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Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
that is a really small projectile for that much power. I am making a similar one, but with 4 of those caps each stage. Also, ide try putting the caps in parrallel, it might work better with shorter pulse. I am using a 3/8in barrell, for projectiles just over 1/4in (silicon steel rod i found in sprinkler vavles).
For the coils, i was going to use 2 layers of 12 AWG wire, i think 1.5-2in long, this would give a pulse of almost 8KA. Have you got SCR's yet?
Use barry's RLC sim and inductor sim to plan a coil:
Registered Member #968
Joined: Fri Aug 24 2007, 04:54PM
Location: Norman, Oklahoma
Posts: 104
I'm definitely going with a multistage coilgun this time. I am choosing a smaller boresize to maximize acceleration, as I plan to have very accurate velocity and acceleration readings after each of the 4 coils. This will allow me to modify coil timing and spacing to maximize efficiency.
I will also be doing control in the CG and may modify the last stage to achieve a desired exit velocity below the maximum achievable velocity for more repeatable ballistic effects.
For projectile I will most likely use cold rolled steel for now, it has worked well for me on previous CG's.
Has anyone tried butyrate tube(CAB) for a barrel? It looks like it can be found with wall thickness as low as 1/32".
I have some newer SCRs on the way but am not sure they will do the job. Also have a moderate IGBT on the way that will.
Going to go try the inductor sim now. Barry has been very helpful to me on my previous "Coil Gun 2" =)
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
smaller projectile doesn't exactly incese acceleration. With too much power, the projectile will saturate, meaning it can't absorb more nergy, wasting all that power, it will just come back as ringback.
You also dont want too thin wall tubes, he compersive forces of the coil might be too much.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Smaller barrels will tend to increase velocity but yield lower kinetic energy because the efficiency is not as good.
The projectile will saturate when its magnetic field reaches 1 - 2 tesla, so a bigger diameter means much bigger cross-sectional area, which means it can carry much higher total flux.
14AWG sounds a little thin for the higher power levels you've got. I'd suggest also trying a 12AWG coil and see what happens.
Series vs parallel caps? As long as the pulse timing is right and the circuit's ESR is low enough, then it doesn't really matter. The total stored energy is the same regardless of how they're wired. It's a practical issue where some configurations can use cheaper switches than others, or be marginally safer to work around. In my totally wild-assed guess, the first stage or two might benefit from parallel caps where the lower ESR will improve peak current levels and the timing is still relatively slow. But in later stages you'll need a mighty short discharge pulse and parallel caps are likely to be too slow; look at series caps and higher charge voltage for those stages.
Hope this helps. Sounds like a great project! Barry You only have to know three things to be an electrical engineer:
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Building "Coil Gun 3"
