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Neat Gauss (Magnetic) Homemade Pistol

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Neat Gauss (Magnetic) Homemade Pistol

Unread postAuthor: boyntonstu » Tue Mar 29, 2011 3:49 pm

[youtube]http://www.youtube.com/watch?v=e0pAHF1yamg&feature=feedrec_grec_index[/youtube]

Joerg, does the trigger look familiar?

Tech: Imagine a series of electromagnets controlled by breaking a beam of light.

I wonder how fast it could accelerate a 3/8" steel ball in a 36" long rifle.
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Unread postAuthor: Alster370 » Tue Mar 29, 2011 3:56 pm

Interesting, but complex technology to master don't you think? You have to remember that you can only put a certain amount of magnetism on an object, the rest is just converted to heat. The efficiency of Gauss/Coil guns is also very low ( sub 5% most of the time). Id still like to attempt to build one though when I have the funds. Something in the style of this:

[youtube]http://www.youtube.com/watch?v=G1q6VsBoHK8&feature=related[/youtube]
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Unread postAuthor: boyntonstu » Tue Mar 29, 2011 3:59 pm

Alster370 wrote:Interesting, but complex technology to master don't you think? You have to remember that you can only put a certain amount of magnetism on an object, the rest is just converted to heat. The efficiency of Gauss/Coil guns is also very low ( sub 5% most of the time). Id still like to attempt to build one though when I have the funds.


To start, I think that you could copy this pistol for less than $10.
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Unread postAuthor: Brian the brain » Tue Mar 29, 2011 4:03 pm

Cool video..But is it real?
I think it looks like one of those gizmo's from the late 70's.

Where one ballbearing hits another and transfers its energy.
click-clack-click-clack.

One bb seems to be held under the hammer, 4 magnets hold bb's.
apon releasing the bb, it hits the magnet, transfering it's energy to the next bb wich does the same thing.
It's hardly building up speed, if any.
Interesting concept...but..
Not really a gauss gun..
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Jimmy K » Tue Mar 29, 2011 4:10 pm

I built a Gauss rifle a while back- it had 15 neodymium magnets in line with 2 ball bearings after each magnet. It could send the last ball bearing fairly far.. I remember myself being impressed, not much more. I think it was around 2 or 3 feet long.

Here is the basic design I used with an explanation.
http://scitoys.com/scitoys/scitoys/magnets/gauss.html
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Unread postAuthor: DYI » Tue Mar 29, 2011 6:50 pm

You have to remember that you can only put a certain amount of magnetism on an object, the rest is just converted to heat. The efficiency of Gauss/Coil guns is also very low ( sub 5% most of the time).


That would be assuming that you're foolish enough to be trying to pull the projectile, when you should be trying to PUSH it. Induction coilguns are a viable technology, capable of respectable double-digit efficiencies and very high speeds with a well designed multistage construction. Please try to avoid lumping them in with the horribly backward (yet often quite intricate) reluctance technology that the hobbyist community is so inexplicably fond of.

A coin shrinker gives some idea of the repulsive forces achievable in an induction gun - it accelerates a few grams of wire fragments into a kind of radially expanding circular blade, easily exceeding 400m/s with what amounts to a single stage (you'll see claims of about 1400m/s fragment speed on Bert Hickman's site, but I doubt he's ever measured them).

@boytonstu: A gadget like the one you posted was actually some of the main impetus behind my interest in homemade launchers, way back in 2005 or so. It seemed an incredibly ingenious design at the time, and I wondered why it wasn't used more often.

Then I realized that the impressively fast acceleration at the start is very quickly overcome by plastic deformation effects in the construction materials, and, eventually, shattering of the magnets. I believe jimmy101 built an excessively long one a few years back, which you may be able to find on his site. They're capable of a few tens of meters per second with good construction, but you'd be hard pressed to achieve much more.
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Unread postAuthor: more_eggs » Tue Mar 29, 2011 8:00 pm

DYI:
Could you further explain how you would achieve an effective inductance gun? I'm currently studying a subject at uni which is all magnetics and such.. We have to make an AC motor =)
But anyway, I'd like to convert what im learning at uni into a gun... Which was originally going to be reluctance if you remember.. But I'm starting to have a change of heart
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Unread postAuthor: DYI » Tue Mar 29, 2011 8:43 pm

This one's a good example of a small hobbyist build:

Link

Note to moderators: the syntax of the above appears to be correct, but it's not acting like it should...

The projectile is around 3g at a measured 300m/s, with a 1kJ input energy, amounting to about 13% efficiency. That's in the upper reaches as far as hobbyist electric/EM launchers go. Take a look at some of the EML symposium papers for rather more advanced design work. I can't offer much specific advice in the field, as I've never built one myself. In fact, I'd guess from what I've seen that not many hobbyists have, despite the obvious advantages.
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Unread postAuthor: Hotwired » Tue Mar 29, 2011 8:56 pm

DYI wrote:This one's a good example of a small hobbyist build: Link

Note to moderators: the syntax of the above appears to be correct, but it's not acting like it should...


It's the menu system on that webpage, you need to right click to get the link to the page you want then put that in googletranslate and then you'll get a working link.

For example the coil gun: Clicky

You lose the menu on the left but you can always go to the main page again Clicky.
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Unread postAuthor: more_eggs » Tue Mar 29, 2011 10:30 pm

In fact, I'd guess from what I've seen that not many hobbyists have, despite the obvious advantages.


See this is the problem.. Its quite hard to find info on them, hence why noone is building them (because noone has biult them :P )
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Unread postAuthor: Insomniac » Wed Mar 30, 2011 12:22 am

Brian the brain wrote:Cool video..But is it real?
I think it looks like one of those gizmo's from the late 70's.

Where one ballbearing hits another and transfers its energy.
click-clack-click-clack.

One bb seems to be held under the hammer, 4 magnets hold bb's.
apon releasing the bb, it hits the magnet, transfering it's energy to the next bb wich does the same thing.
It's hardly building up speed, if any.
Interesting concept...but..
Not really a gauss gun..


Actually BTB, this device DOES increase in velocity with each collision. The limiting factor on the power is the fact that at a certain point, either losses (heat and sound from collisions) will equal the amount of energy being added at each collision, OR the collisions will become energetic enough to start damaging the magnets or BBs.

The energy comes from the way the BBs are arranged in regards to the magnet. Suppose B is a bb and M is a magnet. With an order like this, you would NOT get any additional velocity from each collision (and it would in fact stop after a couple of collisions as losses leeched energy from the system)

(Diagrams have the projectiles moving from left to right)
------->

B MB MB MB MB

In this example, the BB is accelerated towards the magnet, hits it and transfers most of its energy to the next BB... which has to fight the same pull of the magnet which sped up the first BB. Thus no extra speed per cycle.


However, in the video they are arranged like this:

B MBB MBB MBB MBB

In this case, the first BB is pulled all the way up to the magnet's surface, gaining a fair bit of speed as it does so. Upon collision, the THIRD BB in the sequence recieves this energy. However it's separated from the magnet by the second BB. Thus it doesn't have to fight the pull of the magnet as much, as the magnet is acting much more weakly on it (the third BB) than it was on the first BB. So the third BB is launched to the right at almost the same speed that the first BB hit the magnet with.

The cycle then repeats, but each time it's both the BBs initial velocity, plus the velocity it gains as it is attracted to the next magnet, which is transferred. So each collision becomes more and more energetic until losses begin to limit the speed.

(Of course, the magnets are simply acting like springs in these devices... they act as a way to store energy. No free power here!)
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Unread postAuthor: boyntonstu » Wed Mar 30, 2011 6:06 am

"However, in the video they are arranged like this:

B MBB MBB MBB MBB"

Exactly.

Great analysis.

Bravo!

Could this be a little faster?

B MBB MBBB MBBBB MBBBBB
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Unread postAuthor: Insomniac » Wed Mar 30, 2011 4:17 pm

Possibly, but in that case this would be even better:

B MBBBBB MBBBBB MBBBBB MBBBBB etc...

The problem is that the more BBs you've got between the magnet and the one to be launched, the more losses you incur at each point of collision. I also suspect that the sheer volume of material between them will serve to deaden the impact somewhat.

Regardless of what you do, this style of gun really isn't going to give you enough velocity to even approach what a mini combustion can reach. They're more a fun novelty than a practical method of firing projectiles.

EDIT:

Plus, the exponentially decreasing strength of a magnetic field as you move something away from the magnet means that each additional BB will give you less of an increase than the previous one... So the difference between an MBB and an MBBB layout might be signifcant, but going to a MBBBB layout might not give you much benefit at all.
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Unread postAuthor: DYI » Wed Mar 30, 2011 5:55 pm

Plus, the exponentially decreasing strength of a magnetic field as you move something away from the magnet...


To the best of my knowledge, the field strength will decrease quadratically in this case, not exponentially. Other than that, your point is valid.

You know, I don't think I've ever seen one of these carried far enough that there were no further velocity gains, whether caused by plastic deformations or the magnets shattering. Might be a cheap, interesting experiment requiring only a few hundred very hard ball bearings and a bunch of neodymium magnets on a long track...

Also, very easy to write a simulation for in comparison to gas guns :lol:
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Unread postAuthor: saefroch » Wed Mar 30, 2011 8:29 pm

My physics teacher does this demo at the beginning of the magnetism unit every year, and the magnets have to be replaced about every 5 years because of damage from use.

This is a very interesting device as a demo, certainly, but with little practical use because it is very limited in muzzle velocity and wears itself very quickly.
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