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Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
I got them a while ago for sale on bgmicro.com I believe. They don't seem to have them anymore unfortunately. Ebay doesn't even have any cheap ones.
toward the bottom of the page here you can buy just the pins.
Actually these should be fine too, and even cheaper than mine
here are some longer ones, also cheap
Those are all the best deals I could find. The complete solenoids come with several hundred feet of wire, a perfect size coil bobbin, and an external iron frame.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Gah, I can't find any dimensions for the diameter of the pistons... It's crucial for it to be 16mm or less. I've already got myself a barrel with an ID of 16mm.
Also, my efficiency program is done, and I'm getting some nice results. Using data from my FEMM simulations, it calculates a total efficiency of about 30%. The total efficiency do vary with the energy distribution on the stages! I'm gonna do some more testing and see if I've done any mistakes.
EDIT: There's definitively something wrong! With 30 stages, I get a total efficiency of 650%! I've either invented a perpetuum mobile, or there's something wrong with my code. Debugging time!
Allright, I found the error, and did some testing. Using an energy distribution that follows the natural logarithm e, I found the that the best distribution is the one that follows the function E(x)=43.11 E^(-0.344828 x), where x is the coil number. Using this function, I get a total efficiency of 9,2 %. Sinusoidal functions might work as well, but they're more difficult to set up for repeated testing. Gonna try a few different functions and see what results I get.
Registered Member #5059
Joined: Tue May 29 2012, 06:28AM
Location:
Posts: 4
I noticed myself that some of my projectiles became permanent magnet, you can be sure of that by looking a this, the magnetical hesteresis loop show that if you put a ferromagnetic material on a strong field there will be residual magnetism.
It is proved by exp of many people that regular nails left unmagnetized after a shoot. Howether demagnetization does not happen instantly and must be considered in multistage coilgun operation to make sure each subsequent coil generate the same polarity of magnetic field, otherwise back push will lower the efficiency as well as magnetization losses in a projectile. By my own exp the negative impact of different coil polarity is HUGE and may lower the efficiency up to 50% or so.
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Induced permament magnetic field in projectile and coils
