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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Well, ideally, you want to draw it out of the varnish vertically, so you don't get any 'blobs' on the underside, (and you get an even coat), then dry it, then wind it onto a spool, or whatever.
If you just dunk the spool, then let it dry, it will just set into a useless lump of wire and varnish.
You may be able to do a length at a time by submerging, say, 20-30" in varnish outside under an upstairs window, then using a piece of string suspended from the window, pull it up and let it dry (you may be able to do a whole spool by this method, a length at a time)
It needs to be near vertical while it dries to get an even coat.
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600
One thing people haven't explicitly mentioned:
at best, magnetic pressure goes as the SQUARE of the field strength
but so do the I^2 R losses (since field is proportional to current)
And you get the same resistivity losses with lots of thin wires or lots of thick wires, if the fill ratio is the same.
So you want the minimum R for your coil, maximum conductor, minimum resistivity, but then eventually you run out of space (i.e. theoretically 100% fill ratio). Adding extra coil further and further away from the projectile helps less and less.
And the big gotcha for coil guns is that the magnetic pressure doesn't usually go as a square on field strength, but only linearly, at least once the projectile saturates; so in that case you're going to be better off running a lower, more optimal, current (but still filling the space with copper as much as possible to reduce R), at least if you want efficiency, or you can run high current, and then let the coil cool off afterwards and accept the low efficiency.
edit: actually the force goes as the product of the two magnetic fields, if the projectile is soft in the regime you're working, then it's a square law, if the projectile is hard then it's just the product.
Registered Member #2901
Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837
With one big coil most of the coil at any given time is just burning power for the most part ... it doesn't matter if turns are far away from the slug radially or laterally, the farther they are away the less useful they are.
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More wire improves efficiency of a coil?
