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Storing Data on Projectile

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DerAlbi

Wed Sept 16 2015, 06:27PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

By having a read head exactly after the write head. That disables the gun if that part of the gun does not work properly. That gives you one shot after tempering with the gun. You will need that to test the gun after disassembly.

Projectile marks wont happen since the barrel is the way weaker material.

I told people exactly what the goal here is:

The goal would be to imprint some magnetic remanence and to store maybe 20 bits along 40mm projectile

The projectile comes out of the gun pretty much saturated and "whiped".
One could try to punch holes in that remanent magnetisation by havin a ultra short coil that has a reverse magnetic orientiation than the drive coils.
But i can imagine that this is not focussed enough.

Ash Small

Wed Sept 16 2015, 09:11PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

DerAlbi wrote ...

Projectile marks wont happen since the barrel is the way weaker material.

Ceramic barrel?

Dr. Slack

Wed Sept 16 2015, 09:43PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

DerAlbi wrote ...

I told people exactly what the goal here is:

The goal would be to imprint some magnetic remanence and to store maybe 20 bits along 40mm projectile

With respect, that's your proposed solution, not what the fundamental problem you're trying to solve actually is

DerAlbi

Wed Sept 16 2015, 10:09PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Barrel will be some low friction plastic. In a coilgun is not good for efficiency to mechanically alter the projectile. it also does not work when the projectile is shot multiple times (coilgun projectiles are reusable!). There is not much left except magnetic storage.
But i see, no discussion of how one can imprint some magnetic remanence representing data will happen here.
And no, thats not my proposed solution. Its just the way to go in a coilgun and its the thing that needs a solution since i have no idea how to do it properly and if its even possible or what factors determine the "doability" or how i can come to some estimation of how high the data density can be and when this sentence will end...
I just presented my initial thoughts on that, sry if that was confusing.. bad initial description.

2Spoons

Wed Sept 16 2015, 10:27PM

Registered Member #2939 Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615

Have you considered embedding an RFID memory chip? Like this one:

I have no idea how well it would survive launch in a coil gun, but it could be worth a try.

DerAlbi

Wed Sept 16 2015, 10:55PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Yeah what a solution. i think RFID with inductive coupling is great near a high permeability material that short out every higher frequency making it the perfect shield for the RFID-Tag. Also fondling around before every shot, preparing the projectile, is really attractive to everyone who wants to shoot a coilgun. Not to say the additional cost of such stuff.
Of course, lets ignore the obvious way to go like using the natural available media for storing information... like.. uuhhmm.. the projectile itself?
I think, i just should use edding and write a serial number on each projectile. thats good.
Or built in a iron rasp inside the barrel. Wasting some joules of the hardly earned kinetic energy is allways a good solution.
Or what about attachting a string with hotglue. That links the projectile to the gun for sure!
Or i just change the coil drive and shoot backwards, that would imprint a dna-sample of the shooter on every projectile. Usefull too. Way to store information!
Why not throw the coilgun, instead of shooting the projectile? That would circumvent the problem too!

Sry, i currently feel like the next post will propose that i should buy a dog that chews on the projectiles.
Am i really so bad at explaining that i am seeking a discussion on how to imprint magnetic information to a solid iron projectile and what i could expect and how to achieve it?

Ash Small

Wed Sept 16 2015, 11:22PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

My understanding is that data is stored in ferrite, not iron.

Ferrite, in my understanding, comprises numerous seperate 'grains', whereas iron is, in my understanding, some form of crystal lattice compriseing much larger grains, hence the eddy currents, etc.

I'm not sure it's possible to store information in iron in the same way that it's possible to do on magnetic tape, for example.

In my understanding, you need tiny grains in order to magnetise different sections with different polarities.

Even if you could produce such a projectile, others could produce projectiles consisting of a single large crystal of iron, or certainly get close.

That's just my understanding, though

DerAlbi

Thu Sept 17 2015, 07:56AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Thaaaaaank you for resonse on topic

The "grains" you describe are the magnetic domains within those the magnetism is aligned. See:

As you can see in the pictures the orientation can change within the solid iron.
I cant think that in a hard drive you have purposely single grains. Its surely a single surface isolated by crystal boundarys like within the iron.
I think the material that is specially made for magnetic storage has just a much more optimized hysteresis loop. (so that no accidential magnet field easily destroys the data and so that the remanent field strength is higher for better read out)

I never noticed directly that my projectiles were magnetized after a shot. However i noticed that changing the orientation degraded performance. So a shot does have some "impact"

on the projectile.

In the link to wikipedia the paragraph about "Why domains form" stated that it is a "low energy state" when the grain magnetisation does not create a strong external field. That actually would have some impact on how one should write to the projectile: instead of having single oriented large domains, one should try to imprint a frequency modulation. That should than be more stable... right?

Ash Small

Thu Sept 17 2015, 12:11PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

And then there is the difference between 'soft' iron and 'hard' iron.

In my understanding, soft iron, ie annealed, is ideal for, say, transformers, because it has no 'magnetic memory', and is not 'permanently magnetised.

Hard iron, ie work hardended, can be permanently magnetised, ie it has a magnetic memory.

I imagine you'd need 'hard iron' in order to permanently magnetise it, but what's to stop people making soft iron projectiles with no magnetic memory?

That again, is just my understanding of some of the issues here.

EDIT: Imprinting a 'low frequency' signal does sound like the way to go, if you can overcome the other issues

DerAlbi

Thu Sept 17 2015, 02:06PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

"Low frequency"

Lets see: 100m/s and 2mm bit length: so you got 20us time for one bit. Using a frequency fitting at least 4 full waves inside one bit, makes the wavelength 0.5mm so 5us for one period. Thats 200kHz. Aww

Does anyone know what the skin effect does here? i mean: it determines the equivalent thickness for resistivity. but does that mean that magnetic field lines wont penetrate? Will eddy currents inhibit the magnetisation at all?

Hmmh. Do i even need to reprogramm the iron? I mean it comes completeley saturated from the last acceleration coil.... soooo.. all i need to do is to get rid of the magnetisation and thats it allready.

Hard/Soft magnetic: afaik my projectiles are made from steel. that makes them hard magnetic. as i said: the remeber the last magnetisation which showed up in performance problem in my coilgun.

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