dietz@SLB-DOLL.CSNET (Paul Dietz) (01/17/86)
>Sorry, computer grade capacitors aren't of any use for >building railguns. They have too much internal inductance >to supply the sort of short, high-current pulse that you >would need. They won't even explode wires! You might >have better luck with photo-flash capacitors charged to >an appropriately high voltage... Rats!
ems@amdahl.UUCP (ems) (01/20/86)
In article <8601171419.AA20243@s1-b.arpa>, dietz@SLB-DOLL.CSNET (Paul Dietz) writes: > >Sorry, computer grade capacitors aren't of any use for > >building railguns. They have too much internal inductance > >to supply the sort of short, high-current pulse that you > >would need. They won't even explode wires! You might > >have better luck with photo-flash capacitors charged to > >an appropriately high voltage... > > Rats! Are you sure about this? Just how short a pulse is needed, anyway? I used 'computer grade' capacitors of about 20,000 mfd charged to 20v or so to launch model rockets (circa 1972). They did a dandy job of vaporizing the nichrom wire igniters! (Though they did have enough charge left after the first launch to ignite one, and sometimes two, additional rockets). It was my understanding that rail guns took a fractional second to a few seconds to accelerate something depending on design. Surely a model could be built that would be able to use computer grade caps? -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems This is the obligatory disclaimer of everything.
henry@utzoo.UUCP (Henry Spencer) (01/22/86)
> It was my understanding that rail guns took a fractional second > to a few seconds to accelerate something depending on design. > Surely a model could be built that would be able to use computer > grade caps? But the output velocity probably wouldn't be too hot, not from a gun of practical length. Assuming a constant acceleration, v^2 = 2ad, which translates as "to get a high velocity, you need either a high acceleration (short transit time, high currents, low-inductance caps) or a very long gun (gets physically cumbersome very quickly)". The problems of gun length are why rail-gun and mass-driver work tends to push for very high accelerations. Phrased another way, again for a constant acceleration, v = 2d/t, which means that a velocity of hundreds of meters per second (a high-velocity rifle is maybe a thousand) means acceleration times of a few milliseconds if the gun is to fit in an average-sized room. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry
ems@amdahl.UUCP (ems) (01/28/86)
In article <6308@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes: > > It was my understanding that rail guns took a fractional second > > to a few seconds to accelerate something depending on design. > > Surely a model could be built that would be able to use computer ***** > > grade caps? > > But the output velocity probably wouldn't be too hot, not from a gun The original discussion was about building a model gun. I took this to mean a lab gun for 'playing with'. Not one that would reach hazardous velocities. I can see where others might take 'model' to mean 'prototype of small size' with realistic performace velocities. > of practical length. Assuming a constant acceleration, v^2 = 2ad, > which translates as "to get a high velocity, you need either a high > acceleration (short transit time, high currents, low-inductance caps) > or a very long gun (gets physically cumbersome very quickly)". The > problems of gun length are why rail-gun and mass-driver work tends to > push for very high accelerations. Phrased another way, again for a > constant acceleration, v = 2d/t, which means that a velocity of hundreds > of meters per second (a high-velocity rifle is maybe a thousand) means > acceleration times of a few milliseconds if the gun is to fit in an > average-sized room. For more modest accelerations, could not the time be extended to a few hundredths of seconds for a 10 metre or so rail gun? (Yes, I know I should do the math, but it is so much easyier to let someone else do it ...) -- E. Michael Smith ...!{hplabs,ihnp4,amd,nsc}!amdahl!ems This is the obligatory disclaimer of everything.