Project Roark : Electric Dirtbike

Project Roark is a solo design and build of a high-performance electric dirtbike, designed from scratch with manufacturability as the core constraint. Every major component — frame, swingarm, battery pack, axle, and sprockets — was either designed and fabricated from raw stock or carefully selected and integrated. The goal was to produce a capable off-road machine that could be replicated by anyone with access to a CNC mill, a TIG welder, and a press brake. The frame is built from two parallel 6061 aluminum plates, joined by bent 5052 sheet metal and welded together. The swingarm is a five-blade chromoly steel fabrication, assembled on a custom jig. The bike is designed to fold, which required a jackshaft at the swingarm pivot to keep chain tension constant throughout the folding motion — a constraint that shaped the entire drivetrain layout. The battery is a custom 20s12p pack using P42A 21700 lithium-ion cells, delivering 74V nominal and up to 84V at full charge, with a peak output of around 20kW. Power is managed by a Nucular P24F controller, one of the more capable units available at this scale. The motor is a QS138, driving the rear wheel through a two-stage 7:1 reduction using custom 4130 chromoly sprockets milled from quarter-inch plate, running a 520 chain. Key specs: — Peak power: 20 kW — Continuous power: 7.5 kW — Voltage: 74V nominal / 84V max — Battery: 20s12p, P42A 21700 cells — Motor: QS138 — Controller: Nucular P24F — Gear ratio: 7:1 (two-stage jackshaft) — Estimated 0–100 km/h: ~3.5 s — Total weight: ~70 kg (bike only) For the full design breakdown — battery calculations, swingarm FEA, drivetrain geometry, and fabrication notes — see the design journal. Thank you to the sponsors : 1517 Medici Grant, Alex Balfanz, SendCutSend, Nucular.