Unmanned Systems Technology 004 | Delair-Tech DT18 | Autopilots | Rotron RT600 | Unmanned surface vehicles | AMRC | Motion control | Batteries

70 indicates the direction of rotation. Needing no optics or internal electronics, resolvers are happy in contaminated environments and high temperatures. Differential transformers Angular position can also be measured using a cousin of the resolver known as a rotary variable differential transformer (RVDT), which produces a voltage in direct, linear proportion to the angular displacement of an input shaft. In a basic RVDT, an iron core rotates in a stator that holds a primary excitation winding and a pair of secondary output windings, the whole being contained in a stainless steel housing. The excitation winding is energised by a fixed alternating current and is electromagnetically coupled to the secondary windings, the coupling being proportional to the input shaft angle. One of the output windings is in phase with the input winding, while the other is 180° out of phase. When the rotor position directs the flux equally to both output windings, the phase difference between them cancels out their output voltages, defining the electrical zero (EZ) position. When the rotor shaft turns away from EZ, the signals from the output windings have a magnitude and phase relationship that the control electronics use to determine Autumn 2015 | Unmanned Systems Technology The ERSA-0311 is a light, high-torque redundant electro-mechanical servo actuator optimised for UAV applications (Courtesy of MTC Industries) The guts of a modern UAV servo-actuator showing the permanent-magnet brushless motor, control electronics, connector, grease-lubricated gearbox and output shaft (Courtesy of Pegasus Actuators) the direction of rotation and the angular displacement. Excitation frequency should be controlled within ± 1% to preserve accuracy, and typical measurement ranges are ± 40° and ± 80°. The RVDT has a close cousin in the form of the linear variable differential transformer. In a typical LVDT, a ferromagnetic core slides within a glass tube, around which the central excitation coil and twin output coils are wound. Connection to the mechanism whose position is being measured is via a non- magnetic pushrod. Printed transducers While they are accurate, robust and reliable, these conventional inductive position sensors are limited by their metal windings. To measure position accurately they must be wound accurately, and to provide strong signals they need a lot of wire, contributing to bulk, weight and cost. A novel alternative embodies the same inductive principles but with the conductor etched or printed onto a laminated substrate such as polyester film, paper, epoxy and ceramics. Printed construction, it is claimed, allows the sensors to be made more accurately than windings, leading to greater measurement performance from cheaper, lighter and more compact sensors while retaining the inherent stability and robustness of inductive techniques. Stable reference A stable reference with respect to gravity and the ability to sense movement about multiple axes for feedback to the control and navigation systems is often critical for many vehicles, particularly in the air and under water for attitude and position sensing. Here, fibre-optic gyro (FOG) and micro-electro-mechanical systems (MEMS) inertial sensors define the high