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

59 Background The history of this vee twin goes back several decades, having evolved from a four-stroke opposed twin-cylinder design produced primarily for tractor drivetrains in the late 1970s. “That was a well-balanced engine with good performance, outputting 18 bhp and with both vertical- and horizontal- shaft configurations available, but its opposed twin-cylinder configuration was quite wide,” recounts Pat Bruener, principal engineer at Briggs & Stratton. “So it didn’t package well for a lot of applications. By contrast, a vee twin packages really well for all sorts of vehicles, and it so happened that our r&d team back then was working on a vee-twin L-head engine. All the engines we made back then had L-head valve configurations, since the simplicity and compactness of that design approach also worked well for utility engines.” Around the mid-1980s, one of Briggs & Stratton’s customers in the generator sector was designing a vee-twin overhead valve engine. They approached Briggs & Stratton with a request to complete the design for them, so in 1987 the original Small Block vee twin was developed, with 30 cu in (479 cc) of displacement. Briggs & Stratton has since made iterative improvements to the engine’s design and added larger, 35 cu in and 38 cu in displacements. The biggest and most recent advance is the development of the EFI/ETC system for the engine. “The first application to use this new, CAN-based system was Rosenbauer’s RS14 portable fire/rescue generator,” Bruener says. “Rosenbauer was using the carburetted 23 bhp version to power portable generators for its lightweight and back-up rewind start capability. Replacing the carburettor with CAN-based EFI/ETC technology in 2017 enabled a new wave of remotely controlled and autonomous applications for us.” In addition to generator units for Rosenbauer and others, both versions of the engine have also been adopted in a range of off-road vehicles that need long endurance in harsh environments, including remotely operated grass and turf management vehicles – with fully or semi- autonomous UGV mowers expected Briggs & Stratton Vanguard EFI/ETC vee twins | Dossier The original engine was well-balanced but its opposed twin-cylinder configuration was quite wide, so it didn’t package well in many cases Unmanned Systems Technology | April/May 2021 Windracers’ Ultra UAV integrates two Small Block EFI engines, for carrying 100 kg of aid over 1000 km (Courtesy of Windracers)