THE SPARROW STORY
The Corbin Single-Sided Swingarm Drive Train Explained
The rear of the Sparrow is built around a single-sided swingarm with the electric motor integrated into it as a structural member. Corbin developed this arrangement in 1995 for the original Sparrow and holds United States Patents 6,883,629, 6,464,030 and 5,960,901 covering it.
From the Sparrow archive. Product plans, events and availability described here belong to the original historical period.
Layout and motor
A single-sided swingarm supports the rear wheel from one side only, the way many motorcycles do. On the Sparrow this places the motor's mass low and close to the pivot, which the team considered favorable for weight distribution. It also leaves the wheel exposed on the other side, so all three wheels can be removed and swapped easily.
The modern prototype uses an HPEV three-phase AC synchronous motor rated at 30 kilowatts. In the configuration the team described, the drive produces about 30 horsepower, enough to take the Sparrow from a standstill to 60 miles per hour in around nine seconds. Top speed is set in software and was programmed to 80 miles per hour at the time. The swingarm and motor mount for the prototype were designed in aluminum by Vince Zavala in the Corbin machine shop.
Transmission, regeneration and braking
Power reaches the rear wheel through a Gates belt drive with an integrated tensioner. Belt drives run quietly, need no lubrication and tolerate small alignment changes as the swingarm moves through its travel, which suits a motorcycle-style rear end.
The controller provides regenerative braking, letting the motor act as a generator under deceleration and return energy to the pack. Friction braking at the rear is by a disc with both hydraulic and mechanical actuation, the latter serving the parking brake function.
