JESSE
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elastic energy storage???
Anyone have any leads on a high efficency system for storing large amounts of elastic and or knetic energy????
Weight and capacity are a factor.
 
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12AX7
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Carbon fiber is probably the best bet, although I don't know how it would hold up under repeated stress.
Elastic energy storage is a really bad idea unless you need a very fast impulse (the mechanical equivalent of capacitors, making a catapult or
ballista analogous to a railgun) or short, repeated absorption (e.g., damping springs).
And though you make absolutely no mention of your education, I'm guessing from your posting style that you don't know a damned thing about kinematics.
Read a mechanical physics textbook and understand the concepts of force, displacement, velocity, acceleration, spring constant, tension, compression,
and a whole lot of other things that matter.
Tim
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vulture
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Hmm, I was under the impression that carbon fiber was rather rigid and not very elastic?
Do you have any mechanical parameter data of carbon fiber, tim? I'd be very interested. Carbon tends to be tricky in its mechanical properties, you
could very well be right.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Fleaker
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As Tim mentioned, storage of elastic energy is not ideal because to be efficient and useful it needs to all be released at once.
I know they make composites with carbon fiber that vary greatly on the medium, resin-bonded carbon fiber is very stiff and is very rigid, while there
are types of high temperature/strength ropes made out of it.
Tricky indeed.
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Magpie
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Tim, I never realized that the stored enegy in a spring must be realeased at once to be efficient. A spring stores energy as (kX^2)/2 if IRC.
Wouldn't the most efficient release be a reversible (hence very slow) release?
Tongue-in-cheek: Springs could be shipped to countries with dirt cheap labor where they could be manually compressed. These would then be sent back
to countries with prohibitively high rates such as the US and Europe where the stored energy could re released as needed. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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12AX7
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The thing about slow release is, you may not need much power, but energy goes up with time and it can quickly pile up for long times. Springs don't
store much energy compared to other devices.
Consider a truck spring of say, 2000lbs for one foot compression ~= 1 tonne force = 10kN per 1/3 meter so k = 30kN/m, E = 1/2 kx^2 = E = 1/2 * 30k *
1/9 = 10k/6ths, uh 1.67kJ. A lead-acid battery of similar size might be a car battery, which is around 40 amp-hours charge capacity and 13.8V
nominal. 40 amp-hours is 60*60*40 coulombs, which even as low as 12V is 1.73 megajoules. Even with these horrendous ballpark estimates, it
just doesn't compare!
(A 9-volt battery might be in the range of 300mAh, 9V = 9.7kJ, enough to squash a U.S. quarter, if you transfer the charge to a device capable of
releasing it in ten microseconds!)
I don't know the entropy of any typical chemical reactions, or how you could represent it in terms anyone here will understand. It seems to me no one
here deals much with energy quantitatively, so it's a moot point anyway. Examples such as batteries and car springs are much more physical, and the
average person has probably seen these items.
So, about springs. E = 1/2kx^2 so E goes up with k: a stiffer spring holds more energy. It also goes up with x (or theta, if you have an angular
spring), so a longer spring also holds more energy. That doesn't say much about size, though. For this you need to include bulk properties such as
modulus of elasticity and maximum (yield) tensile strength. I'm not a mechanical engineer unfortunately, but it seems to me you don't necessarily
want an incredibly stiff nor highly flexible material. More like, the product of tensile strength and modulus.
The thing about steel is, it's very strong. A common alloy such as 1080 (plain high carbon steel), heat treated properly, starts taking a permanent
bend (i.e., compression energy is taken by deforming the metal- bad) around, say, 100,000 PSI. I don't know how that corresponds to say, bending or
torsional forces, which are used more often in springs. A common alloy with very high strength is 4340, circa 250KSI (KSI = "k PSI"), but I don't
know how it fares as a spring. Modulus for pretty much all steel alloys is around 30.7M PSI = 212GPa (for 4340).
Then there's the superalloys, like inconel, stellite, hastelloy and so on. I don't remember offhand which is strongest.
These are all about the same density, specific gravity = 8 or so. If your goal is to save space, not weight, these are just fine. If you need to be
as light as possible, you can proportionally sacrifice flexibility or strength for density. This is why aluminum, with a third the stiffness, half
the strength and third the density of steel, rules aircraft. You also get the added bonus, where stiffness is concerned, that for the same weight,
thickness of a given piece can be doubled, which means stiffness is quadrupled! That's the other reason aluminum is used.
(Titanium has half the density of steel, but the same strength. It has some ups and downs, like being ten times more expensive than aluminum and
sensitive to tearing (titanium bolts need rounded shanks and threads!), but it's used in a lot, too.)
Now, composites, like fiberglass, carbon fiber, foam and so on, are very flexible, but they are also very, very light compared to anything else. You
need more volume or width or whatever to make up for the stiffness, but you get a hell of a lot more strength in the process!
Generally, since a structure has to endure loads with a deflection and weight spec, and since carbon fiber is at the top of stiffness vs. weight vs.
deflection, I think it might be a good starting point for energy storage. I might be wrong on that, and for sure it depends on just what kind of
energy storage you're looking for, but that's my thought.
FYI, if you must have a mechanical form of energy storage, mass holds a lot more energy than a spring. If linear motion isn't possible, a spinning
drum might do it.
Magpie: there's nothing unreversible about, e.g., a catapult firing. It would be a rather useless contraption if you couldn't crank it back for
another shot 
Tim
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Magpie
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Tim I'm refering to thermodynamic reversibility where you are trying to prevent the loss of energy to heat.
The single most important condition for a successful synthesis is good mixing - Nicodem
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12AX7
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Well an ideal spring only stores energy (linear force vs. displacement, i.e., constant k). An imperfect spring absorbs some percent of the energy (a
non-restorative force). No heat involved, in a perfect spring, and no time scale of concern (E = kx^2 is energy, not power).
A perfect spring connected to a perfect mass (no loss due to shaking, no drag, etc.) will oscillate forever as the energy is transferred back and
forth from kinetic energy to potential (spring force) energy.
Tim
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bullstrode
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Maybe JESSE will specifiy what quantity of energy he would like to store and over what period he would like to release it, or was the homework
question not that detailed? There are various practical implementations of elastic energy stores such as crossbows and watch-springs. For kinetic
stores there are various kinds such as projectiles and flywheels; flywheels can be very efficient.
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franklyn
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Solid State Heat Engine
It is incongruous to me that a physical effect that by the late 1970's received much interest
has since, for the most part, been relegated to becoming an obscure laboratory curiosity.
This despite having contemporary usefulness in medical devices such as vascular stents and
compression couplings for joining aircraft fuel lines, even linear actuators _
http://www.migamotors.com
and electrically energized "muscle wires" for walking robots.
http://media.wiley.com/product_data/excerpt/83/08186740/0818...
But its most intriguing application as a soild state heat engine remains as yet unexploited aside
from its initial investigation and some experimental research.
http://stinet.dtic.mil/oai/oai?&verb=getRecord&metad...
Certain metal alloys in their solid state exhibit a transition between two distinct crystalline
phases that changes their physical dimension in response to crossing a preset temperature,
for the earlier known ones typically on the order of 2 to 3 %. These are termed shape memory
alloys. With the introduction of NiTinol, an alloy of Nickel and Titanium, dimensional change
occurs up to a potential maximum of 7%, putting it in a mechanically advantages range. The
alloy is softer more malleable in the martensite crystal phase which occurs below the transition
temperature. When heated incrementally only 2 or 3 degress above its transition temperature
the alloy extremely abruptly alters its physical state and shape into austenite crystalline
structure which exhibits much higher tensil strength and temper. The temperature at which
this change will occur is predetermined by the precise percentage of the two elements that
comprise this alloy. http://en.wikipedia.org/wiki/Shape_memory_alloy
http://www.stanford.edu/~richlin1/sma/sma.html
http://pergatory.mit.edu/medical/mitral/documents/Analysis/C...
In its simplest form, a single loop of this alloy wire strung around two pulleys, one having a
diameter slightly greater than the other, is all that embodies a working engine. Placing the
wider pulley on your left with the axles pointing toward you, the lower portion of the assembly
is submerged in a cooling water bath which maintains the soft martensite crystalline phase.
The upper portion of the assembly may be subjected to localized heating which induces the
austenite crystalline phase. The result of this is that due to the leverage of the wider wheel
as the upper length of the wire loop shrinks it pulls and causes the entire unit to rotate
clockwise, since the lower portion of the wire loop having less tensil strength, gets stretched.
Though small, even demonstration models are capable of producing considerable torque and
moderate speed up to 2 or 3 hundred revolutions per minute. Termed Pulley engines see
depictions on pg.19 of the following *.pdf here _
http://scholar.lib.vt.edu/theses/available/etd-09252002-1707...
Various other designs have been originated by imaginative inventors. One such using fixed
lengths of wire connecting two crankahafts can be seen in operation in this *.mpg.
http://scholar.lib.vt.edu/theses/available/etd-09252002-1707...
In this case the heat is provided to the lower portion by a heated bath and cooling by the
fan seen at the left. See all of these video links on page 56 of the *pdf cited above.
another reference
[ Nitinol-wire engines, Scientific American's THE AMATEUR SCIENTIST 1986 May, pg 124 ]
The function of another type used in educational demonstrations is explained here _
http://groups.physics.umn.edu/demo/thermo/4F3060.html
http://www.physics.montana.edu/demonstrations/apparatus/4_th...
http://faraday.physics.uiowa.edu/heat/4F30.60.htm
and can be seen in operation here _
http://faraday.physics.uiowa.edu/Movies/MPEG/4f30.60.mpg
It has been noted that the latent heat energy present in the temperature differential
between the surface and the depths of a moderately deep body of water such as lake
Meade behind Hoover Dam, is seven times that of the gravitational head. That means that
if you drained the lake for electrical generation you will have thrown away seven times
as much energy as it produced flowing through the turbines. The problem with harnessing
such a potential resource has always been that it was considered to be at an entropic low
from which it was not recoverable, until discovery of solid state heat engine technology.
Contemporary cost escalation of conventional energy resources presents a challenge
that merits considering development of this all but forgotten application which although
it has only 4 o 5 percent conversion efficiency the energy available for it is all around in
abundance. http://pdf.aiaa.org/jaPreview/JE/1978/PVJAPRE47980.pdf
http://www.winstonbrill.com/bril001/html/article_index/artic...
Problems to overcome
http://www2b.abc.net.au/science/k2/stn/archives/archive98/ne...
In depth technical assessment
http://www.wpi.edu/Pubs/ETD/Available/etd-021606-104515/unre...
If you're comfortable with engineering software here is a calculator to predict performance.
http://www.smaterial.com/SMA/simulation/vers2/sma-sim_site.h...
U P D A T E _ 07/04/24
Metal structure for shape memory identified _
http://www.whatsnextnetwork.com/technology/index.php/2007/04...
.
[Edited on 24-4-2007 by franklyn]
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Maya
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a high speed circular spinning weight holds the most stored kinetic energy
alternatively
to convert the energy from electricity you could use a HV rail gun or coil gun
\"Prefiero ser yo extranjero en otras patrias, a serlo en la mia\"
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Twospoons
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I was working for a company involved in industrial sized UPS systems. The energy storage was in a 10kg epoxy composite flywheel spinning at 40,000
rpm. This gave a storage of 3MJ. Energy was transferred in and out via a long, thin brushless DC motor that ran up the centre of the flywheel ( max
transfer rate of 300kW !). The biggest hurdle was getting bearings to stand up to that kind of punishment. At the time, high speed ceramic (SiC)
bearings on flexible mounts were being used. I never saw the thing go past 20,000 rpm because the bearings would shit themselves. Alignment and
balance were absolutely crucial.
The flywheel was wrapped in carbon fibre to stop it flying to bits, and running in a vacuum chamber to stop it melting due to air friction! 
So mech storage is possible, but not always trivial.
Helicopter: "helico" -> spiral, "pter" -> with wings
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franklyn
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| Quote: | Originally posted by Twospoons
energy storage was in a 10kg epoxy composite flywheel spinning at 40,000 rpm.
This gave a storage of 3MJ. Energy was transferred in and out via a long, thin
brushless DC motor that ran up the centre of the flywheel ( max transfer rate of 300kW !). |
I beleive that got a write up in Popular Science magazine many years ago. As it
happens a homopolar motor although bigger retains more energy in self inductance
so it need not run as fast.
| Quote: | Originally posted by Twospoons
The biggest hurdle was getting bearings to stand up to that kind of punishment. At the
time, high speed ceramic (SiC) bearings on flexible mounts were being used. I never saw
the thing go past 20,000 rpm because the bearings would shit themselves. Alignment and
balance were absolutely crucial. |
Full floating bearings used by turbosuperchargers are good out to 150,000rpm
and then some, but there is a drag penalty. Magnetic bearings can do better.
The unexpected problem with this type of system is the precession of the disk
flywheel, any ambient vibration sets it into a wobble hence the bearing wear.
.
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12AX7
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"precession"
Hell, what of the day-to-day rotation of the Earth? With that much mass (depending on its plane, of course), you ought to be able to detect the
yearly rotation, too!
Tim
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gregxy
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Titanium is a good material. It has a very high yield strength and low modulous of elasticity as compared to other metals.
I don't know how it compares to materials like carbon fiber or rubber.
The best energy storage systems are chemical, like a gasoline engine for slow release or an explosive like TNT for
fast release. The main drawback is chemical based systems are not reversable.
Pneumatic based storage can also be a good choice if multiple high energy pulses are needed.
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12AX7
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Well, if you want high power density, electric is the way to go (think Z machine). High energy density comes from chemical fuels, or better still (if
harder to obtain ), nuclear fission or fusion.
Tim
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franklyn
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| Quote: | Originally posted by 12AX7
"precession"
Hell, what of the day-to-day rotation of the Earth? With that much mass (depending on its plane, of course), you ought to be able to detect the
yearly rotation, too! |
I do not refer to diurnal variance which is a coriolis effect only relevant in gyroscopes of inertial navigation devices.
I own a compact very high speed verticle drill press made with the sort of construction
then common in the 1950's, quite hefty and well finished, powered by a universal motor
it can get up to 12 - 13000 rpm. The chuck only accepts stems of less than 3/16 thick
and is intended for use with dental end mills and drills the size of a tailor's straight pin.
Fool that I am, I thought I could use this as an improvised turret mill with a full size saw.
The disk saw is slightly over 2 inches in diameter. I rigged a stem for it and set it perfectly
balanced in the drill's chuck. I intended to slice some height off a hard plastic cylynder.
Slid on the drill's table rest I had no more than merely touched the plastic to the saw and
B A N G , instantaneously the chuck with saw materialized on a 90 degree elbow bent in
the shaft, making one half turn to a dead stop. I managed to bend the drills 5/16 shaft
back to straight again but it was not an easy task and the perfection of the elbow bend
has remained memorable.
.
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