-optical (EO) payloads is to achieve a stabilisation level that first keeps the sensor on the target throughout the system’s entire field of regard, then is appropriate to the field of view of the optics. (The field of regard is the total angular view that the system can capture, and includes the sensor’s field of view and the turret’s range of movement.) Irrespective of turbulence from the air or vibration from the platform’s motor or propeller and any unwanted resonant frequencies, the system needs to close the control loops tightly, all within demanding Size, Weight and Power (SWaP) budgets. There is no magic bullet for this; it is a matter of attention to detail and sound systems engineering. However, picking the right servo motors and designing digital and analogue control loops are critical elements of the electromechanical solution that will achieve the required level of stabilisation. Improvements in overall stabilisation rely on incremental improvements in many component technologies, including software that tightens digital control loops, electronics hardware, servo motors and the related encoders. Suppliers are improving and miniaturising all of these on a yearly basis. The number of stabilised axes is often used as a shorthand description of a gimballed payload to indicate the level of stabilisation and, by implication, its cost. While useful though, it does not really illuminate the process that systems engineers go through when specifying a solution to a requirement. If the system needs to stabilise a sensor with an instantaneous field of view (IFoV) of, say, 50 microradians (about 0.003 º ), the system must hold the line of sight within a much smaller range of angular movement from the point of aim – ideally half that or less. The IFoV itself is defined as the angle subtended by a single detector element on the axis of the optical system, and is a calculated number that takes into account the focal length of the lens and the pitch of the focal plane array August/September 2017 | Unmanned Systems Technology A three-gimbal tilt/roll/pan system with the camera platform directly supported by the tilt gimbal (Courtesy of DJI) Some of the stabilised axes revealed with the covers removed from HoodTech Vision’s Alticam 05-EO5 system (Courtesy of HoodTech Vision)