Unmanned Systems Technology 020 | Alpha 800 I Additive Manufacturing focus I USVs insight I Pegasus GE70 I GuardBot I AUVSI Xponential 2018 show report I Solar Power focus I CUAV Expo Europe 2018 show report

28 electronic unit to control the engine and the payloads because nothing on the market offered the flexibility it needed for the different configurations customers wanted. Escarpenter explains, “This is the power and communications module [PCM], which handles all power distribution in the UAV for payloads and servos, and provides a redundant power source for the autopilot. It has a multiple input, multiple output [MIMO] radio link integrated into it and also contains the ECU.” In addition to its engine control duties, the ECU also monitors the fuel level, and voltage and current consumption, enabling Alpha to program in actions such as switching off the payload if it detects an under-voltage to save battery power for essential systems. Belt and pulley transmission The engine drives the main and tail rotors via a centrifugal clutch and a system of toothed pulleys and GRP belts. The main transmission and tail rotor drive belts are 14 and 10 mm wide respectively. The main drive belt runs under the fuselage from a pulley on the end of the vertically orientated crankshaft to a larger one, providing the first stage of speed reduction between engine and rotor. That drives a vertical shaft, on the upper end of which is the pinion gear that drives the transmission’s main ring gear, providing the second reduction stage. Fixed to this vertical shaft, between the first-stage pulley and the ring gear, are two more pulleys driving toothed belts. A short one runs forward to the alternator while a second, much longer one, runs back down the tail boom to drive the tail rotor, going through a 90° twist to turn the horizontal tail rotor shaft as it does so. “This has proven to be the simplest and most reliable configuration,” Escarpenter says. “For example, using a torque tube for the tail rotor drive has always been more problematic. “However, the belt can generate static electricity, which if not handled correctly can create interference with systems including the magnetometer and some sensitive analogue sensors.” The main rotor has a one-way bearing that in case of an engine failure would uncouple the tail rotor from the main rotor. That would save all the main rotor’s kinetic energy for the glide but lose tail control during auto-rotation, albeit retaining directional control by means of pitch and roll. Electrical supplies The main source of electrical power is a modified motor from T-Motor, repurposed as a brushless alternator to provide up to 200 W at 24-28 V. Alpha added a third bearing to increase support of the alternator shaft. The alternator is rated for up to 400 W of continuous power. Alpha limits the consumption of the electrical loads to 200 W, however, in line with the safety margin that the company applies to the June/July 2018 | Unmanned Systems Technology Dossier | Alpha Unmanned Systems Alpha 800 The tail rotor is driven by a rubber belt and alloy pulley. The belt itself is driven by a shaft off the main transmission (Author’s image) The alternator, in green, is a repurposed motor. The shaft that drives it also powers the tail rotor (Courtesy of Alpha)