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# Power Spring Design?

## Power Spring Design?

(OP)
I am working on a spiral spring powered dynamo system. Where a dynamo is driven by spiral spring through gears.

I am new to the spring design and need help in designing. Does anyone know how to design a spring that could store 100 kilo Joule of energy? The energy stored in the spring will then be used to drive a gear box which in turn drives the dynamo motor connected to it.

Also, please suggest the type of spiral spring that could be used, the best website/book/software that could be used for spiral spring design.

Thanks a lot

### RE: Power Spring Design?

That seems like a lot of energy.

That's about 1kg lifted straight up 10,000 meters, if the metric conversions are working right.

### RE: Power Spring Design?

3DDave is correct :

1 j = 1 N*m
1 kJ = 1000 J = 1000 N*m
100 kJ = 100*1000 N*m = 10'000 kg*m approx

### RE: Power Spring Design?

Some spring manufacturers I have worked with in the past: Century Spring, Associated Spring, SPEC Spring, Lee Spring.

### RE: Power Spring Design?

Sachin Anchan,

You are just going to have to learn how to do this. Your 100kJ is stored in your spring as strain energy, E=δF/2.

You need to select material, design a spring, and test your design for stored energy, yield stress and metal fatigue. If it does not work (and it won't), you need to tweak your design and try again. I agree with the others that 100kJ will be a challenge. I think you will wind up with a weird shape.

--
JHG

### RE: Power Spring Design?

And, if it gets away from you, you may find yourself pushing up daisies.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Power Spring Design?

It's on the order of 100 times as much energy as an automotive suspension spring will store, and those need to be handled with caution when compressed.

### RE: Power Spring Design?

(OP)
I agree the energy stored in the too high.

Jboggs: Thanks for the list, I'll contact them.

byrdj: Thanks for the link, I am looking for detailed flat spiral power spring design, please suggest me formulas/books/software that I can refer while designing.

drawoh: Is there a paper/formulas that I can refer to design a flat spiral power spring which uses all the design aspects that you are suggesting.

In detail description on spring design:

I am working on a flat spiral spring powered dynamo system. Where a dynamo is driven by spiral spring through gears. The spring needs to provide a constant torque of 1 Nm for 3 hours.

Can someone please suggest design formulas that can be used to design such spring.

Thanks a lot guys, you have really provided lot of suggestions.

Regards

### RE: Power Spring Design?

As long as it doesn't unwind a spring can provide that torque forever.

We are back to how much energy you want to store.

### RE: Power Spring Design?

(OP)
3DDave: The energy stored in the spring needs to be equal to provide 1Nm of torque for 3 hours while unwinding.

### RE: Power Spring Design?

Yes, but how many rpm?

1 rpm is a lot different to 100

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Power Spring Design?

(OP)
LittleInch: Thanks a lot for quick reply, rpm=1.

### RE: Power Spring Design?

(OP)
GregLocock: Thank you! My initial design needed 100kJ. For the current design looking for 1Nm torque at 1rpm for 3 hours. Please let me know if you can help me on spring design.

Regards

### RE: Power Spring Design?

(OP)
moon161: Thanks a ton! I owe you one. This is the perfect answer.

### RE: Power Spring Design?

Thanks, Sachin, glad I could help. Machinery's handbook just says 'go to the manufacturer' for spiral springs. Obviously, you'll have to use guesses and converge on the various parameters that get you what you need. As a starting point, because you need near constant force that your initial displacement should be 10X (1800 turns) or more your working displacement (180 turns), and design so you go from 5% over your 3 NM to 5% under as it unwinds.

Andy

### RE: Power Spring Design?

Sachin Anchan,

If you are going to design stuff like this, you need a copy of Roark's Equations for Stress and Strain. Other than that, I suggest you pull out your mechanics of materials texts and read up on strain energy. This is how complex beams are solved, even when they are not springs.

A handy tip, especially given the safety warnings above: When you assemble your mechanism, your spring should be compressed by a screw or a nut, not by hand. When I do this, I make studs long enough that I can install the clamping nut by hand, even though I will need a wrench to do the actual compression.

--
JHG

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