5 ms·

The flywheels are interesting to me, especially for their use in vehicles. I wonder what the tests for catastrophic failure looked like though, especially since

by jjcm 9y ago

The flywheels are interesting to me, especially for their use in vehicles. I wonder what the tests for catastrophic failure looked like though, especially since that Volvo engine spun theirs at 60,000rpm max. That is a lot of energy in a small package.

jaggederest 9y ago
Interestingly, most of the energy in a moving automobile is actually stored as angular momentum in the drivetrain components, rather than what you might intuitively expect as linear kinetic energy in the mass of the frame, for example.
- tfolbrecht 9y ago
  That is extremely weird considering the frame etc has so much more mass. Do you have some math on that?
  - TheSpiceIsLife 9y ago
    I would expect this to be true only below a certain speed given a certain vehicle mass. It's obviously incorrect at 100 mile an hour with the engine idling and in neutral.
    - robotresearcher 9y ago
      You seem to be ignoring the wheels. Lots of angular momentum there.
  - jaggederest 9y ago
    I just know the math indirectly, from observing that stopping distances scale linearly with rolling component mass but by the square root of the total mass of the vehicle. Relevant to modifying vehicles - if you put larger, heavier rims on your car, you must also upgrade the braking system or you're rendering it unsafe to drive by possibly doubling the stopping distances.
    - taneq 9y ago
      The number I've read is saving 1kg of rotating mass is equal to saving 4kg of chassis weight. I can't believe rotating components make up 1/5th of a car's mass though.
      - TheSpiceIsLife 9y ago
        That's got to be averaged out over all rotation mass in the vehicle though right? The shaft to a CV joint is going to have a helluva lot less angular momentum than a wheel.
        taneq 9y ago
        It was a rule of thumb from a drag racing website so it's probably highly biased towards wheels. I think they did mention lightening the flywheel on the engine too, though - although that's best thought of as energy storage, rather than energy loss, since you reclaim the energy in the flywheel at the next gear change.
mjevans 9y ago
The failure mode of bulk energy storage (battery/fuel/etc) will almost surely be worse; and at least with flywheels once it pops it's done.
Theodores 9y ago
Williams F1 did the most recent relevant work on flywheel energy storage for F1 KERS Kinetic Energy Recovery Systems. They dropped it from the original F1 application in preference to the batteries that the other F1 teams were using. A few Porache 911 GT3 cars were modified to use the flywheel. These track only cars didn't have a passenger seat, instead the flywheel was there, spinning round at tens of thousands of revolutions per minute, just next to your 'privates'. More recently Le Mans cars have had the flywheel although nowadays the business is owned by GKN. Williams sold the business after it was not found to be what they needed for F1. Lots of London busses have the flywheel, it has found its application in stopping busses and getting them back up to speed quickly. How much power does the flywheel give out? The peak power is about 3/5 of a Nissan Leaf. It is designed to be used in series with the main engine or in parallel. In this way the vehicle can be designed to have a much smaller engine with the flywheel taking care of all acceleration. Multiple flywheels can be used. The applications the flywheel is sold into are specialist where things get serviced properly. I don't think it will ever be in mainstream automotive because we are giving up on ICE cars and if you have got batteries on the car anyway then you might as well use them for the regen. Now where I think Williams went wrong was in not making a flywheel that happened to be made from some lithium-ion batteries. So that metric tonne of batteries lugged around on a Tesla, imagine how much potential energy you could store if you flew that around at 36k RPM. You could spin the thing up before leaving the house and not have to use the battery for your first few miles. I would like to see a purely mechanical version of flywheel, so just gears and a clutch to transfer energy to the flywheel when braking and accelerating away.
- slilo 9y ago
  Reminds me on gyrobus https://en.wikipedia.org/wiki/Gyrobus https://en.wikipedia.org/wiki/Gyrobus "A gyrobus is an electric bus that uses flywheel energy storage, not overhead wires like a trolleybus."
  - robotresearcher 9y ago
    Reminds you? It is completely explicit! > Lots of London busses have the flywheel, it has found its application in stopping busses and getting them back up to speed quickly.
wmeredith 9y ago
Eh, lots of energy in a small package is kind of the point. You know, like a tank of gasoline :) A catastrophic failure of that is also quite bad, but we mitigate it and live with it due to the advantages provided.

by jjcm 9y ago

jaggederest 9y ago

Interestingly, most of the energy in a moving automobile is actually stored as angular momentum in the drivetrain components, rather than what you might intuitively expect as linear kinetic energy in the mass of the frame, for example.

tfolbrecht 9y ago
That is extremely weird considering the frame etc has so much more mass. Do you have some math on that?
- TheSpiceIsLife 9y ago
  I would expect this to be true only below a certain speed given a certain vehicle mass. It's obviously incorrect at 100 mile an hour with the engine idling and in neutral.
  - robotresearcher 9y ago
    You seem to be ignoring the wheels. Lots of angular momentum there.
- jaggederest 9y ago
  I just know the math indirectly, from observing that stopping distances scale linearly with rolling component mass but by the square root of the total mass of the vehicle. Relevant to modifying vehicles - if you put larger, heavier rims on your car, you must also upgrade the braking system or you're rendering it unsafe to drive by possibly doubling the stopping distances.
  - taneq 9y ago
    The number I've read is saving 1kg of rotating mass is equal to saving 4kg of chassis weight. I can't believe rotating components make up 1/5th of a car's mass though.
    - TheSpiceIsLife 9y ago
      That's got to be averaged out over all rotation mass in the vehicle though right? The shaft to a CV joint is going to have a helluva lot less angular momentum than a wheel.
      - taneq 9y ago
        It was a rule of thumb from a drag racing website so it's probably highly biased towards wheels. I think they did mention lightening the flywheel on the engine too, though - although that's best thought of as energy storage, rather than energy loss, since you reclaim the energy in the flywheel at the next gear change.

mjevans 9y ago

The failure mode of bulk energy storage (battery/fuel/etc) will almost surely be worse; and at least with flywheels once it pops it's done.

Theodores 9y ago

Williams F1 did the most recent relevant work on flywheel energy storage for F1 KERS Kinetic Energy Recovery Systems. They dropped it from the original F1 application in preference to the batteries that the other F1 teams were using. A few Porache 911 GT3 cars were modified to use the flywheel. These track only cars didn't have a passenger seat, instead the flywheel was there, spinning round at tens of thousands of revolutions per minute, just next to your 'privates'. More recently Le Mans cars have had the flywheel although nowadays the business is owned by GKN. Williams sold the business after it was not found to be what they needed for F1. Lots of London busses have the flywheel, it has found its application in stopping busses and getting them back up to speed quickly. How much power does the flywheel give out? The peak power is about 3/5 of a Nissan Leaf. It is designed to be used in series with the main engine or in parallel. In this way the vehicle can be designed to have a much smaller engine with the flywheel taking care of all acceleration. Multiple flywheels can be used. The applications the flywheel is sold into are specialist where things get serviced properly. I don't think it will ever be in mainstream automotive because we are giving up on ICE cars and if you have got batteries on the car anyway then you might as well use them for the regen. Now where I think Williams went wrong was in not making a flywheel that happened to be made from some lithium-ion batteries. So that metric tonne of batteries lugged around on a Tesla, imagine how much potential energy you could store if you flew that around at 36k RPM. You could spin the thing up before leaving the house and not have to use the battery for your first few miles. I would like to see a purely mechanical version of flywheel, so just gears and a clutch to transfer energy to the flywheel when braking and accelerating away.

slilo 9y ago
Reminds me on gyrobus https://en.wikipedia.org/wiki/Gyrobus https://en.wikipedia.org/wiki/Gyrobus "A gyrobus is an electric bus that uses flywheel energy storage, not overhead wires like a trolleybus."
- robotresearcher 9y ago
  Reminds you? It is completely explicit! > Lots of London busses have the flywheel, it has found its application in stopping busses and getting them back up to speed quickly.

wmeredith 9y ago

Eh, lots of energy in a small package is kind of the point. You know, like a tank of gasoline :) A catastrophic failure of that is also quite bad, but we mitigate it and live with it due to the advantages provided.