Releasing mechanical energy over time

[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?

 

[russ_watters]

You mean like in a watch? Yes...

 

[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

 

[gsal]

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

 

[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.

 

[QuantumPion]

You can use a dashpot.

 

[fonz]

Damper?

 

[James_Harford]

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]

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]

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_(device)

 

[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?

 

[Drakkith]

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]

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]

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]

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

 

[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.

 

[Drakkith]

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]

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.

 

[Drakkith]

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.

 

[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.

 

[jim hardy]

none of my business - just a thought that wanted out...


my '49 Buick clock used a pull spring about 3 inches long that got re-stretched by an electromagnet every fifteen minutes or so.

Going opposite direction - take apart one of those "Shake" flashlights and experiment with its magnet-coil-supercapacitor ? A mousetrap could yank the magnet through the coil to charge your capacitor after years of waiting.

I don't know how much voltage shake-flashlights make, or whether it'll deliver the current you need.

 

[greyd927]

Thats the general idea I'm going for- stored mechanical energy converted to electric, the problem is something like your mouse trap example would provide energy for just a brief moment where i would need constant power output for about an hour :/

 

[Drakkith]

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.

True, but you are wanting to convert your potential into electrical energy anyways, and it's pretty much all the same components on the electrical side. Whatever is winding your spring could easily be made to generate electricity to charge a battery.

But in the end it's your idea. I don't want to discourage you, I just don't want you to do a lot of unneccessary work. There are plenty of other options. Flywheels, weights, water storage, etc.

 

[greyd927]

The idea is to be able to have on demand power for small devices dispute power outages and what not hence why mechanical energy is my approach

 

[Drakkith]

The idea is to be able to have on demand power for small devices dispute power outages and what not hence why mechanical energy is my approach

If you are converting the power to electrical power anyways, why would storing the energy mechanically be your approach? Batteries are smaller, lighter, can hold more energy, and are generally more reliable. You don't need external electricity to charge them, as whatever you are doing to generate the mechanical energy can easily be used to charge the battery.

 

[zoobyshoe]

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.

As soon as you start 'tapping' the electricity the magnet becomes harder to move relative to the coil. Lenz's Law. Because of this you might figure out a way to have your generator be it's own governor.

If you extended the shaft of a conventional generator, wound a rope around it, lead the rope up to a pulley, and fastened a big weight onto the other end of the rope, as soon as you put a 'load' on the generator (plugged something in) the generator would become harder to turn, and the weight would descend more slowly. Because of what you're trying to design, that could work to your advantage.

You said all you wanted was to generate 5v, but its really the watts you want that makes a difference. 5 volts at how many amps? If you are looking for 5 volts at milliamps, it sounds completely reasonable and doable to me. If you want 5 volts at one amp, it becomes that much less reasonable, and so on. If you know exactly the thing you want to power you can get the watts and design your weight powered generator for that.