Issue 37 Unmanned Systems Technology April/May 2021 Einride next-gen Pod l Battery technology l Dive Technologies AUV-Kit l UGVs insight l Vanguard EFI/ETC vee twins l Icarus Swarms l Transponders l Sonobot 5 l IDEX 2021 report

64 A 24-1 tooth gear around the Big Block’s flywheel is used for sensing crank speed and position, with a speed sensor installed next to the flywheel. Power for both engines’ control systems comes from a stator installed at the flywheel. Some of its coils power a voltage regulator at the ECU (for stable power distribution to the sensors and throttle control) while others connect to a separate onboard vehicle battery. Bruener adds that this arrangement isolates the EFI from electrical spikes. Thermal management of the engines is handled by air-cooling, with fins distributed around the cylinders and cylinder heads. Unlike the smaller engine though, the Big Block integrates an O 2 sensor and cylinder head temperature sensor as standard, enabling a broader range of data analytics, thermal or otherwise. “In its early days, both air-cooled and liquid-cooled versions of the Big Block were available, but over time the liquid-cooled one was discontinued because customers preferred the lower maintenance requirements of the air- cooled version,” Pomeroy notes. Intake and valvetrain As mentioned, the smaller engine’s throttle-body injector assembly sits atop the front of the engine, from which the fuel- air charge is separated into two manifold channels for passage into the cylinders. The injector in the throttle body is supplied by Aisan. It was selected for its ability to precisely measure and finely control the accuracy with which fuel is atomised and distributed into the airflow. It sprays fuel at a 45 º angle, towards the back of where the throttle plate sits, with injection timing commands coming via the ignition coils and ECU. These are installed towards the bases of the cylinders, and come with Kokusan-Denki’s embedded algorithms to determine exactly where in the combustion cycle they are, and therefore when to fire. A cyclonic air cleaner can also be integrated atop the engine, over the manifold, to enable protection against airborne debris entering the engine, for operations in dusty or grassy places. “Of course, many UAV applications might forgo that, to reduce weight further,” Ihrig adds. With TMAP and speed data controlling fuel-air ratios and timing, the valvetrain controls entry of the charge into the cylinders and evacuation of exhaust gas. The valve arrangement consists of a fairly standard pushrod valvetrain. Each cylinder has one intake valve and one exhaust valve, and each valve’s centreline is set parallel to the cylinder bore, with the ports angled to optimise fluid flow. Valve lift and duration are governed by a camshaft, which has been cast from ductile iron for both Small and Big Block engines, and sits above the crankshaft. A drive gear on the front crank journal drives the cam, which has teeth in order to serve as the driven sprocket. The camshaft features four lobes for the four engine valves, two for the intakes and two for the exhausts (in order, going backwards from the flywheel). The cam lobes are hardened to better resist wear from friction as they push against flat tappets, which in the 23 bhp engine connect to steel pushrods for the intake valvetrains and aluminium pushrods for the exhaust. April/May 2021 | Unmanned Systems Technology The Big Block’s intake valve (left) measures 36.8 mm across, while its exhaust valve (right) is 32.5 mm wide There was a bigger jump in power output for the latest versions because the ports were angled. It’s now easier to get airflow into the chamber