1. Intro

A motor controller is a fancy electronic gadget that modulates the amount of energy flowing through the motor and consequently the amount of torque the rear wheel produces. Since the motor in a Sparrow is a DC series-wound motor, it can be controlled quite easily by regulating the voltage applied to it. More voltage equals more current and thus more torque. At least that's the simple way of thinking about it.

A more accurate description would be that a series-wound motor has, at any RPM, a native "back EMF" which amounts to the voltage that must be applied to keep it spinning at that speed. If you apply more voltage than the back EMF, then you get current and torque. Applying a lot more voltage results in a lot more current and torque. Since back EMF is linearly related to motor speed, "flooring" the accelerator gets you more torque when the motor is spinning slowly than it does when the motor is spinning quickly. This is why a Sparrow has lots and lots of pick-up between 25mph and 50mph, but less above 50mph and little above 70mph. Below 25mph, the current required to move a Sparrow quickly is very large and most motor controllers end up in "current limit" where they can't produce any more. This is why a Sparrow seems to start moving slowly, gradually accelerating to 5 or 10mph and then seems to suddenly have more power. Note that these current limits tend to apply first to the "motor loop" as the battery loop is running at full voltage and thus needs fewer amps to supply the same watts.

These motor controllers all work by a technique called "pulse width modulation" where the current is turned on and off at some fixed frequency, usually around 15KHz, since that's mostly out of human hearing. When you apply little pressure to the accelerator, the pulses last a very short part of the 15KHz period. When you apply a lot of pressure, the pulses are "wider" and they last a longer part of the period.

Most of these motor controllers (and all of them used by Corbin) were air-cooled.

2. Motor Controllers used in the Sparrow and NmG

There were three motor controllers used during the Sparrow production run and two used in NmGs (to my knowledge.) Your vehicle could have any one of them or something else yet, particularly if yours has been heavily modified, as so many of them have. They are:

Curtis 1231 Prototype - used in early Sparrows
DCP Raptor 600 - used in mid-run Sparrows and at least one NmG
Kilovac Prototype - used in later-run Sparrows
Cafe Electric Zilla Low-Voltage 1000A model - used in NmGs

2.1 Curtis 1231

The Curtis is the most widely available motor controller on the market, though pretty much everybody seems to hate it. It's a scaled-up version of a golf cart motor controller and it barely produces enough power to keep most vehicles moving. It's notable for having no built-in safety features, meaning that everything has to provided externally. It's also notable for having a relatively low current limit. It can sustain 500A for a few seconds before it goes into thermal limit, at which point it could only sustain 150-200A. At low motor speeds, this is very little.

The version installed in the Sparrow was a prototype 156V version of their 144V design. It tended to fail quickly, particularly on vehicles where the motor hadn't been advanced. Many of the Sparrows that were fitted with this controller were refitted by Corbin or others with other controllers. There is at least one company successfully rebuilding these, so if you have a Sparrow with a failed Curtis, you should consider that route.

2.2 DCP Raptor 600 amp

This motor controller was built by the company that eventually became Alltrax [http://www.alltraxinc.com], which currently deals only in low-voltage controllers. They are rare at this point, as most of them failed in motor fireballs. Again, see the section on motor advancement for fixing issue. You can get a new Raptor 1200 built for you these days by Peter Senkowsky. When these work, they work well. The 600A current limit was better than the 500 from the Curtis and thermal issues weren't as bad, so they could actually produce that 600A. If you have a 1200A version, you have very quick car indeed.

2.3 Kilovac Prototype

Kilovac is still in business, though they aren't currently building traction motor controllers. These controllers were used in most of the hatchback ("pizza-butt") Sparrows. They had a better reliability record than the others, but they still failed pretty frequently, usually due to heat and lack of motor advancement. Ron Anderson now rebuilds these. See www.black-sheep.us . I don't know what the current limit was, but performance is acceptable. Pictures of one of Ron's rebuilds are here Kilovac Rebuild.

2.4 Cafe Electric Zilla Z1K-LV

This is the gold standard of DC traction motor controllers. They can be purchased today from http://www.cafeelectric.com/. The version of the Zilla in an NmG is the 1000A 156V (Z1K-LV) model. There has only ever been one failure of a Zilla in the field and it was in a dragster pulling 2000A at 360V. (See http://www.plasmaboyracing.com/whitezombie.php.) If you have one of these, you have a lot of power and tremendous features and reliability. One of the notable reasons for its reliability is that it is water cooled, so any installation in a Sparrow must involve a water tank, small radiator, a pump and some plumbing.

Jake Oshins