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Magnetic Damping of Fully Automatic Launchers

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Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: cammyd32 » Wed Feb 19, 2014 5:45 pm

Recently I have been doing some work on trying to reduce the cycling rate of fully automatic, blowback hammer based launchers.
Many have tried in the past to get a bolt cycling in fully automatic but nearly every attempt results in the buzzing noise of failure, indicating a cycling rate that is far above what could be considered practical.

After considering some more conventional methods such as increasing hammer mass and fine tuning spring tension, I decided to perhaps delve into more unconventional methods, one of which is magnetic damping.

The theory is this, two powerful magnets placed at the rear end of a travelling aluminium bolts travel could cause a damping effect such that the bolt 'sticks' and causes a time delay enough to reduce the cycle rate.
The bolt, slowed down enough such that it does not directly 'bounce' when it reaches the end of its travel, should be prevented from accelerating as sharply due to the damping effect on the bolt when the force from the spring is at a maximum, therefore reducing the speed of the bolt without having to change to a heavier hammer/bolt, or stronger spring.

Eddy current damping.JPG
Eddy current damping.JPG (27.47 KiB) Viewed 755 times


So my question is this, do you think the idea would be at all practical in comparison to alternate means?

I know that 'fine tuning' the design as it were would be a lot more effective, but this could be implemented in places where the design restricts adjustment, or alternately where people are just too plain lazy to do the calculations.

Thanks all for any opinions you would give, I know its quite an abstract idea, but I know the files have seen quite a few far fetched ideas in the past, *Cough* JSR so whatty'all think?
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: jackssmirkingrevenge » Wed Feb 19, 2014 6:22 pm

cammyd32 wrote:Many have tried in the past to get a bolt cycling in fully automatic but nearly every attempt results in the buzzing noise of failure, indicating a cycling rate that is far above what could be considered practical.




The classic angry wasp ;)

The thing with using magnets is that you still have to "tune" it to some extent - if it's too strong, the bolt will stick, if it's too weak it will have no effect.
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: Ragnarok » Thu Feb 20, 2014 11:11 pm

jackssmirkingrevenge wrote:The thing with using magnets is that you still have to "tune" it to some extent - if it's too strong, the bolt will stick, if it's too weak it will have no effect.

There's only an induced current if the magnetic flux is changing, so eddy current braking only opposes motion in a dynamic system. It should only ever slow the system, but never make it properly stick (much like aerodynamic drag slows bullets, but never makes them get stuck in mid-air) - although I guess it's possible the magnets could interfere with whether the spring can move freely.

It's certainly an idea that should slow down the cycling of the bolt, but without knowing how much it needs to slow the bolt by, it's hard to say if it'll be enough.
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: mobile chernobyl » Fri Feb 21, 2014 10:46 am

In the diagram, it looks like the magnet is external to the whole assembly, and the assembly consists of a main tube with the hammer inside of it. What material are you constructing the main tube of? how thick is it?

This magnetic dampening effect works by having the magnet as close as possible to the material without any conductive materials in between - this will greatly diminish if not completely nullify the magnetic dampening effect (unless ferrous). Also the distance apart is very important as magnetic field strength diminishes in a cubic fashion - very quickly the farther away you get!

I'm assuming the classic neodymium magnet dropped in a copper tube inspired this idea? It's a pretty cool example! :)
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: Anatine Duo » Sat Feb 22, 2014 9:58 am

I like the way you are thinking!

you could also put the magnets on the bolt, add a coil... put some of the current to use...
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: cammyd32 » Sun Feb 23, 2014 7:11 am

Thanks for all the feedback folks,

although I guess it's possible the magnets could interfere with whether the spring can move freely

I suppose I never considered that possibility, i don't suppose the effect on the spring itself would be massive though, as by matter of comparison, the spring is quite far away from the magnets.

In the diagram, it looks like the magnet is external to the whole assembly, and the assembly consists of a main tube with the hammer inside of it. What material are you constructing the main tube of? how thick is it?

This magnetic dampening effect works by having the magnet as close as possible to the material without any conductive materials in between - this will greatly diminish if not completely nullify the magnetic dampening effect (unless ferrous). Also the distance apart is very important as magnetic field strength diminishes in a cubic fashion - very quickly the farther away you get!

Well the diagram was more of an illustration of the principal as opposed to a practical application of it, in reality I suppose the magnets might actually form an integral part of the wall, so they are as close the the bolt as possible and have as much effect as possible,

I'm assuming the classic neodymium magnet dropped in a copper tube inspired this idea? It's a pretty cool example! :)

Yup!, got given a load of powerful magnets a few days ago and have been playing with them ever since :P

Well given some more thought I think that its fairly conclusive that the theory would still require quite a bit of fine tuning, and is no way going to be an 'easy fix', I might come back to it later, but only if other more conventional means of reducing cycle rate don't work out for me, maybe using it as an additional means to reduce cycling rate, along with a more finely tuned system.
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: dart guy » Mon Mar 17, 2014 12:32 am

I have a feeling that if you made that with the magenets within a metal peice you would be screwed because it would be slowed either way, you would need PVC to get it to work.
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Re: Magnetic Damping of Fully Automatic Launchers

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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: cammyd32 » Mon Mar 17, 2014 4:41 am

dart guy wrote:I have a feeling that if you made that with the magenets within a metal peice you would be screwed because it would be slowed either way, you would need PVC to get it to work.


Not really.... I have a suspicion that you don't actually know what you are talking about here, magnetic damping is the result of eddy currents formed within a conductive metal, (aluminium bolt) generating a flux that counteracts the motion of the moving metal, given that the magnets are permanently mounted on the rear area of the bolts travel, it would reduce a significant amount of the 'bounce' associated with a speedily oscillating bolt, and overall reducing it's velocity in the rear portion of the bolts travel, reducing cycle rate.
In no event would PVC even effect the whole process so I really don't know why you suggested it? The only place it could possibly make sense to use it was in the walls of the system, but as was previously discussed, in reality the magnets would actually be embedded into the wall of the system, resolving any issues of reduced flux from the magnets outright.
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: dart guy » Mon Mar 17, 2014 2:26 pm

I thought that if you put a magnet in something like a copper pipe it would slow it down the whole time, the PVC would allow only a certain section, like near the back to be slowed
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Re: Magnetic Damping of Fully Automatic Launchers

Unread postAuthor: cammyd32 » Mon Mar 17, 2014 3:05 pm

I think you have misread the diagram I made, the magnets are mounted to the tube in which the bolt lies, permanently fixed in place, therefore only effecting the bolt as it travels past it. Not mounted inside the bolt as I think you are imagining it.
Eddy currents and consequently flux which opposes the motion of the bolt can be imagined to be generated when the bolt travels past the magnets, or when it is 'cutting' the flux lines. Have a read through here, and have a look here, I think the video demonstrates the principal nicely.
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