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Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158
I've heard that, while iron is attracted to the center of a powered coil, nonferrous conductors like copper, aluminum, and zinc are repelled through the action of eddy currents. I've also heard these coilguns have efficiency advantages. So what's needed to design one of these? I tried beating a penny (copper and zinc) into a pellet shape and putting it barely inside the coil of my coilgun (500uF, 600V coilgun, 45mH, 11Ohm coil) , but firing the gun didn't repel the penny-pellet.
I've also heard that a coil shorted upon itself will also be repelled. So I made a small coil (like 30 turns) out of wire, shorted the ends together, and it fit snugly inside the coilgun. it was not repelled either. Finally, I got a whole spool of wire and set it around the barrel of the gun (touching the main firing coil), shorted the ends of the spool together, and fired the gun. The spool scooted down the barrel about 5mm. So it worked, but not very well. How do you design one of these "induction coilguns"?
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
you need a coil with less turns so that the inductance is lower, di/dt is higher, and thus the induced eddy currents and repulsive force will be higher. careful you don't blow up your triggering mechanism though with the higher current peak.
Registered Member #4659
Joined: Sun Apr 29 2012, 06:14PM
Location:
Posts: 158
so what really matters is how fast the current rises from 0 to max? that's what di/dt means, right (I haven't learned calculus yet, but that's a derivative, isn't it?
I've also seen an Induction coilgun based on "ringing" of the coil, with what's essentially an AC waveform flowing through the coil.
Oh, and the coil shorted upon itself is better than solid copper/aluminum, right?
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Induction Coilgun
