Catch up on stories from the past week (and beyond) at the Slashdot story archive

 


Forgot your password?
Close
typodupeerror
×
Technology

NYC Subways Testing Flywheels 363

Posted by michael from the next-stop-42nd-street dept.
socolow writes "The New York Times (free registration required) has an article about the NYC subway system's use of flywheels to store the braking energy of trains approaching stations. Not only does this advance the development of flywheel energy storage, but it will help relieve a lot of the heat subways generate (always appreciated during the summer)."
This discussion has been archived. No new comments can be posted.

NYC Subways Testing Flywheels More

NYC Subways Testing Flywheels

Comments Filter:

  • Regenerative braking (Score:2, Insightful)

    by nuggz ( 69912 )
    Why not just use regenerative braking.
    Aren't they already electric?
    It is probaly easier to implement (mechanically) and less additional weight on the subway.
    • Flywheels are (theoretically) more efficient than batteries or fuel cells. IIRC, batteries are 10% efficient, fuel cells 30-40%, while flywheels can be as efficient as the motors (up to 80%).

    • Re:Regenerative braking (Score:3, Interesting)

      by Noofus ( 114264 )
      I think the reason for not using regenerative braking is that it would essentially requirew the flywheel to be ON the train. This isnt necessaraly a bad thing. You could regenerativly brake INTO your on-board flywheel and then use the stored energy to get the train moving again (with a little help from the third rail).

      They may not have wanted to implement it this way because it might have been easier to build a few flywheels into each station rather than build them into every train in the system. Also this way they can get the idea implemented quickly (install flywheels at stations) rather than have to wait many years while the trains get replaced slowly as they wear out and die.
      • Slow down, turbo.

        Fly wheels have one big issue: very low tolerance for movement. A lot of time and money has gone into using flywheels for cars, but the biggest issue was always trying to keep the thing from crashing--it moves so much that it can't be held by the magnetic ball bearings and it touches the side of the container. This is really bad. Not only do you loose a lot of speed, but it increases the chance of an explosion of carbon-fiber.

        Better to make big flywheels that are stationary and burried in a mountain of cement.
    • I believe thats what they are doing, except they are using flywheel batteries to store the electricity generated during braking.

    • Re:Regenerative braking (Score:4, Informative)

      by marauder404 ( 553310 ) <(marauder404) (at) (yahoo.com)> on Tuesday July 30, 2002 @03:08PM (#3980045)
      If you read the article, you'd know: they can't put power right back into the third rail because the resistance of the rail is too high. And they can't put it into batteries because there aren't batteries big enough to solve the problem. So they use a flywheel.

      Please read the article before posting, next time.
      • clue me in please... why is the resistance such a problem, if the third rail is how they are powering the trains in the first place? Why does the braking energy from the trains get wasted, but the energy from the systems that are powering the third rail does not?

        • The third rail is already highly charged. Trying to push power from a battery would be like trying to save on power bills by hooking a 9V battery w/ an AC Adaptor to the wall outlet - there's too much power there to push more back in.

          • 'The third rail' should really be 'The third rails'. No subway system has a single third rail which powers the whole system, they're always broken into short sections.

            I don't see any reason why there can't be an unpowered third rail specifically for returning power at the stations where most of the braking will take place. If for some reason a train gets stuck there, then the power can be turned back on for long enough to get the train into the next section.

          • The third rail is already highly charged. Trying to push power from a battery would be like trying to save on power bills by hooking a 9V battery w/ an AC Adaptor to the wall outlet - there's too much power there to push more back in.

            Yeah, it's almost as ludricrous as putting solar panels on your roof and then trying to sell power back to the grid. Oh wait. [tracegridtie.com]

        • Re:Regenerative braking (Score:5, Informative)

          by Waffle Iron ( 339739 ) on Tuesday July 30, 2002 @04:12PM (#3980606)
          clue me in please... why is the resistance such a problem, if the third rail is how they are powering the trains in the first place? Why does the braking energy from the trains get wasted, but the energy from the systems that are powering the third rail does not?

          IAAEE, so I'll hazard a guess. They say in the article that the 3rd rail uses 650V DC. For power distribution, this is a relatively low voltage. To minimize resistance losses, power is typically distributed at thousands of volts. To be able to easily convert voltages, you need AC, not DC so you can run it through a transformer.

          I'll bet that they have high-voltage AC power distribution throughout the system, and they step it down to 650 V and rectify to DC it at frequent intervals along the tracks. The distance the power needs to run at low voltage along a high-resistance steel rail would never be very long, so losses are minimal. (I assume they use DC becuase it's easier to design train motors for DC, or something like that.)

          The AC -> DC rectification is not reversible, however, so there would be no way for power generated by a train to get back into the main distribution grid, and the average distance the 650V DC would have to flow throught the 3rd rail to the next train would be too far to be economical.

          (Of course, I could be wrong about all of this, since I don't really know anything about their system.)

          • Re:Regenerative braking (Score:5, Informative)

            by candover ( 39486 ) on Tuesday July 30, 2002 @05:21PM (#3981208)
            That's how the system works, yes. The MTA has 214 substations around the city, which are fed something between 11-27 kV AC, transformed to 400 V AC, and rectified to 600 V DC.

            It's only within the last ten years that they finally retired all of the old pre-solid-state rotary converters [nycsubway.org] in the system - running power backwards through them would have actually worked. :)

            The new cars actually have AC motors - the DC third rail powers a battery on board, I'm not sure exactly what the AC conversion tech is. There's still a couple thousand DC-motored cars riding the rails, so I'm not expecting to see the system switch over to AC distribution....

        • Re:Regenerative braking (Score:5, Funny)

          by 4of12 ( 97621 ) on Tuesday July 30, 2002 @04:59PM (#3981032) Homepage Journal

          clue me in please... why is the resistance such a problem, if the third rail is how they are powering the trains in the first place?

          It's all tied together with social security.

          Politicians are often heard saying something along the lines of

          "Social Security is the third rail. Don't touch it."

          You've probably noticed that Social Security benefits are mostly received by old people.

          You've probably also noticed that those old people move slowly. The reason they move more slowly than you or me and the reason they can't drive more than 20 mph under the speed limit is simply because they are encountering resistance.

          Hope that clears it up.

      • Actually, I'm pretty sure that the power is put back into the third rail. The article does not, in fact, say that the resistance in the third rail is always too high. Rather, it says that the resistance is too high if there are no trains close by. After all, resistance is proportional to distance.

        So basically, the plan will be to distribute these flywheel batteries throughout the subway system so that there is always one close by when a car is generating power through its regenerative braking system.

        The author's attempt to simplify the description of the system probably made this hard to see.
    • I'm thinking the batteries aren't that much lighter than a flywheel.

      But one of the biggest reasons not to use the electric motors as generators during breaking to store the power in batteries, is it is probally more efficient to not conver the mechanical energy to electrical, and then when you start rolling again, to turn the stored electrical back to mechanical. Just store the energy as mechanical in the first place.

      On the other hand high energy flywheels are about as scary as wet cell batteries when things go wrong. I saw a video of a Kevlar flywheel coming apart and doing its best to take apart the shield around it.
      • Batteries are heavier. Still, they didn't actually say AFAIK, but I think that they were planning to put the flywheels in the station, not on the train; so the weight doesn't matter much. It may be that the flywheels are cheaper than the batteries, and they only have to store the energy for a short time in this case anyway- so it's a perfect application.

      • If the flywheels are built into the subway stations, they can be more than shielded. They will probably be sealed into massive metal chambers surrounded with concrete. Sure, if one breaks it'll be a huge undertaking to replace, but you won't have lost any efficiency compared to now, and you won't kill people as 100-pound chunks of flywheel go flying at 80MPH.

        And you don't really design a system like this with the intent to have it break down.

        Flywheels won't make it into vehicles for some time, especially cars - there's too many unpredictable problems. You wold have to install self-destructive safety mechanisms in your flywheel to avoid killing people.

        Imagine yourself stopping at a light, and when someone rear-ends you, your flywheel immediately blows itself into dust to save your life. Only your life didn't need saving, and now you need a new car.

    • Re:Regenerative braking (Score:3, Informative)

      by mosch ( 204 )
      They are using regenerative braking. That's what the whole article is about, a new application of regenerative braking in a place that people don't usually associate with relatively new technologies.

    • Re:Regenerative braking (Score:4, Informative)

      by n9hmg ( 548792 ) <n9hmg@hotmaiMENCKENl.com minus author> on Tuesday July 30, 2002 @03:23PM (#3980171) Homepage
      Why not just use regenerative braking
      I'm usually a little kinder than this, but you plainly don't know what regenerative braking actually is. It's a lot more than just a feature of your R/C car. The story is all about regenerative braking. Rather than using friction to convert kinetic energy to heat and getting rid of it, using the motor to convert it back to electrical energy. The flywheels are just the most efficient place to hold on to that energy until it's needed again. It's more efficient to store it near where it's generated, since a stopping train is likely to start again, from the place where it stopped, than to send it all along the system on the rail, where it will mostly be wasted in heating the third rail before it reaches a useful load.
      The thing i found surprising about this story was learning that they weren't already doing something like this.

  • levitrain (Score:4, Funny)

    by Mt._Honkey ( 514673 ) on Tuesday July 30, 2002 @03:01PM (#3979980)
    Now if they just make the flywheel out of a superconductor, then not only will it store energy, but the train will be weightless!!!

    Boeing, get on it!

    • Re:levitrain (Score:3, Funny)

      by Anonymous Coward
      Considering how trains in the US are rarely on time, I'd prefer they be waitless :)

  • Wow - that would take us all the way to 1920! (Score:4, Interesting)

    by sphealey ( 2855 ) on Tuesday July 30, 2002 @03:01PM (#3979981)
    Wow - that would take us all the way to 1920 and the Milwaukee Road's use of regenerative braking on their electrified lines through the Cascade Mountains!

    sPh

  • Gyroscopes (Score:3, Insightful)

    by Maniakes ( 216039 ) on Tuesday July 30, 2002 @03:02PM (#3979987) Journal
    Since the flywheels are just great big gyroscopes, what happens when the train makes a sharp turn?

  • A Wired article (Score:4, Informative)

    by L. VeGas ( 580015 ) on Tuesday July 30, 2002 @03:03PM (#3979998) Homepage Journal
    Wired [wired.com] ran an article about the new flywheels [wired.com] a while ago.
    • ...spin a flywheel 20 times faster, at 100,000 rpm, producing 400 times the centrifugal force.

      Silly journalist....there is no such thing as centrifugal force.

      Centripital. Yes.

      Oh how I love rotating bodies.

  • Pros and Cons (Score:4, Funny)

    by teamhasnoi ( 554944 ) <teamhasnoi AT yahoo DOT com> on Tuesday July 30, 2002 @03:04PM (#3980004) Journal
    Every seat will have a little crank to turn to help drive the flywheel.

    Unfortunately, it takes 45 minutes of winding for 4-5 seconds of run time.

  • Before the visit ended the other day, a final question had to be asked: What is the purpose of the floating ping-pong ball?

    "Oh that?" Mr. Lobenstein smiled like a child. "That's just to amuse us. Sometimes we get bored."
    • I liked this one more, concerning putting the excess joules right back into the rail:

      "The only problem is that when the power goes back into the rail, it is quickly eaten up by the resistance of the metal. So if other trains are not close by, to scoop up the power, the extra electricity dissipates like so many ripples in a pool."

      If other trains are not close by? How close do they want trains to be?

      That quip about the heat in the stations is no joke. If you go to the yellow line (N/R/Q/W) stations, it is like 110 deg F down there minimum, at 2 AM! People stagger around down there panting and sweating like they're Ozzy.

      • If you've ridden on the NYC subway system, you'd know that the trains can be VERY close to each other. But that's not the point...

        This system is essentially giant battery (or rather, 10 small ones) in every station to suck up the power put back into the rail by trains stopping at that station. If a train slows down far away from another train or station battery, there's not much good that power being pumped back into the rails are gonna do anyone.

        Oh, by the way. The reason that the resistance is such a problem? They're DC motors. That's why they can be REVERSED and used as generators. You can't do that with alternators/AC motors. For reasons why DC has problems with transmission across long conductors, ask your local Slashdot geek about the "war" between Edison and Tesla.
      • Yes, but the trains have AC, so its nice and cool, then the doors open, and its 110 degrees blast of air. Doors Close and its nice and chilled again. Real problem to using trains, the heat.

  • I don't buy it (Score:5, Funny)

    by L. VeGas ( 580015 ) on Tuesday July 30, 2002 @03:09PM (#3980054) Homepage Journal
    I still think my hamster could spin a wheel faster than some dumb fly.

  • Heat due to A/C (Score:3, Interesting)

    by yasth ( 203461 ) on Tuesday July 30, 2002 @03:16PM (#3980103) Homepage Journal
    Hmmm the heat has little to do with the electric motors, and much more to do with Air Conditioned Subway cars. The heat in the cars has to go somewhere so it (and some energy involved in moving it) goes out into the tunnels and the stations. Suposedly before A/C the cars were hot but the stations were cool(as one would expect for what is bassicaly a basement.)
    • 600M Watts is what the system uses, thats a crapload of power. I am guessing total efficiency of the system for actually moving people is like 20%, that means the heat from 480M watts of wasted electricity is given off into the subway system, quite a bit. I just got back from vacation and my brain is still mostly off or I would compute how many BTU's.

  • Where to stick your flywheel.... (Score:5, Informative)

    by Sweetums ( 266193 ) on Tuesday July 30, 2002 @03:16PM (#3980105)
    Several posts refer to the flywheel as being on the train. I don't think it explicitly says in the article, but I think it's clear that they are talking about stationary equipment in the stations, not flywheels on the trains. Lots of advantages to this.

    The modifications to the trains are actually significant to support this, but it's about how the braking systems work and how the motor controllers work on the trains. There are a class of motor controllers that are not really compatible with regenerative braking, and they are fairly commonly used since they are cheaper than the others. The conversion to regenerative braking may involve replacing a fair bit of gear on the rolling stock. They were considering this kind of thing in San Diego, which is where I picked up lots of this trivia.

    Many rail systems and streetcar systems have regenerative braking, but frequently they don't store the energy. What they do is have one unit braking while another is accellerating, so the excess power is in effect transferred via the wire to the other vehicle. Think of cable car systems where the guy at the top of the hill counterbalances the one at the bottom. This is hard to make work though, the timing issues being what they are.

    My $.02

    • I wouldn't say the article does an exceptional job of describing where the flywheels are placed, but a closed read does imply very strongly that they are outside.

      Besides, 10 batteries, each the weight of a Volkswagen, might have some negative impact on the performance characteristics and power usage of your average subway train.
  • From the out_of_the_topic dept.

    If you dont wanna register at NYTimes visit NYT Random Login Generator [majcher.com]
    But because NYTimes block based on referrers you got two chances 1 - Disable Javascript or a better one get Multizilla Toolbar for Mozilla [mozdev.org]
    It has a nice option like "Dont send referrer" .
    Choose it and boom you are in !

  • A little too excited? (Score:3, Funny)

    by dr_dank ( 472072 ) on Tuesday July 30, 2002 @03:18PM (#3980127) Homepage Journal
    Or, as Robert Schmitt, another transit electrical official, put it, excitedly: "They're sitting here, saying: `Give it to me! Give it to me! Give it to me!'

    Ok, this guy needs to get laid. Now.
  • "it will help relieve a lot of the heat subways generate (always appreciated during the summer)."

    Now, if they could just do something about the smell. The Broadway-Fulton-Nassau station certainly gets rank in the summer.

  • Wow, 36,000 is a lot of RPM... (Score:5, Informative)

    by dpbsmith ( 263124 ) on Tuesday July 30, 2002 @03:22PM (#3980166) Homepage
    and a million watts is a lot of power.

    Let's hope those flywheels are enclosed in something pretty solid.

    Storing that much energy is one thing. Accidentally releasing it is another. When I was a student at MIT there was a permanent display in a glass case in the hallway of the biology department showing a centrifuge rotor that exploded, just to remind everyone of what happens when something spins too fast.

    Let's also hope there's something to muffle that 600 Hz whine (which is close to the peak of human hearing sensitivity).

    And I thought the wheels on Boston's Green Line screeching when going around sharp turns was bad...
    • Last I heard, high-performance flywheels were being made of graphite fibre... spin 'em too fast and the fibres separate, dissapating the energy (and turning your very expensive flywheel into a box of cotton candy).
      • But that cotton candy still contains all the energy that was stored in the flywheel, and that energy has to go somewhere.

        A flywheel's mode of failure is catastrophic. A failure in a set of flywheels that stored a *megawatt* of power is going to kill a lot of people unless it is properly contained.
    • http://web.mit.edu/charliew/www/centrifuge.html

    • Re:Wow, 36,000 is a lot of RPM... (Score:5, Informative)

      by aeoo ( 568706 ) on Tuesday July 30, 2002 @03:59PM (#3980486) Journal
      Actually, modern flywheels are almost never solid. They are usually made from rings, or fiber. There is a Russian scientist named Gulia who invented and patented (to my knowledge) a way to wind fiber so that both ends end up inside the flywheel. This is critical because at high RPM a loose end can undo the entire flywheel. Using kevlar and other fiber like that allows you to have flywheels that can withstand incredible forces. In general, flywheels are far more efficient than any battery in terms of energy storage, and how fast they can store and release energy. Also, modern flywheels can fly on a magnetic suspension and in vacuum as well. Flywheels, in my opinion, are simply the best way to store energy. When fiber flywheel explodes, it does so one thread at a time. They are relatively safe and the only thing they generate when they explode is heat.
      • 10 inch diameter 25 pound carbon fiber flywheel at 36,000 rpm.

        Edge speed is 1071 Miles per hour.

        A "flander" is a large splinter that explodes off the inside of a ship's hull when a cannon ball hits broadside at sub-sonic velocities. Thus the term "smash to flanders".

        a 25 pound cannonball will completely breach 8 inches of wood creating a manticore of wood splinter shrapnel.

        A tornado will drive pieces of straw through a wall at subsonic speeds.

        A winch cable will crack at supersonic speeds if it snaps. A winch cable will shear an engine block.

        100 lashes is a death penalty.

        Kinetic Energy = 1/2*I*w*w

        I = moment of inertia --> ability of an object to resist changes in its rotational velocity

        w = rotational velocity (rpm)

        I = k *M*R*R (M=mass; R=Radius); k = intertial constant (depends on shape)

        Inertial constants for different shapes:

        Wheel loaded at rim (bicycle tire): k =1
        solid disk of uniform thickness; k = 1/2

        I assumed 4/5 because of the design they used

        Kinetic Energy of flywheel = 68,428,800 Joules

        357 Magnum = 937 Joules .50 cal sniper rifle = 16,539 Joules

        4000 sniper rifle bullets worth of energy exploding outward in the form of tiny splinters of a substance that happens to have one of the highest tensile strengths. Assume 98% of the kinetic energy is lost to heat. 80 sniper bullets.

        Bad news.

    • I work with pro audio, and let me clue you in on the range of human hearing...

      We can hear as low as 20hz and as high as 20,000hz (20k). However, most people perceive stuff above 16k as some sort of noise, but they can't really make it out or get a directional location on it.

      The human voice has a smaller range... around 85hz for a really good male bass singer up to 1.1k for a really good female soprano.

      That's not the whole of it though, because you get into things about even/odd harmonics, plus the fact that one octave around 20hz doesn't take many additional cycles to hit the next octave, but it takes thousands of cycles around 20k to jump an octave.

      Human hearing isn't linear by any means. We are nearly deaf at the lower end of the scale; that's why we often "feel" bass -- not because when its loud enough to hear it is also felt, but more like to get enough energy so that our ears can even hear it you have to put out a LOT of power. But I digress...
  • Related to this is the Parry People Mover [parrytech.com] which has been developed by a small company in Wales. This is designed as a light urban tansit system using flywheel to run the "people movers". The flywheels in these lightweight cars are recharged by either onboard LPG internal combustion engines or by electric motors fed from recharging points at stations.

    They have been trialed on the Welsh Highland Railway [bangor.ac.uk] and on the island of Mauritius [railway-technology.com] omngst several other schemes - a quick Google search [google.com] will turn up a lot more information about some of the trials.

    While not a total success it is good to see innovation in this area.

  • More information here (Score:5, Informative)

    by brandonsr ( 550431 ) on Tuesday July 30, 2002 @03:25PM (#3980184) Homepage
    Right here [powerpulse.net] A very good article (with illustrations) that tells how flywheels work and store energy. Pretty neat stuff.
  • What about the homeless people who rely on the subway heat vents in the winter?
    • Well, maybe the next time the cops offer them a spot at the shelter, they won't turn it down. Police and social services go out every night and round up the homeless so they don't freeze to death. Some of the homeless prefer a subway grate to the shelters and if they're not obviously nuts, the police have to let them do it. 1/3 of the homeless population is mentally ill.

    • It's illegal to be homeless in New York City.

      Don't believe me? Want to mod me down? Go ahead, just don't try to not have a job or a home or any money in NY, otherwise they'll throw you in jail.
  • I personally love the idea of using flywheels to store energy in this manner -- it seems very elegant to simply transfer the energy into rotational motion, rather than simply losing it all as heat.

    There's one safety concern I have that I haven't yet seen addressed, though I've probably just missed it. If a flywheel is spinning at several tens of thousands of RPM (such as the 36,000 RPM flywheel mentioned in the story), what happens if the flywheel's physical supports are damaged or destroyed?

    Basically, let's say a truck crashes into the building storing a spinning flywheel. The flywheel's housing is hit and breaks, putting the flywheel into physical contact with other materials. What happens? I have visions of a thousand-kilo ceramic disc either spinning off like the Tazmanian Devil, leaving a disc-shaped cartoon hole in whatever it encounters, or shattering upon impact and spraying shards of material at hundreds of meters per second in sundry directions.

    The problem is, I don't know if this is actually true or not. Can anyone with an actual knowledge of such things answer? Thanks.
    • Actually, I already had one idea for avoiding this (potential) problem... if the flywheels are rotating around an axis perpendicular to the ground, then you can place the flywheel in a pit dug into the ground. That way, if the flywheel "crashes" or spins off, it will (in theory) embed itself a few meters into solid rock. Seems better than having it above-ground, anyway.
    • Shrugs, these are underground. And there arn't that many earthquakes in NY, (though some are predicted) I assume they have figured most of this out already.
    • They are carbon fibre so they disintigrate, though the immediate surroundings may take some punishment. That is why they are usually entoumbed in several feet of concrete.
  • I used flywheel technology many years ago with my Hot Wheels Destuction Alley Playset(TM). The flywheels would drive the cars at unpossible! speeds.

    Of course, I don't recommend loop the loops, and the CrossRoads of Danger(TM) would have to go.

    The cool cardboard desert backgrounds and grandstands could stay, though. And the orange plastic track would make an excellent subway defense weapon!

    "Mom, he's beating me with the track again!" "Well, hit him back, I'm busy!"

  • A good break down of Power vs. Energy located here [afstrinity.com] . Not here [ucsofa.com].

  • nycsubway (Score:2, Interesting)

    by nycsubway ( 79012 )

    I love the NYC Subway system. It smells bad at times, but its an engineering marvel. So many people, tunnels, electrical, mechanical systems. a good website is http://www.nycsubway.org [nycsubway.org]

  • Jumbo Capacitor (Score:2, Interesting)

    by dnoyeb ( 547705 )
    Effectively this is like a big capacitor. I surmise a chemical battery would have issues with constant discharge/recharge. Whereas a flywheel couldn't care less.

    The flywheels could not go in the train because the bumpy ride would continuously siphon off power, and you know power siphoned off would be in the form of heat. Not to mention that each battery weighs as a small volkswagen :D

    Their solution to the voltage loss in the 3rd rail is a half-assed one. They claim the distance between the trains would cause too much loss in the line if they tried to transmit power back across it. Yet they are still transmiting power across it anyway?!? They must plan on the average distange between a train and the battery station to be smaller than between a train and another train, though the article strangely failed to say.

    I really didnt enjoy 1/2 the article being fluff about the lack of glory in being a transit engineer...
  • Here [slashdot.org] is an article describing some early testing of flywheels and how dangerous they can be in the wrong hands. Please take care when experimenting with flywheels.

    They'll put your eye out.

  • Braking power? (Score:2, Insightful)

    by ldopa1 ( 465624 )
    I understand the concept of harvesting braking to push a flywheel to greater speeds, therefore storing the energy, but I have a couple of questions:

    Aren't flywheels tremendously heavy? Wouldn't the additional weight cause longer stopping distances, especially under emergency braking?

    I do understand that the braking would be assisted by the flywheel itself (spinning it up), but you never get anything for free (See The First Law of Thermodynamics [maricopa.edu].). When spinning up the wheels, you'd have heat loss, and loss again when they are spun down. Secondly, again, because of the 1st Law, wouldn't the heat generated by all of those flywheels spinning up and down exactly equal the heat savings? Moreover, thinking of emergency braking - What is the top speed of the flywheels? How strong do the gears need to be to spin up the flywheel to top speed very quickly? And at what tremendous gear ratio?

    Don't think that I'm against it, cause I'm not. I think the electricity savings alone make it worth the effort and expense, but I'm not convinced that the trains would be as safe as the existing ones, and that there would be any heat savings. That said, CA needs to convert the BART next....

    • Re:Braking power? (Score:2, Interesting)

      by boarder ( 41071 )
      the wheels aren't on the trains, they are on the tracks. yes, putting heavy wheels on the train would increase stopping distances, but these are ground fixed and change the translational motion of the train to rotational motion. because of friction and other losses, the energy isn't completely transfered, but it's better than nothing. the way this will help braking is that the brakes won't have to work so hard on the trains themselves so it will help emergency braking (IF it is near one... there will only be a certain number of them spread throughout the grid).

      Of course, I didn't read the article so I may be wrong... but I've read a lot of posts and this is what they are saying.
    • Yes, you don't get back out exactly what was put in, but it does make the system more efficient and saving $20 million a year in electric costs is nothing to sneeze at. Nothing wrong with making the system a bit more efficient, helps both the environment and the city at the same time.
  • The article says that the chief electricians were able to get a ping-pong ball to levitate!

    Has anyone told Boeing yet? [slashdot.org]
  • ...to the conservation bomb [technologyreview.com].
  • Most of the warmth in the subways is caused by heat that has been absorbed by the roadbeds above radiating downward into the stations, to a lesser degree by the exhaust of the air conditioning on subway cars, and to a still smaller degree by steam tunnels that border some of the tunnels and run in parallel conduits. Not by braking trains.
  • Considering this confused statement:

    A very, very big battery. Or, to be more accurate, 10 of them, each weighing as much as a Volkswagen Bug and together able to store up to a million watts of power.

    Are we to take this article seriously, or to believe anything it says? If they do not know the difference between power and energy, there is no telling what else in the article may be untrue.

  • a few years ago (Score:2, Interesting)

    by KingPrad ( 518495 )
    I remember Discover magazine doing an article about a scientist named Bitterly workeing for US Flywheel Systems developing flywheel technology for use in cars. At that time he had developed a way to make superdense flywheels from (I think) carbon thread spun into solid rings. It was extremely rigid and dense and maintained shape for a long time and at high (1700) rpm.

    Each flywheel gave steady 25 horespower and could double that for short kicks. Four would drive a car, but you could fit about 16 in an engine compartment (don't need engine, transmission, etc). That's 400 horsepower, and if you floor it you get 800 instantly! Also they would take you about 300 miles on a spin-up, which was accomplished by plugging the car into a wall socket, revving up the wheels with an electric motor - a charge would cost about 6 dollars of electricity.

    Flywheels are better than batteries in a lot of ways. I'm glad to see they are finally being used for commercial applications. I haven't heard anything about the automobile flywheel guy since, but I'm sure his work won't be for nought. I'm equally sure car manufacturers and oil companies would stop him flat if he tried to market it though.

    http://www.discover.com/search/index.html

    You can search for it here with 'flywheel' as keyword - article name is 'Reinventing the Wheel'.

Slashdot Top Deals

It is easier to write an incorrect program than understand a correct one.

Close