![[Figure 1.1]](figure_1_1.gif)
For thousands of years, humans have devised various methods of transportation. Whether they were horseback riding or relaxing inside a limousine, people have wanted personal, long- distance mobility. Today's automobiles go much faster and further than the carts of ancient times, but they can also leave behind a terrible trail of environmental damage. Unlike human-powered vehicles, the typical automobile uses "readily" available fossil fuel, which reduces the need for efficiency. In this thesis, a self-propelled, environmentally sound, socially acceptable, and affordable vehicle is described that combines efficient machine design with modern technology.
TRANSPORTATION METHODS
There are a wide assortment of transportation methods, ranging from cross-country skis to supersonic airplanes, now available. However, practical concerns such as cost and convenience quickly reduce the options and people typically choose the automobile for personal trips. There are also many mass-transit options, such as buses and subways, but these do not provide the door-to-door service that many people desire. Although not as well accepted, human powered options, such as walking, bicycling, and even roller blading also provide excellent individualized, local transportation.
Today, there are roughly half a
billion cars on the streets worldwide.
Of these, approximately one third are
in America, where each car is driven
an average of 10,000 miles per year
[Renner, 1988]. However, as can be
seen in Figure 1.1, over 75 percent of
all automobile trips are less than ten
miles long. This makes human-powered options much more viable
than people are
conditioned to think.
It therefore comes as no surprise that in many less industrialized nations, the bicycle (or its local variant such as the rickshaw) is the primary source of transportation. There are now nearly one billion bicycles in the world, with 100 million being produced every year. In 1988, there was one bicycle per four people in China, but only one car per 1000 people. The same year in the United States, there was one auto for every two people and, surprisingly, an equal ratio for bicycles. However, of the over 100 million bicycles in America, data shows that only one in 40 is used for commuting. The rest are used for recreation or simply collecting dust. Additionally, it is estimated that two out of three bicycle users in this country are children [Lowe, 1989 and Braddock, 1990].
The bicycle has been described as "the most important technical invention of the nineteenth century. With the possible exception of the wheel itself, no other invention has ever led to a more extensive range of research, experiment, inventiveness, development, and social change . . . " [Van der Plas, 1983, p. 152]. As a "humane and efficient machine, [the bicycle] played a central role in the evolution of the ball bearing, the pneumatic tire, tubular construction, and the automobile and airplane" [Wilson, 1973, p. 81]. Ironically, it is these modern machines that are now often blamed for a variety of problems.
ENVIRONMENTAL CONSIDERATIONS
Since the advent of the internal combustion engine, automobiles have been the predominant form of personal transportation in the United States. Unfortunately, the production and use of the needed fossil fuel has resulted in extensive pollution problems. With energy use increasing several times faster than the population is increasing [Kraushaur and Ristinen, 1993], it is obvious that people must change their consumption habits. As one bicycle-lover summarized, "it is a very simple situation: motor vehicles are filling the air with deadly fumes and noise, recklessly wasting a dwindling supply of natural resources, and killing and injuring people" [Ballantine, 1987, p. 349].
Considerable research has been undertaken regarding alternative energy sources, such as solar, wind, hydro, and geothermal power. Unlike fossil fuels, these forms are impossible to transport. Therefore it becomes necessary to store the power as a different form of energy. As a possible solution, fuel cells are now being developed, but such technology is thought to be many years away. However, most any source can be used to generate electricity which, in turn, can charge batteries. Although physically heavy for the amount of power stored, batteries can be transported as needed.
In addition to having storage limitations, alternative power is relatively expensive to produce. Therefore, when designing products that rely on such sources, high efficiency is extremely important. Figure 1.2 shows that among the various types of transportation, the bicycle is the most efficient, while the common automobile is by far the least efficient. This inefficiency of automobiles is heightened since internal combustion engines only achieve optimum performance when fully warmed-up. Combining figure 1.3 with the earlier statistic that most car trips are less than ten miles long, we see that cars rarely operate at peak efficiency, particularly as the outside temperature drops.
SOCIOLOGICAL FACTORS
Lowe observes that "today many people who choose to drive rather than walk or cycle a short distance do so not merely for convenience, but also to insulate themselves from the harshness of a street ruled by the motor vehicle" [1989, p. 14]. This is part of a vicious cycle that results from industrialized society. As more people use cars, the associated air and noise pollution increases. In turn, people move further away from the city, but more cars are then used to go longer distances. As a result, the city is enlarged, but so is the area of congestion and pollution. This leaves the basic problems unsolved, so the cycle continues.
This modern mindset is both highlighted and ridiculed in the story of Hymie Dunderhead by Ballantine [1987, p. 349]: "Hymie has worked hard to get his idiot crate. From day one he's listened to his parents, to the boob tube, to his school masters - Hymie has cooperated with his society, however insane, and now he wants his reward, some kind of evidence of his cooperation as a sop to a malformed ego - and that just happens to be a 140 mph Turbo-Dynamic Special..." Ballantine also states that "ego, status, and territory are all closely intertwined with motor vehicles . . .". One needs only to view a television commercial to confirm this attitude.
At the same time that American society equates cars with excitement, bicycles have the opposite reputation. "It may well be very healthy, but it is a deadly bore and is totally impractical . . . nobody in the USA . . . seems to believe that a bicycle could actually be used to get somewhere" [Van der Plas, 1983, p. 167]. Bicyclists must not only forego luxuries such as stereo radios and cellular phones, but must also physically exert themselves and be exposed to the elements.
DEVELOPMENT SPECIFICATIONS
There is a definitive need for a new method of individualized transportation, which is environmentally sound yet socially acceptable. In this thesis, a potential solution is developed, based on the common bicycle. Having evolved for the limited power resources of the human body, bicycles are extremely efficient machines. With millions currently in use, and the underlying physics well-understood, the challenge is to select a suitable form of mechanized propulsion. Unfortunately, the small frame and lack of body provide no protection from rain and snow and dictate relatively low speed operation. However, this small size does allow the rider to continue through stopped traffic, making up for lost time. Also, with power available, some automobile features, such as a radio, could be provided.
In order to be truly environmentally sound, the source of power must be carefully chosen. Since alternative energy sources are not generally transportable, energy stored in batteries is the only practical solution. To make a self-sustaining system, the batteries could be recharged with power from a "green" source, such as small-scale hydro, solar, or wind. With batteries as the power source, it is only logical to use an electric motor to propel the bicycle. This system provides the additional benefit of being easily adapted to recapture energy normally lost as heat during braking.
With the exception of an adequate low-voltage, high-current motor controller, all other parts needed to make an electrified bicycle are readily available. However, high- power semiconductor technology has advanced rapidly in recent years. Therefore, this thesis focuses on the design and implementation of a semiconductor controller for an electrically powered bicycle.
To meet the goals presented in this chapter, the electric bike will:
Furthermore, to be legal as a "motorized bicycle" or "moped" on all streets (other than "interstate" highways) in the state of Massachusetts, it must:
Also, to meet the requirements of the American Tour De Sol, an annual competition and display of electric vehicles, the bike needs to:
Above all, the electric bicycle must meet the general requirements of:
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Design of an Efficient and Economical Electric Bicycle / jcoate@tufts.edu