Unmanned Systems Technology 026 I Tecdron TC800-FF I Propellers I USVs I AUVSI 2019 part 1 I Robby Moto UAVE I Singular Aircraft FlyOx I Teledyne SeaRaptor I Simulation & Testing I Ocean Business 2019 report

The result of these constraints are what give the UAVE its 23 kg weight, compared with the 36 kg of the RES with its electric generator integrated. It measures 530 x 320 x 290 mm (or 560 mm long, rather than 320 mm, if the electrical generator is present). The engine block is made in two halves from die-cast AlSi7 aluminium, and serves as a monobloc for the cylinders and crankcase. Each of the two cylinder heads is also made from die-cast AlSi7, and these sit atop the horizontally opposed linerless cylinders, which have a Nikasil coating. These materials were selected to save on weight and manufacturing costs. While four-stroke engines might typically use a monolithic crankshaft, Robby Moto opted for a three-part version after determining that this would reduce manufacturing and assembly costs. The engine’s operating power and torque were also deemed low enough – 25 kW and 47 Nm at 5000 rpm respectively – to make the ‘composite’ crankshaft design approach possible. The three parts are the rear crank, front crank and central section. All three have been machined from blocks of 18NiCrMo5 steel to optimise for material weight, cost and recyclability, and are subsequently carburised to reduce wear over time. Both the rear and front crank sections incorporate a crank journal about 60 mm long and 30 mm in diameter, as well as a counterweight and bearing journal. In order of contact with or proximity to the counterweight, the rear crank holds a phonic wheel for speed measurement and a distribution gear to drive the timing of the two camshafts. The central part provides a coupling for each crank pin, and has been designed to keep the rear and front cranks constrained against the torsion and bending loads created during operation. The UAVE also has two plain bearings on the propeller-side crank, as well as a single plain bearing on the rear crank close to the starter/generator. In the RES configuration, there are two plain bearings on the rear crank, close to the generator, and one on the front crank. To ensure proper lubrication of the bearings and the crank journals, a network of ducts for oil flow is drilled through the crankcase and the rear and front cranks. The main oil input points are located at the two main bearings (the ones found on each shaft section closest to the journals), and the centrifugal force of the shaft’s movement delivers the oil to the con rod big ends via the inside of the crankshaft. To do that, the oil exits from the crankshaft interior through ducts on either side of each crank pin’s circumference. The oil then lubricates the plain bearings between the crank pins and con rod big ends, as well as between the crank journals and the holes in the central part.