If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
After a couple years of pontificating about coilguns, it's time I actually made one. Have wanted to try, as a barrel, free aluminum tubing from a discarded TV antenna.
This material is pretty smooth, round, thin-walled, hard, and straight. Comes in a convenient diameter, and is already slotted along its entire length (because made by rolling up a flat strip of metal). The slot (approximately zero width) makes the tube notably elastic in torsion, as the two sides of the slot slip past each other. That can be fixed by gluing a sleeve, patch, or nonconductive winding across the slot, some place where we don't care about eddy currents.
I thought it would be instructional to start by finding a pre-wound coil of high impedance, such as from a mains-powered solenoid valve. With that as a sense coil, we should be able to electrically measure the changes in effective L and R when we insert a slotted metal tube, seamless metal tube, solid metal rod, ferromagnetic rod, wooden dowel, etc. Will probably start at 60 Hz; the fancy LCR meter in my lab doesn't do less than 30 kHz.
Does anyone else have experiences to report with antenna tubing, or coil inductance measurements?
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I'm not sure here, but I think that any changes in inductance will be seen more at higher frequencies.
Also, it would be interesting to try and demonstrate the losses due to eddy currents that we all say is so critical to avoid. I would suggest you set up an RLC circuit with a large capacitance and a large inductance coil and capture the discharge on an 'o-scope. Then you can compare the time it takes for the waveform to go to zero for the different cores. The eddy current should add a damping factor so the longer the circuit rings the more efficient the barrel material would be. If the you can establish a procedure for testing barrel efficiency that the community can follow for themselves, we would all benefit.
It seems that wall thickness is the biggest factor in coilgun efficiency as far as the barrel goes. So I would imagine that your tubing would work great, especially at larger energies where the friction of the projectile sliding in the barrel wouldn't be as large of a factor.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
TV-antenna tubing (naturally slotted Al) for coilgun barrel?
