Sparrow / NmG
Sparrow >> Service >> Electrical >> Motor
The motor in a Sparrow is an Advanced DC 8-inch diameter motor, part #203-06-4004. It's a series-wound motor, which means that all of the current that runs through it passes through both the field coils and the rotor. Series wound motors are difficult to use as generators, so the Sparrow does not include regenerative braking. The motor is electrically reversed by a set of contactors (big, high-power relays) that can reverse polarity on one set of coils. A belt is attached to the output shaft which directly drives the rear wheel.
Corbin Motors shipped the Sparrow motor with no timing advancement, which means that the brushes are centered with respect to the fields that they interact with. This means that it will work equally well running forward or backward. Unfortunately, it also means that the motor is prone to arcing when large voltages are applied to it at high speed. Many Sparrow motors have failed due to the heat generated by arcing or even fireballing, where a set of arcs reach all the way around the commutator. This has also caused many Sparrow motor controllers to fail, as arcing causes huge sudden current draws.
By advancing the motor 7 to 10 degrees forward, you can increase the efficiency of the motor slightly while running fast. This also eliminates the arcing. The only "downside" is that the motor will run a little less efficiently in reverse. It could even arc in reverse if you were traveling at full speed and full voltage backwards.
Some ADC motors shipped with holes that allow you to advance them simply by rotating the brush rigging. Others shipped without the holes. To advance these motors, you must drill the holes yourself. Take it to a motor shop if this doesn't seem easy to you.
Myers Motors is shipping their current car, the NmG, which is based on the Sparrow, with the motors advanced.