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Registered Member #2848
Joined: Tue May 04 2010, 05:19AM
Location:
Posts: 44
Hello, I haven't been on here for a long while. I just reconstructed my coil gun after a cataclysmic failure several months ago. (It took me this long to get replacement parts)
Anyhow, I'm wondering two things which I can't seem to remember.
For coil design, do you want high inductance with low resistance? or low inductance with low resistance? My gut tells me the former, but I just wanna double check before I reconstruct my coil.
Also, I was having a hard time getting my projectiles to fly straight - they were flipping end over end. I tried using hollow tail type projectiles and that helped a little bit. Do you know of any good way to get the projectile to spin while being launched for flight stabilization without the use of rifling?
I came across this, but the power required to operate such a mechanism on my device would no long make it portable. Any ideas?
Registered Member #1906
Joined: Sat Jan 03 2009, 05:06PM
Location:
Posts: 39
Low inductance, low resistance is most likely what you'd like.
As for the electromagnetic spin stabilization I don't know much myself, but the Rob Wilsford seem to be planning to have such a system on his latest coilgun. Disappointingly there's not much details about it on his page Speaking of him, is he an active member around here?
Registered Member #2848
Joined: Tue May 04 2010, 05:19AM
Location:
Posts: 44
Thanks for the link! I'll see if I can ask him what he is using to power the spin magnets and what rpm he is thinking will be feasibly achieved. For projectiles of that size, close to 100k rpm is needed - and therefore the magnets need to have HUGE amounts of current coursing through them for up to a few seconds. . . . I made a small prototype and got only about 100 rpm maybe a bit more.
Also, another question. Is it best to have your projectile slightly in the coil before firing, slightly out of it, or already traveling at some speed as in a rail gun?
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Resistance - should be the minimum possible, because even a few milliohms will reduce the peak current.
Inductance - depends on your switching design. A low inductance is good for shorter turn on/off times. However, if you have an SCR-switched coilgun its timing determined by the LC time constant and so you would tune inductance for the best performance.
Starting position - plan to experiment. Coilgun performance is very sensitive to starting position. It's typically best when the front of the projectile is even with the front of the coil.
Initial velocity - generally accepted theory says that energy conversion efficiency improves with entry speed. For this reason, multi-stage coilguns have better efficiency than single-stage coilguns.
Spin stabilization - very important for accuracy in a weaponized coilgun. Is 100k rpm really needed? That sounds very high. It would be cool to apply induction motor techniques to directly spin it in the chamber before firing.
Cheers, Barry There is no substitute for power, except for more power.
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I'm back! And I got two questions!
Speaking of him, is he an active member around here?
