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Gauss Air Gun

auto-charging.
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Gauss guns are cool, but they're only 1-2% efficient: the ammo is too small for the magnets to grab efficiently, and the speed required means energy wasted on magnetic lag effects.

A type of pellet airgun called a "springer" compresses air into one side of a tube, which rushes out the small valve on the other side, propelling the pellet. The action is powered by a spring (coil or gas-strut), manually compressed, released to fire, thus the name. The (relatively) slow motion of the piston is translated into a fast motion of the pellet.

So the idea is to drop in a linear motor, replacing the spring, to drive the compression piston. The mass of the piston rod gives the magnetic field something to grab onto and the comparatively low speed of the piston means a lower acceleration is necessary.

This should allow the efficiency of the action to approach the 80-90% found on most electric motors.

A more refined version has both a half-strength spring and a half-strength linear motor, lined up as spring > motor > piston/cylinder ( > pellet > barrel): the motor charges the spring then changes polarity and assists in the power stroke.

FlyingToaster, Sep 06 2012

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       On a level of Physics, this is do-able, and is of itself not a bad idea.   

       The use of the drive coil in reverse to precompress a spring, then combine stored spring energy with magnetic impulse to drive the piston is good. The magnet can even be used to decelerate and buffer the piston as it nears the end of its travel.   

       However …   

       The coil will be quite big and heavy. The piston will be heavier than on a standard weapon as it needs to have (presumably) a permanent magnet. But most of all, exactly how heavy is the backpack containing the batteries, the capacitors, the drive elctronics and the cooling fans?   

       A 5.5mm airgun pellet weighs about a gram. Typical muzzle velocity is about 150m/s. Kinetic energy is therefore about 11 J.   

       Accepting a cycle rate of 5 seconds, and an overall efficiency of 20%, 55 J in 5 seconds is near enough 11w; from a 12v power supply, that's about an amp, which would be OK for Lion batteries.   

       A nominal 12V 1000mAh battery stores about 40kJ - enough for quite a few shots - if, but only if, you can get that elusive conversion efficiency.   

       It would be interesting to compare with a pneumatic system using a small reciprocating compressor to charge a reservoir.
8th of 7, Sep 06 2012
  

       A laptop battery and a couple small capacitors should suffice: no need for a backpack. The more capacitors added, the faster the cyclic rate could be.   

       I question whether the reciprocating element would be substantially heavier than before: on the basic model there's no spring and on the more refined one both motor and spring are half-sized. Bear in mind there are springers which have mechanisms that cancel the recoil: the same could be applied.   

       figuring 40Wh from the laptop battery, at your specs (or mine: 4.5mm(.4g) and 200m/s) and 20% battery-to-muzzle efficiency, that's a few thousand shots before the battery needs to be changed/recharged.   

       On the other hand, a small radial pump, embedded openly in the stock, would be quite visually appealing. I think that would work best in a reservoir system: the pump could then work at its leisure fuzzily keeping the pressure up in the tank, mostly unencumbered by the user's firing cycle.
FlyingToaster, Sep 06 2012
  

       Indeed. One further caveat, though. It's got to be silent. If you're using the weapon for hunting, then a whirring motor is going to be somehwhat unhelpful.
8th of 7, Sep 06 2012
  

       well... design possibilities are endless, but several come to mind:   

       an early-electropunk model
- toggle-switches,
- brass VU charge meter,
- high-pitched whining capacitor-charging noise,
- exaggerated gauss coil covers
- full forestocked,
- volley sights
  

       future-punk
- blinkenlights, lots of blinkenlights
- Majel Barrett or the B-52 lady commenting on battery state,
- chrome, glass and black polymer
- red dot sights
  

       not that I've thought about it much of course ;)   

       Oh, yes, both would have "FX off" switches.   

       The pump model would probably work best in the steampunk range: similar to the electropunk, but with a couple of pressure gauges as well.   

       <wanders off wondering how many shots you could get out of an early galvanic cell>
FlyingToaster, Sep 06 2012
  

       Tech-Force, a Chinese company (I know, but give it a chance) makes highly accurate, relatively quiet, and reasonably affordable springers that achieve blistering muzzle velocities. They have well-designed ergonomic walnut stocks, and most of their models utilize a front lever-action mechanism that gives the gun a classic carbine or 'over-under' look and a steampunk feel. Start your journey there.
Alterother, Sep 11 2012
  

       //makes highly accurate, relatively quiet, and reasonably affordable springers that achieve blistering muzzle velocities.//
They shoot spaniels?
That's horrible.
AbsintheWithoutLeave, Sep 11 2012
  

       I was looking at those the other day on the 'net. Very muskety.
FlyingToaster, Sep 11 2012
  

       Yes. That is all very well but how does it compare to an anti tank gun for blasting the living shit out of them?
Lesser Spotted Kiwi, Sep 11 2012
  

       A pneumatic system couldn't be a drop-in replacement on a bazooka, but something might be made to work on a mortar.
FlyingToaster, Sep 11 2012
  

       Indeed it can. The airburst pyro fired at EPCOT is all cold-launched from permanent fixed tubes using compressed air. It gives very precise launch sequence timings.
8th of 7, Sep 12 2012
  
      
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