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Electric Car Drag Racing
rumba writes, "The National Electric Drag Racing Association (NEDRA) exists to increase public awareness of electric vehicle (EV) performance and to encourage through competition, advances in electric vehicle technology. This organization's first big event of the year is coming up next weekend. Anybody in the Phoenix Area going to this? There's no slots on these babies. Still, I'd hate to see the utility bill."
Someone once said (I can't recall who, unfortunately) "The best way to extend the range of an Electric Vehicle is a rental car." (or something like that.)
How often do you drive from Akron to Detroit? How far do you really drive on a daily basis? One of the problems is that the general public is conditioned to thinking of refueling as a pain in the butt, hopefully done no more than once a week (Often in the rain or snow, or late at night when you'd rather be in bed, or when you're late for a meeting.)
Not so with EV's. You come home at the end of the day, pull into your nice warm garage, and plug the car in. The next morning, you've got a full charge. Around here, (San Francisco Bay Area) there are all kinds of places for an "opportunity charge." Offices have EV charging stations in the parking lot, as does BART (the local, inter-county train system,) and even Fry's Electronics. Even in Akron or Detroit, I'm told that many parking lots have public outlets for block heaters -- which work fine for most EV chargers.
For driving across country, generally speaking, EV's are not the answer. But for day-to-day commuting of, say, 50 miles or less each way, (and if you commute more than that you need to re-evaluate the value of your time!) they work great. For running errands around town, they're great.
You don't want to use your EV to drive to visit your mother-in-law, but how often do you do that? You don't want to use an EV to drive the kids to Disneyland, but that's not an enjoyable task in any vehicle -- you're better off flying anyway. You're a travelling salesman and you drive 150 miles a day? You need gas. But for the rest of us, EV's would work for most of our driving.
On a side note, I was in Yosemite a few years back (9/22/95, to be exact) to do a little backpacking and attend the unveiling of some electric busses that were to be used in the valley. There were quite a few EV luminaries in attendance with samples of their work, including one gent who had just driven his electric Honda CRX from Washington DC. (He used, of course, a high-efficiency gas generator built into a trailer to get something like 60mpg.)
If you're looking at distance per pound, yes. But that is not the only criteria. There are others such as cost per mile (EV's win), convenience of refueling (EV's win for day-to-day, Gas wins for the unusual), noise (EV's win), power (EV's win), and so on.
Stupid people will be persecuted to the fullest extent allowed by law.
Obviously a joke, or at least close, but the same argument (Electric cars are not better for the environment) has been pulled out of many hats, not just for cars but buses and trains and all sorts of things. The simple fact is that the argument doesn't hold water.
:)
1. The current state of the art in low-pollution petrol powered cars has almost nowhere to go. Further research is giving fewer and fewer returns in methods of making mobile petrol-based propulsion systems cleaner. On the other hand, factory scale plants using both petrol and other forms of raw material such as coal have been making large advances, with many by-products of the electricity production going into creating other useful products.
2. Research on electricity based transport is advancing rapidly, greater efficiencies in all areas are constantly being achieved, with new software able to micro-manage power consumption, newer battery methods and flywheel technology offering better storage per gram, and longer life for all components.
These alone are excellent reasons why electric cars, although they may _possibly_ be less environmentally friendly right now taking into account the entire supply chain, are the future.
Their primary attractiveness as far as the environment goes is the shifting of by-products to large generation plants where the benefits of scale and space can be used to filter and reuse pollutants. They are also demonstrably quieter, and in many cases can take advantage of their electrical nature to make driving as we know it today more fuel efficient (brakes tied into flywheels mean that stop-go traffic would cost far less in energy terms, and wear out your brake-pads less).
I'm looking forward to it
You can't win a fight.
Although for that matter, I'm pretty impressed with a power supply that can deliver that kind of current, too. (Quick calculation on xcalc...) Conservatively, that comes out to around 100 KW from a battery!
Quantum mechanics: the dreams that stuff is made of.
Right now, IMHO, the best candidates for near-term energy storage in EVs are ultracapictors and flywheels. Both have a clear advantage over batteries in terms of discharge rates. Ultracapicitors currently have energy density issues and flywheels have some efficiency issues. However, flywheels have the advantage of requiring a controller to convert to and from kinetic energy. It would be relatively easy for the controller to be linked to the power management computer via a digital command coax. In an accident, there would be very little risk of electrical disharge, even if the output terminals are shorted.
I eas very surprised at the ammount of noise an MGM wheel-hub motor makes, especially considdering that it's 98% efficient, IIRC. I believe that most air-cooled brushless DC motors would have a similar noise level. There is a clacking noise generated that is load enough to get anoying inside the unshielded body of the Manta GT sloar race car. The stator coils contract slightly when energized becasue the individual windings are attracted to eachother. Most of the motor controller inefficiencis result from its inability to generate perfect square wave outputs. Rise times kill effiency. This means that the input to the coils will be as sharp a feasably possible, whcih means that the contraction of a coil will probably produce an audible "clack" if there is no insulating medium (such as liquid coolant ductwork) between the listener and the coil. When I first heard it, I thought there was a piece of plastic in contact with the rotor because it sounded like a playing card clacking on a bike spoke. Granted, an electric motor will be quieter than a comparable IC engine, especially an unmuffled nitromethane engine with racing cams. Don't be fooled into thinking that electric cars are necessarily silent, though.
About the constant-torque issue: it is true that most brushless DC motors develop nearly constant torque over thier entire RPM range. However, this is sub-optimal. The near constant torque arises from constant clearance between the rotor and the stator coils. The maximum RPM is also determined by the back-EMF, which is affected greatly by the rotor clearance. There is an optimum clearance for a given set of operating paramiters, so many of the more advanced motors have an actuator that moves the stator back and forth in order to continually optimize the rotor clearance for efficiency. So it actually turns out that the optimum torque curve decreases with RPM. Right now, however, manually adding shims to the motor controls rotor clearance more accurately than an actuator that adjusts clearance dynamically. Since most of the time durring solar car races is spent on highways, cruising right at the speed limit, it's most efficient for the MIT Manta GT to have the rotor clearnce set for cruising speed by dissasembling the motor in lab and adding or removing shims. The extra efficiency gained at cruising speed more than makes up for the inability to continuosly optimize the motor.
On a side note, don't assume that exotic processes and materials are better. Take for instance, the University of Michigan's solar car frame is made of titanium. (At least a few years ago it was.) Titanium is light weight, but very difficult to work with. Titanium is notoriusly expensive and comparitively expensive to work with. It is also imposible to design Titanium for an infinite fatigue life. (The maximum vibration allowable amplitude asymptotically aproaches zero as designed fatigue life approaches infinity. For most steels, however, the allowable amplitude asymptotically appraoches a positive value. Trust me, I spent an entire semster at MIT learning about crack growth and fatigue.) I'm told that the University of Michigan's Ti frame weighed only seven pounds less than the MIT ChroMolly steel frame. Which is more reliable? Which cost less? How many pounds are you willing to shave at eh cost of money and reliability?
Karl
Karl
I'm a slacker? You're the one who waited until now to just sit arround.
Copyright Violation:"theft, piracy"::Anti-Trust Violation:"thermonuclear price terrorism"<-Overly dramatic language.
Public transportation may not be the best solution for some cases, people will still want their cars to drive wherever they want. But trains and subways do have their own advantages. Have you tried to read or sleep as you drive your car every day to and from work? I compare the transportation problem to computers. Public transportation is like a big mainframe. People want to have a personal computer on their desks, but mainframes are still the best solution to many tasks. We need a well planned, well integrated, public transport network, which we will use on a day to day basis. We also need roads and cars, for special trips, like what we do on weekends, for instance.
The reason why public transportation systems have been so neglected is mainly a question of bad pricing regulation. You don't need to explicitly pay anything to drive on public roads and streets. You do need to pay to ride on trains. This makes roads and streets seem to have a much lower cost than they really do. A well planned transportation policy should get rid of this subsidized personal transportation policy and make people pay the real cost for the use of cars and trucks over public roadways.