Overview
A foldable electric motorbike I worked on, focused on the battery pack and drivetrain. The battery is a custom 20s12p pack of P42A 21700 lithium-ion cells, delivering 74V nominal and up to 84V at full charge, with roughly 20kW peak output and 7.5kW continuous. Power runs through a Nucular P24F controller into a QS138 motor, reaching the rear wheel via a two-stage 7:1 reduction on custom 4130 chromoly sprockets — milled from quarter-inch plate — running a 520 chain.
The frame is two parallel 6061 aluminum plates joined by bent, welded 5052 sheet metal, with a five-blade chromoly steel swingarm fabricated on a custom jig. Because the bike is designed to fold, the drivetrain needed a jackshaft at the swingarm pivot just to keep chain tension constant through the folding motion — a constraint that ended up shaping the entire layout. Estimated 0–100 km/h is about 3.5 seconds, at roughly 70kg for the bike alone.