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#1
08-18-2012, 04:38 AM
 AaronX Guest Join Date: Feb 2011
Is there any mechanism to accelerate a flywheel with no max speed?

Hypothetical situation: I have a free source of energy, like a rotating drive, piston or moving water. I want to store this in a flywheel. The amount of energy I can store is limited by the max speed of the flywheel. But if I use, say, gears, the max speed is determined by the max gear ratio. Is there any mechanism with no max speed?

I was thinking if the energy source were a jet of air, I could use a turbine, and maybe change the angle of the blades as it sped up, but the speed would be limited when the speed of the air equalled the speed of the surface of the blades, no?
#2
08-18-2012, 05:16 AM
 coremelt Guest Join Date: Jan 2009
AFAIK, most flywheel systems use gear-less electric motors and the limitation is the strength of the material on how fast it can spin before it shatters, not how fast the electric motor can spin the flywheel.
#3
08-18-2012, 05:21 AM
 si_blakely Guest Join Date: Jul 2002
I think you are right.

The most flexible coupling will be electromagnetic - you can vary the frequency of the external field to transfer energy to the flywheel from v. low to extremely high. Quite what the maximum is, I don't know - some function of the collapsing magnetic field, and I expect efficiency to fall off. You also have electrical efficiency losses as you vary the frequency. However, you gain the ability to extract energy from the flywheel at any rate of rotation and without physical coupling.

Si
#4
08-18-2012, 05:24 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by AaronX I was thinking if the energy source were a jet of air, I could use a turbine, and maybe change the angle of the blades as it sped up, but the speed would be limited when the speed of the air equalled the speed of the surface of the blades, no?
Not necessarily - or else sailing faster than the wind would not be possible.
#5
08-18-2012, 08:18 AM
 AaronX Guest Join Date: Feb 2011
Yes I know flywheels use electrical motors, I was wondering if this was possible mechanically?
#6
08-18-2012, 08:48 AM
 Francis Vaughan Guest Join Date: Sep 2009
With air you will be in trouble when the ends of the blades exceed the speed of sound - this isn't a hard limit, but things will start to get weird at this point, and your efficiency will drop off.

A turbine with moving blade angles is really no different to a gearbox, indeed you are not that far from how an automatic gearbox works, albeit using a gas instead of a liquid.

Whatever system you use to spin the flywheel up, you need a symmetric system to get the energy out again efficiently. Normally you would want to use the input system in reverse.
#7
08-18-2012, 11:23 AM
 astro Member Join Date: Jul 1999 Location: Taint of creation Posts: 28,348
As others have pointed out the physical material the spinning flywheel is composed of will be self (probably explosively) destructing way before the gearing mechanism or support spindles etc. get stressed to their breakdown points.
#8
08-18-2012, 06:48 PM
 Hail Ants Charter Member Join Date: Jan 2000 Location: NY USA Posts: 4,556
Just for laughs-

Just as the tips of aircraft propellers should not be allowed to exceed the speed of sound, the edge of any spinning disc cannot exceed the speed of light. Some quick (probably wrong) math later and:

The edge of a 6 inch disc would approach the speed of light at approximately 3,127,650,000 rpm give or take.

I doubt even any hypothetical bucky-ball-admantium-unobtanium disc could approach this speed. I'm not even going to consider that as it spun up the outer parts would approach c sooner than the inner parts and would appear to slow down in time whilst the inner would speed up- brain hurts....

Last edited by Hail Ants; 08-18-2012 at 06:50 PM.
#9
08-18-2012, 07:21 PM
 Little Nemo Charter Member Join Date: Dec 1999 Location: Western New York Posts: 47,855
Quote:
 Originally Posted by astro As others have pointed out the physical material the spinning flywheel is composed of will be self (probably explosively) destructing way before the gearing mechanism or support spindles etc. get stressed to their breakdown points.
I think it was the great engineer W.B. Yeats who once said, "Turning and turning in the widening gyre...Things fall apart; the centre cannot hold."
#10
08-18-2012, 07:53 PM
 astro Member Join Date: Jul 1999 Location: Taint of creation Posts: 28,348
Even a pretty tough material like the polycarbonate of CDs is not immune to g forces

See Compact Disc shattering
#11
08-20-2012, 10:15 AM
 Chronos Charter Member Join Date: Jan 2000 Location: The Land of Cleves Posts: 47,925
Quote:
 Just as the tips of aircraft propellers should not be allowed to exceed the speed of sound, the edge of any spinning disc cannot exceed the speed of light.
True, but it's not a problem, since in that span where you're approaching the speed of light, you've got enough room for an unlimited amount of kinetic energy.
#12
08-20-2012, 02:09 PM
 Der Trihs Member Join Date: Aug 2005 Location: California Posts: 33,610
Quote:
 Originally Posted by astro As others have pointed out the physical material the spinning flywheel is composed of will be self (probably explosively) destructing way before the gearing mechanism or support spindles etc. get stressed to their breakdown points.
So use a rotating black hole instead; they can be spun up to near lightspeed. I'm not sure if that counts as a "flywheel" though.
#13
08-20-2012, 02:25 PM
 Sunspace Charter Member Join Date: Jun 1999 Location: Back in the GT eeehhhh... Posts: 24,940
I think the limiting factor for solid substances would be the radial tensile strength of the spinning flywheel as it continually has to keep those parts of itself near the rim of the disc in a circular orbit.
Quote:
 Originally Posted by Der Trihs So use a rotating black hole instead; they can be spun up to near lightspeed. I'm not sure if that counts as a "flywheel" though.
And it it has an electrical or magnetic charge on it, you can couple to it for acceleration and deceleration! Or am I understanding that wrong?
#14
08-20-2012, 02:28 PM
 Sunspace Charter Member Join Date: Jun 1999 Location: Back in the GT eeehhhh... Posts: 24,940
Quote:
 Originally Posted by Hail Ants The edge of a 6 inch disc would approach the speed of light at approximately 3,127,650,000 rpm give or take. I doubt even any hypothetical bucky-ball-admantium-unobtanium disc could approach this speed. I'm not even going to consider that as it spun up the outer parts would approach c sooner than the inner parts and would appear to slow down in time whilst the inner would speed up- brain hurts....
Well, what would happen as the edge of a spinning disc approached lightspeed?
#15
08-20-2012, 09:43 PM
 Chronos Charter Member Join Date: Jan 2000 Location: The Land of Cleves Posts: 47,925
Sunspace, you're not understanding that wrong. Although putting a magnetic charge on a black hole does present some practical challenges...
#16
08-20-2012, 09:51 PM
 Leo Bloom Member Join Date: Jun 2009 Posts: 4,515
Quote:
 Originally Posted by Little Nemo I think it was the great engineer W.B. Yeats who once said, "Turning and turning in the widening gyre...Things fall apart; the centre cannot hold."
Excellent.
#17
08-20-2012, 10:09 PM
 HoneyBadgerDC Guest Join Date: Jul 2012
Quote:
 Originally Posted by AaronX The amount of energy I can store is limited by the max speed of the flywheel. But if I use, say, gears, the max speed is determined by the max gear ratio. Is there any mechanism with no max speed??
This is not exactly right

The amount of energy you store in a flywheel is a product of both the center of mass in the flywheel and the speed of the flywheel, you determine roughly how much energy you want to store at a reasonable speed and then simply add enough weight to the flywheel to give you the energy figure.
#18
08-20-2012, 10:52 PM
 AaronX Guest Join Date: Feb 2011
Actually I was wondering if anyone had invented a gear set with a ratio 1 : infinity, or something similar, more than the practical aspects of it. So would a gas jet and a turbine have a maximum speed for the turbine? Maybe if the nozzle could be adjusted so the speed of the jet changed?
#19
08-20-2012, 11:09 PM
 Little Nemo Charter Member Join Date: Dec 1999 Location: Western New York Posts: 47,855
Quote:
 Originally Posted by badger5149 The amount of energy you store in a flywheel is a product of both the center of mass in the flywheel and the speed of the flywheel, you determine roughly how much energy you want to store at a reasonable speed and then simply add enough weight to the flywheel to give you the energy figure.
That leads to a theoretical possibility. Suppose you could design a flywheel that always moves at a constant speed? But you could add energy to the flywheel by increasing its mass. Double the mass at a constant speed and you've doubled the energy. And you could presumably withdraw energy by the same means - remove mass while keeping the rotation at a constant speed.

It's obviously a theoretical system - I don't know how you'd add and subtract mass from a constantly rotating object. But if you could build it, you'd avoid some of the problems of the variable speed flywheel. No light speed concerns anyway.
#20
08-20-2012, 11:11 PM
 HoneyBadgerDC Guest Join Date: Jul 2012
Quote:
 Originally Posted by AaronX Actually I was wondering if anyone had invented a gear set with a ratio 1 : infinity, or something similar, more than the practical aspects of it. So would a gas jet and a turbine have a maximum speed for the turbine? Maybe if the nozzle could be adjusted so the speed of the jet changed?
Even if you had a flywheel that could reach the speed of light without comming apart, the amount of energy needed to run it would be sucked out long before reaching that speed. I don't think Niagra Falls would have nearly enough power to spin a small toyota flywheel anywhere near the speed of light.
#21
08-21-2012, 12:30 AM
 kyogi Guest Join Date: Jul 2012
Quote:
 Originally Posted by AaronX Hypothetical situation: I have a free source of energy, like a rotating drive, piston or moving water. I want to store this in a flywheel. The amount of energy I can store is limited by the max speed of the flywheel. But if I use, say, gears, the max speed is determined by the max gear ratio. Is there any mechanism with no max speed? I was thinking if the energy source were a jet of air, I could use a turbine, and maybe change the angle of the blades as it sped up, but the speed would be limited when the speed of the air equalled the speed of the surface of the blades, no?
If I correctly grasp the gist of the question, my answer is this: think magnetic suspension in place of a spindle.
#22
08-21-2012, 12:49 AM
 HoneyBadgerDC Guest Join Date: Jul 2012
Quote:
 Originally Posted by Little Nemo That leads to a theoretical possibility. Suppose you could design a flywheel that always moves at a constant speed? But you could add energy to the flywheel by increasing its mass. Double the mass at a constant speed and you've doubled the energy. And you could presumably withdraw energy by the same means - remove mass while keeping the rotation at a constant speed. It's obviously a theoretical system - I don't know how you'd add and subtract mass from a constantly rotating object. But if you could build it, you'd avoid some of the problems of the variable speed flywheel. No light speed concerns anyway.
By moving the center of mass on a rotating flywheel it would have the same effect as adding mass. It would require more energy to maintain the speed and conversely store more kinetic energy.

If the poster is speaking of energy storage as he stated he made one very important wrong statement. He feels the energy storage is limited by the speed of the flywheel, it is more limited by the mass of the flywheel. Or mass and speed.
I hear this logic all the time when guys think putting bigger tires or higher geared trans will speed up their cars top end. You simply cant get any more power out than what you put in.
#23
08-21-2012, 01:03 AM
 kyogi Guest Join Date: Jul 2012
Badger, you're spot on, but I was taking a pot shot at the true intent of the OP question. Wasn't bothering with details until some OP feedback. When that comes, we may, twixt us, have a real answer for him. Which is kinda depressing, because as this thread continues, I find more & more to think about that I haven't in years.
#24
08-21-2012, 02:02 AM
 AaronX Guest Join Date: Feb 2011
Actually I'm wondering more about transmissions than flywheels. Another way to phrase the question might be: can you get an infinite gear ratio with a finite number of gears (and no electrical motors)?
#25
08-21-2012, 02:16 AM
 kyogi Guest Join Date: Jul 2012
Quote:
 Originally Posted by AaronX Actually I'm wondering more about transmissions than flywheels. Another way to phrase the question might be: can you get an infinite gear ratio with a finite number of gears (and no electrical motors)?
OK. That's a different game. Gonna go have a smoke & think about that.
#26
08-21-2012, 02:38 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by AaronX Actually I'm wondering more about transmissions than flywheels. Another way to phrase the question might be: can you get an infinite gear ratio with a finite number of gears (and no electrical motors)?
The answer is no. Apart from maybe exotic things like black holes, there isn't anything physical/real that scales from finite to infinite. Infinite isn't a synonym for 'very large'.
#27
08-21-2012, 02:46 AM
 AaronX Guest Join Date: Feb 2011
I don't know. That's what I would have said about an infinite number of gear ratios, until I heard about CVT.
#28
08-21-2012, 03:26 AM
 Princhester Charter Member Join Date: Jan 2001 Location: Brisbane, Australia Posts: 10,500
Quote:
 Originally Posted by AaronX I don't know. That's what I would have said about an infinite number of gear ratios, until I heard about CVT.
No you are confusing an infinite number of ratios with an infinite range of ratios. A theoretical perfect CVT is infinitely variable within its maximum and minimum ratios, but does not have an infinite range.
#29
08-21-2012, 07:37 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
You can't have something that is real, starts with a measurable value, then increases to infinity. There is no numeric amount you can add to X to increase it to infinity.
#30
08-21-2012, 08:08 AM
 AaronX Guest Join Date: Feb 2011
How about conductivity of a superconductor?
#31
08-21-2012, 08:15 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by AaronX How about conductivity of a superconductor?
'Infinite conductivity' doesn't mean anything.

A superconductor has zero resistance, or I suppose you could say it's 100% conductive.
#32
08-21-2012, 11:09 AM
 HoneyBadgerDC Guest Join Date: Jul 2012
I don't think that infinite and ratio belong in the same sentence. Several false asumptions in the OP need to be addressed as they are the basis for the question.
If you were to attach air nozzles to a spinning flywheel that would spin it using thrust the flywheel could never attain the speed of the air comming out of the nozzles, the more nozzles you added the closer it would get or the lighter you made the flywheel the faster it would go but no combination would bring it to the speed of the air comming out of the nozzles, or blowing across blades regardless of pitch on the blades.
#33
08-21-2012, 01:50 PM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by badger5149 If you were to attach air nozzles to a spinning flywheel that would spin it using thrust the flywheel could never attain the speed of the air comming out of the nozzles, the more nozzles you added the closer it would get or the lighter you made the flywheel the faster it would go but no combination would bring it to the speed of the air comming out of the nozzles, or blowing across blades regardless of pitch on the blades.
This is incorrect for fan-type turbine - the physics here is that of the inclined plane, which is itself a machine, where mechanical advantage can increase speed. A yacht can sail faster than the wind, and a turbine can move faster than the jets of air driving it, for the same reasons in both cases.

What you say is true for a Pelton Wheel turbine - where the vanes have a cup on the end, and the jets squirt into the cups in the same plane as that of rotation.
#34
08-21-2012, 01:57 PM
 Half Man Half Wit Guest Join Date: Jun 2007
Quote:
 Originally Posted by Der Trihs So use a rotating black hole instead; they can be spun up to near lightspeed. I'm not sure if that counts as a "flywheel" though.
Actually, you can overspin a black hole: the location of the horizon is determined by the ratio of the BH's mass to its angular momentum; eventually, when the angular momentum gets too large, there won't be any horizon anymore, leaving you instead with a naked singularity. Though maybe that'll still work as a flywheel...
#35
08-21-2012, 02:01 PM
 Quercus Guest Join Date: Dec 2000
Quote:
 Originally Posted by Mangetout You can't have something that is real, starts with a measurable value, then increases to infinity. There is no numeric amount you can add to X to increase it to infinity.
But you can have something that is real, starts with a measurable value, and can increase past whatever measure you can come up with. Which is a pretty good rigorous description of infinity, in my book.

So I don't think asking whether a physical thing can go to infinity is meaningless or ridiculous. I mean, for instance, the answer to 'how fast can a shadow move?' is "it's only limited by how strong your light source is and how big a thing you have to cast a shadow on" which can be summarized as 'Infinitely fast'.
#36
08-21-2012, 02:07 PM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by Quercus But you can have something that is real, starts with a measurable value, and can increase past whatever measure you can come up with. Which is a pretty good rigorous description of infinity, in my book. So I don't think asking whether a physical thing can go to infinity is meaningless or ridiculous. I mean, for instance, the answer to 'how fast can a shadow move?' is "it's only limited by how strong your light source is and how big a thing you have to cast a shadow on" which can be summarized as 'Infinitely fast'.
That's just another way of saying "there's no such thing as the biggest number" - it's not the same as finite things being able to transition to infinite.
#37
08-21-2012, 08:37 PM
 AaronX Guest Join Date: Feb 2011
Quote:
 Originally Posted by Mangetout 'Infinite conductivity' doesn't mean anything. A superconductor has zero resistance, or I suppose you could say it's 100% conductive.
You say infinite conductivity doesn't mean anything, yet zero resistance does? In any case, that proves you can start from a finite conductivity reach infinity. So I'll just ask: can I get a gear ratio of 1:0 or 1:epsilon, epsilon arbitrarily small?
#38
08-22-2012, 02:06 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by AaronX You say infinite conductivity doesn't mean anything, yet zero resistance does?
Yes. In the same sort of way that a cup can be empty or full, but not infinitely empty or infinitely full.

Quote:
 In any case, that proves you can start from a finite conductivity reach infinity.
No, it doesn't. That's the opposite of what I said. You can't progress a finite value to infinity (at least not in finite time) - a population of rabbits that doubles every week will get really big, but will never become infinite in any finite period of time.

Quote:
 So I'll just ask: can I get a gear ratio of 1:0
For zero turns of the input shaft, you want the output shaft to turn once. Obviously not - this is similar to the problems encountered if you try to divide by zero.

Quote:
 or 1:epsilon, epsilon arbitrarily small?
There are physical limits to what will actually work, but if you're ignoring physics and talking mathematics only then yes; for any given gear ratio, you can devise another ratio that is higher or lower (proof: just couple two of them together).
#39
08-22-2012, 07:34 AM
 Quercus Guest Join Date: Dec 2000
Quote:
 Originally Posted by Mangetout That's just another way of saying "there's no such thing as the biggest number" - it's not the same as finite things being able to transition to infinite.
Well, I think we're getting to the point where I have to ask "What do you mean by infinite?", you'll wave your hands and say "You know, infinite, forever, without limit" and I say "But I just gave an example of something without limit, and you said that wasn't what you meant by infinite." then you say "OK, scratch the without limit part" and I say "Then what do you mean?" then you say "Infinite!" and I say "So you define 'infinite' as that thing which no finite number can ever reach by increasing?" and you say "Sure" then I say "But that makes your statement kind of boring true by definition, right?" and around here someone derails the thread by talking about how Cantor was crazy; there can't be more than one infinity, and things are never resolved.

There, did I save us both some time?
#40
08-22-2012, 07:41 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 47,505
Quote:
 Originally Posted by Quercus There, did I save us both some time?
Not really, because the question here is not "is there any such thing as a valid concept of infinity?", but rather: "can I actually make or design something with an attribute that is infinite, by just making that attribute bigger or something?"

Last edited by Mangetout; 08-22-2012 at 07:41 AM.

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