Gearbox Springs

[MajorLandmark]

Hey guys.

What Im wanting to know is how springy certain springs are... I dont have any upgrade springs to hand to test them. I mean of course, in terms of N/m or N/mm

Springs I'd like to know about - M100 and 1J. I have a stock TM one that ill be testing soonish, so Ill post up the results in case anyone is interested.
In terms of N/mm I would expect the result to be between 1 and 10N/mm ... anything substantially more or less, is likely to be wrong; for those of you who are helpful enough to actually do a test yourself.

Thanks.

[The Keeper of Secrets]

Re: Gearbox Springs

If you are talking (and you should be) about the modulus of elasticity (lambda) of the spring then you should use:

Tension in spring = (Lambda x extension in spring)/original spring length.

Apologies if I sound patronising/if you already knew all that.

[MajorLandmark]

Re: Gearbox Springs

Not quite...? Hookes Law

F = -kx
Force = -(spring constant)*extension

This isnt going to be used for actual science per say... Springs tend to be rated in terms of k for engeneering purposes. It's how many newtons of force they provide per meter of spring you use. (or mm more usefully)

[The Keeper of Secrets]

Re: Gearbox Springs

Ah, I've learned it a different way. "Lambda x over L". Having said that, it does still work. My lambda is simply a (N)ewton measurement (modulus of elasticity), whereas the spring constant you refer to is is N/m. Thus you can see where the "/L" comes from. Units work out. The Lambda is a constant and gets rid of the minus sign too. Though I should probably start using -kx. Seems more efficient. The way I do it is just how edexcel are teaching M3 students hooke's law these days.

Anyways, sorry to derail your thread. You might be able to work out the force provided using the energy provided by a 1J spring in the given length of the gearbox. Using the differential of energy (of a mass spring system) as being force (of a mass spring system), with respect to time.

Put mathematically:

d(1/2kx^2)/dt = -kx, or d(ENERGY)/dt = FORCE.

Again, apologies if this is hoplessly wrong/you've tried and it got nasty.

[MajorLandmark]

Re: Gearbox Springs

Now, initially I went to thinking 1J ... shouldnt be too hard. Which is pretty much where you are going with that. Dont forget however, that 1J is the aproximate energy your BB will have leaving the barrel... So taking that back through the volume of the cylinder to give you pressure, and back again to find out the strength of the spring needed to provide that pressure... is just so far that the answer would probably be rather innacurate (since its far from a perfect system) not to mention the fact that its rather long winded.

I can see where your version of hookes law comes from now. I never was that good at making links like that. Yours is probably more useful in terms of mechanics.. which is what M3 is all about.... Mine was an AS physics topic, so we deal in practicality.

Some nice thought into that, which I appreciate, but what im after really, is either a) someone who happens to know what force constant each spring has, or b) someone who has a spare and is willing to test it out for me :D

[The Keeper of Secrets]

Re: Gearbox Springs

Ah, yes do recall the physics now. Phy4, simple harmonic motion? It's almost a second order differential that. Anywho, good point about that. Taking into account friction, air pressure loss and all that, it would be a bit too inaccurate to make the long streams of mechanics worth the hassle.

Anwya, I'll stop annoying you now. If I ever do get some springs I know the rating of, I'll give this a try.

[Caveira]

Re: Gearbox Springs

I'm no engineer, but is it possible to work out how strong a spring is from how much it stretches if you hang a load onto it? If it is, could you work it backwards from a know value for a spring you know the power of?

[The Keeper of Secrets]

Re: Gearbox Springs

Yup, it is possible. Very easy if you measure the natural length of the spring, its extension (stretched length minus original length), and then work out the force it's pulling on the known mass (free body force diagram and newton's laws). Then plug it into whichever formula, and it'll spit out the answer.

[Caveira]

Re: Gearbox Springs

OMG, something must have stuck from O level physics 27 years ago!

[The Keeper of Secrets]

Re: Gearbox Springs

Surely you mean A level. Unless the O level was MUCH harder 27 years ago....which come to think of it it probably was.

[MajorLandmark]

Re: Gearbox Springs

Nice...

So... If anyone would like to measure the length of a spring uncompressed, then hang a known mass off of it, and tell me how much it extends by (or just the new length while under tension) ... and tell me all of those numbers... (lengths masses etc)

that would be cool.

EDIT: And yes, O level was a LOT harder back in those days, as all my A level teachers kept reminding me.

[Phatvortex]

Re: Gearbox Springs

I'm fairly sure compression springs aren't meant to be put under tension. You can deform an AEG spring by pulling it with your hands.

[The Keeper of Secrets]

Re: Gearbox Springs

Good point phatvprtex. Perhaps a better way of doing it would be to use a small mass and simple harmonic motion equations for it swinging back an forth. Be horribly inaccurate though.

[dope_on_a_rope]

Re: Gearbox Springs

Why don't you compress it? It's a stable spring. You could easily just sit a mass on top of it.

[The Keeper of Secrets]

Re: Gearbox Springs

Would that work though? I suppose extension then becomes compression, and works just as well.