USE Network launch I UAV Works VALAQ l Cable harnesses l USVs insight l Xponential 2020 update l MARIN AUV l Suter Industries TOA 288 l Vitirover l AI systems l Vtrus ABI

72 Electrical systems The permanent magnet starter/generator is mounted on the back end of the crankshaft, inside its own cylindrical housing chamber within the engine block but separate from the crankcase. This was done to protect the sensitive windings and magnets from corrosion and heat without relying on coatings, which Kehe’s team predicted would be more expensive than simply machine-cutting a separate space as a generator housing. The TOA 288’s standard-issue starter/ generator generates up to 1 kW of power (at 5200 rpm and above), and is designed with double windings and three independent phases for redundancy. The current produced is low enough that aluminium fins off of the back of the engine are enough to dissipate any heat the generator builds up inside its chamber. As mentioned, if users need more electrical power, an extra generator can be mounted on the forward end of the crankshaft between the engine block and the power take-off (PTO). “We can also just install a bigger generator, rather than adding one between the engine and generator,” Kehe notes. The spark plugs rely on capacitive discharge ignition, which Kehe and his team regarded as the optimal choice for minimising power and weight. He says, “If you go for a big, brick-like coil, you can transfer more energy but you don’t get a higher voltage, and all that energy storage is detrimental to your weight management. So we’re happy to use a capacitor, and the coil serves to ramp up the voltage.” Component design and machining While the prototype crankcase was originally cast, it is now machined directly from aluminium billet, for reasons of lower weight and production consistency. “I’ve seen many times how difficult it is to get cast parts through modern standards of quality control,” Kehe says. “When you X-ray cast engine sections, you get random distributions of air bubbles, variations in structural integrity and so on. It’s a real risk for anyone looking to go into high-end engineering, especially if they invest in casting moulds that can’t be changed.” Key to this has been access to Suter’s milling department, which is staffed by three engineers who are well-versed in CAD/ CAM manufacturing automation software. “We machine the crankshaft in-house June/July 2020 | Unmanned Systems Technology The engine block is machined in-house from hardened and tempered aluminium billet The engine uses custom-designed hypereutectic pistons to ensure they will last a long time against the thermal stresses from combustion The cooling fins have been geometrically optimised to conduct heat out of the cylinders and heads