Wednesday, November 17, 2010

further increments

Progress on my projects is beginning to look a bit like Zeno's Paradox Of Achilles & The Tortoise, in part because my hands and arms and shoulders hurt too much to do any work.

One thing I can do apparently, is continue to build parts for other projects virtually, in SolidWorks.  Some of my projects could not be built at all -- at least not by me -- without good drawings, accurate dimensions, close tolerances, and a sophisticated 3D model which warns me where I'm about to screw up before I take any cutters to any materials.

I'm having a bit of trouble with the rail connections at the breach of railgun #2. Various amateurs have tried various things, but it seems an awful lot of amateur railgunners forget that it is inductance in the gun that does all of the work, and all the other stray inductance in your connections serves only to slow and limit the current.  In other words, you want low-inductance, low-force connections, cables, and buswork between your power supply and the gun, and you want high-inductance and high force inside the gun ONLY.

I see other railgunners with gorgeously built guns and connections made to a great big expensive capacitor bank twenty feet away through great big SO cables lying on the ground... and I laugh.  So much money wasted.

The big guys use RG-220 or YK-198 high current, high voltage coaxial cables - many-many of them, to connect power supply to gun breach.  I'm searching for a windfall of same on eBay, but I don't expect to find it. That stuff is expensive and not much of it is made. Its tiny market probably holds on to every piece that is still serviceable until it isn't.  So I'll be using bars of copper bolted together, in all likelihood, and that means locating the gun close to the power supply but come on - this is only an 18kJ device for now.

It doesn't help that, like most small-scale, amateur designs, I am using a gas gun pre-accelerator to overcome the standing start problem.  Sophisticated tailoring of power supply to armature shape and armature-rail pre-load can overcome the issue, but that's for the professionals. I don't think that's within the reach of most amateurs, and certainly not I.  But that injector connects to the breach at the back, meaning the rail connections have to come out somewhere else, and away from any nearby bits of metal.

Hopefully, my virtual Tinker Toys will let me find something that works within my means.


In the mean time, what I hope are the final parts for the Mad Scientists Light Switch are en route.

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