Defiant EV3© Roadster Design Philosophy
"It's not about the cars, they're only things.
The idea, that's the only thing that really counts."
From the movie Tucker: The Man and His Dream
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In the past, I simply converted existing cars to electric power and tested the results using various motor types and battery combinations. Now, with the help of a team of experts, we are developing a "purpose built" electric car. This vehicle is designed from the ground up to capitalize on the efficiencies of an electric car; with an eye on a sporty design, that is simple to build, and able to be customize to fit an individual's unique nature.
I firmly believe that wherever possible, simple designs are the best. I think it should be a crime for "Detroit" to sell a car that you have to remove a tire in order to change the battery, or remove an engine mount and shift the engine to change a spark plug. I recognize that many people like highly engineered cars that can do everything, including make a pot of coffee for them. In fact, I heard on the radio (June 2004) that a company did a survey and discovered that the number one option that people would like to see in their car was a microwave oven! That's fine for them; however, this project is for a smaller group of people, those who like to do things for themselves. They believe that a phone is for communication (not playing games) and that a car is for transportation (not necessarily a mobile communication command post complete with TV and DVD).
No one said electric cars have to be slow. My friend, Patrick Rummerfield, held the national speed record for an all-electric car at over 239.5 miles per hour, set at the Bonneville Salt Flats in August 1999 behind the wheel of the rocket-shaped White Lightning. (He is also the world's first fully-functional spinal cord injury quadriplegic.) The current speed record for electric cars is held by
Ohio State University's Buckeye Bullet at 314.958 MPH. For a history of high speed electric cars, please visit World Electric Land Speed Records. And lets not forget Roderick Wilde, electric street rod builder, dragstrip record holder, and president of the National Electric Drag Racing Association.
With this philosophy mind, here are some of the key design considerations:
Custom Chassis - Ground-up design, with three wheels - not four! The goal is to create a highly efficient EV able to carry two passengers at highway speeds, with a range of approximately 100 miles per charge. The passengers will sit in tandem, not side-by-side. The use of three wheels reduces rolling resistance at slow speed and the aerodynamic design reduces drag at higher speeds. The low center of gravity will produce a stable ride with no more possibility of a roll-over than you would find in a conventional car. The weight distribution goal is 40/60 percent front/rear.
Drive Motor - A direct current, high voltage, 8 to 10 horsepower, series wound motor. I've tested other motors, such as shunt and compound wound, and found they did not deliver the efficiency of a good series wound motor over a variety of driving conditions. These motors are efficient, durable, and affordable! The goal is to keep the design simple. While an argument can be made that high voltage, alternating current systems are more efficient and provide better overall performance, I don't believe the improvements in performance are worth the trade-offs of higher costs and increased complexity. So, for this project, a direct current control system, similar to the one used in the Fiat 850 project will be employed. Also, I don't believe the benefits of regeneration are worth the added cost and complexity. I've seen reports that suggest that regeneration will add from 8% to 10% to the range of an electric car. However, traditional studies have shown that fuel efficiency in conventional cars can be increased by at least 10% if drivers will simply improve their personal driving habits!
Battery - High voltage, means high performance. I would not consider using anything less than 72 volts, and in fact, this project will be designed around a 120 volt system. Weight is always an issue with electric cars; therefore, readily available 12 volt, deep cycle batteries will be used for the battery pack. Battery weight, while at a minimum, is still expected to be up to 50% of the total vehicle weight, depending on configuration. (If we use one battery string, the weight will be about 25%, two battery strings will be about 50%, and the corresponding range should be between 50 and 100 miles per charge.)
Vehicle Weight - The finished vehicle is projected to have a gross vehicle weight (GVW) of up to 1500 pounds. This will include up to 900 pounds of battery weight. The basic chassis will be of tubular steel construction (frame is 13 gauge, 1 & 1/2" mild steel tubing) and the body is made of fiberglass.
Auxiliary Power Trailer (APT) - The final stage of development will include the creation of a mobile generator trailer to be attached, as required, to boost the range of the car for extended trips. The single wheel trailer will attach at two points on the vehicle's rear bumper (using two hitches instead of the traditional single hitch configuration). This approach is called "series hybrid" and relies on the internal combustion engine strictly as a power source for an electric generator. In a "parallel hybrid" system, the engine also provides some of the motive power, as well as electricity generation.
Build Notes
Initially, the project will be documented in a "How To" manual as an electric car that hobbyists can build. We have plans in place to begin custom fabrication of the vehicle. As we build the prototype over the next few months, we will post notes and selected video of the build. The "How To" manual includes a DVD that contains complete video of the build.
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