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Releasing mechanical energy over time

by greyd927
Tags: energy, mechanical, slow, spring, time
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greyd927
#1
Feb2-12, 09:50 PM
P: 25
Is there a way to wind up a spring or coil to store mechanical energy and then release that energy slowly over a longer period of time instead of allowing the spring to release rapidly all at once?
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russ_watters
#2
Feb2-12, 10:14 PM
Mentor
P: 22,234
You mean like in a watch? Yes...
greyd927
#3
Feb2-12, 10:16 PM
P: 25
But a watch releases the energy in spurts, the second hand for example repeatedly moves forward and pauses. I'm looking for a more constant motion

gsal
#4
Feb3-12, 05:30 AM
P: 872
Releasing mechanical energy over time

Well, how are you planning on using such mechanical energy? what does your load look like?
nasu
#5
Feb3-12, 08:38 AM
P: 1,969
How about the (old) spring toys? You coil the spring (usually a spiral one) with a key and then the toy moves quite continuously until the spring is relaxed. The newer models have no key but you turn the spring by pulling them backwards over a surface.
QuantumPion
#6
Feb3-12, 03:13 PM
P: 766
You can use a dashpot.
fonz
#7
Feb3-12, 03:35 PM
P: 79
Damper?
James_Harford
#8
Feb3-12, 10:10 PM
P: 67
Quote Quote by greyd927 View Post
But a watch releases the energy in spurts, the second hand for example repeatedly moves forward and pauses. I'm looking for a more constant motion
Start with the axle of the second-hand of a watch or windup clock. It solves very nicely the problem of delivering a constant average flow of energy, but it is delivered in bursts. What is needed is something that averages or smooths the delivery of that energy.

Attach one end of a long elastic rod to the second-hand axle and the other end to the axle of the drive wheel of the machine to which the energy is to be delivered. Suppose the drive wheel is locked and cannot turn. Then energy is delivered by the axle of the second hand to the rod which twists until the torque applied to the rod is equal and opposite to the torque applied by the rod to the second-hand axle. At this point, the rod contains potential energy.

When the drive wheel is unlocked, the potential energy is smoothly delivered by the rod to the drive wheel of the machine and is replenished by the "ticks" of the second hand axle. The energy flow to the machine can be made as smooth a you like by increasing the torsional elasticity of the rod.
James_Harford
#9
Feb3-12, 10:21 PM
P: 67
Quote Quote by QuantumPion View Post
You can use a dashpot.
Using viscous friction will smooth motion, but waste energy by converting much of it into heat. What is needed is an energy efficient solution. Relying on the internal friction of a wound-up-spring toy to regulate energy is much like using a dashpot.
James_Harford
#10
Feb4-12, 09:10 AM
P: 67
Quote Quote by James_Harford View Post
Start with the axle of the second-hand of a watch or windup clock.
A far better solution than the one I provided is to use a mechanical governor as described in this article:

http://en.wikipedia.org/wiki/Governor_%28device%29
greyd927
#11
Feb16-12, 12:06 AM
P: 25
The elastic rod idea is interesting but I feel as if the constant stretching and relaxing of the relaxing of the elastic would eat up more energy and eventually warp the elastic. I hadn't thought of a governor though, that would be a pretty good idea.

I want to create a mechanical battery of sorts. Modern day batteries are getting more and more efficient but can only store the energy for a fixed period of time. While I don't need to produce a lot of energy I would like to store it mechanically in order to store it for a much much longer period of time then modern batteries allow.

This does not necessarily have to be a spring, but any from of mechanical / potential energy which I can easily convert to electricity quickly and smoothly.

I would most likely use this mechanical energy to move a magnet past a coil (doesn't get much simpler) but what if i built the magnet right into the governor as the weights for example? I could condense the design and possibly even prevent one energy loss.

thoughts on how such a design could be done?
Drakkith
#12
Feb16-12, 02:11 AM
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Drakkith's Avatar
P: 11,501
How much energy are you wanting to store? I don't think there's a reasonable way to get anywhere close to the energy density of a battery by mechanical means at home AND be able to store it for a long time, so your device would be much larger than reasonable unless you are storing energy equal to about the amount in your standard AA to D size batteries or similar.
QuantumPion
#13
Feb16-12, 12:33 PM
P: 766
Quote Quote by greyd927 View Post
The elastic rod idea is interesting but I feel as if the constant stretching and relaxing of the relaxing of the elastic would eat up more energy and eventually warp the elastic. I hadn't thought of a governor though, that would be a pretty good idea.

I want to create a mechanical battery of sorts. Modern day batteries are getting more and more efficient but can only store the energy for a fixed period of time. While I don't need to produce a lot of energy I would like to store it mechanically in order to store it for a much much longer period of time then modern batteries allow.

This does not necessarily have to be a spring, but any from of mechanical / potential energy which I can easily convert to electricity quickly and smoothly.

I would most likely use this mechanical energy to move a magnet past a coil (doesn't get much simpler) but what if i built the magnet right into the governor as the weights for example? I could condense the design and possibly even prevent one energy loss.

thoughts on how such a design could be done?
There are two major ways to store mechanical energy in use today:

http://en.wikipedia.org/wiki/Flywheel_energy_storage

http://en.wikipedia.org/wiki/Compressed_air_car
greyd927
#14
Feb16-12, 09:04 PM
P: 25
I don't need to store all that much energy, only about 5v. Its a really small amount but it needs to be a constant power output for slightly more than an hour. I could modify the rest of the design for half the time but I would really rather not. I figure releasing mechanical energy from a spring / coil and converting it to create such a small amount of electricity would be simple enough, but its the constant output over time I’m having trouble with.

Now that I'm thinking, I'm not sure if a governor would even fit this situation.
Drakkith
#15
Feb16-12, 09:07 PM
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P: 11,501
How long do you want to store the power before using it?
greyd927
#16
Feb16-12, 09:11 PM
P: 25
If I'm storing it in a spring or a weight i should be able to store it for a very long time, especially if i change the design to use a falling weight, then i could store it indefinitely.
Drakkith
#17
Feb16-12, 09:34 PM
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Quote Quote by greyd927 View Post
If I'm storing it in a spring or a weight i should be able to store it for a very long time, especially if i change the design to use a falling weight, then i could store it indefinitely.
But what is your goal for storage time? Do you have one in mind? I can't see any benefit to long term storage of such a small amount of energy. And remember that mechanical systems are still prone to degradation too.
greyd927
#18
Feb16-12, 09:48 PM
P: 25
lets say i wanted to store it for a day. I wouldn't mind being able to go longer, but a day would be pretty ideal.


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