# Releasing mechanical energy over time

1. Feb 2, 2012

### greyd927

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?

2. Feb 2, 2012

### Staff: Mentor

You mean like in a watch? Yes...

3. Feb 2, 2012

### greyd927

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

Last edited: Feb 2, 2012
4. Feb 3, 2012

### gsal

Well, how are you planning on using such mechanical energy? what does your load look like?

5. Feb 3, 2012

### nasu

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.

6. Feb 3, 2012

7. Feb 3, 2012

Damper?

8. Feb 3, 2012

### James_Harford

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.

9. Feb 3, 2012

### James_Harford

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.

10. Feb 4, 2012

### James_Harford

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_(device)

11. Feb 16, 2012

### greyd927

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?

Last edited: Feb 16, 2012
12. Feb 16, 2012

### Drakkith

Staff Emeritus
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.

13. Feb 16, 2012

### QuantumPion

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

14. Feb 16, 2012

### greyd927

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.

15. Feb 16, 2012

### Drakkith

Staff Emeritus
How long do you want to store the power before using it?

16. Feb 16, 2012

### greyd927

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.

17. Feb 16, 2012

### Drakkith

Staff Emeritus
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.

18. Feb 16, 2012

### greyd927

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.

19. Feb 16, 2012

### Drakkith

Staff Emeritus
Well, now you have me confused. What's wrong with normal batteries? I thought you wanted to store it for much longer than a month or two. Batteries would work great for storage in this manner.

20. Feb 16, 2012

### greyd927

A spring or coil can be rewound over and over again whiteout the need for external electricity. Batteries only have one use or require existing electricity to recharge them.

And if i wanted to store it for a day the design could easily be changed to store it for a few months or even a year. Potential energy is pretty easy to store. A day is just a really simple easy interval to start out with.