THE SPARROW STORY
Drivetrain Update: Aluminum Swingarm and AC Motor
This archived update summarized the drive package fitted to the redesigned Sparrow. It paired Corbin's patented single-sided swingarm, now made in aluminum, with a three-phase AC motor from HPEV rated at 30 hp, regenerative braking, and a Gates belt drive to the rear wheel.
From the Sparrow archive. Product plans, events and availability described here belong to the original historical period.
From DC to a three-phase AC motor
The roughly 300 original Sparrows built from 1998 to 2003 used DC motors, which Corbin described as reliable and long-lived. For the revival, the team chose a three-phase AC motor. In general, AC drives of this type offer high efficiency, allow the motor to act as a generator during braking, and let top speed be set in software. Corbin's related pages described the HPEV unit as producing 30 hp, with peak and continuous ratings quoted elsewhere as 35 and 10 hp.
The system was proven first on Mike Corbin's own car, original production Sparrow number 100, which was retrofitted with the AC drive and used for extended driving. That test mule later climbed Mount Washington in New Hampshire during a revived Electric Vehicle Regatta, reaching the summit without drama and recovering some charge on the descent through regenerative braking.
Swingarm, belt and brakes
Corbin traced the single-sided electric drive swingarm to 1995. Mounting the motor as a structural member of the arm places its weight favorably and lets all three wheels share a common fitment. Corbin's Vince Zavala designed the new billet motor mount and swingarm in the company's revamped machine shop, with the aluminum construction intended to trim gross vehicle weight. The update cited United States Patents 6,464,030, 6,883,629 and 5,960,901.
Power reaches the rear wheel through a Gates belt with an integrated tensioner. Belt drives run quietly and need no lubrication, which suits an electric vehicle. Stopping at the rear combines a hydraulic disc brake with a mechanical brake, in addition to the regenerative braking that feeds energy back into the pack.