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Registered Member #1513
Joined: Sat May 31 2008, 12:08PM
Location: Russia Klin
Posts: 48
wrote ... There will be many tests done with the LN2 as I have no experience. The copper breaking,
The copper will not break, I tested it. It's resistance goes down about 5 times (from 25C).
wrote ... I am trying to learn CAD/FEMM
FEMM lies :)
wrote ... Goes to 8500A in 1.58/2 ms.
If I had 8500A, I'd like to built an induction launcher. You may see some my experiments with it here
wrote ... I usually will shoot into a cardboard box with sheet metal backing.
I usually shoot in a box with some clothes - it is guaranteed that projectile would not be lost or damaged
wrote ... I have another question. Dealing with the huge electric fields, how far should I keep laptop away?
You might use steel plate between coilgun and laptop.
wrote ... Also, will the photogates/sensing coils be effected by it?
Sensing coils may not be usable. Photogates may be usable, but you might put them in a steel tubes, or use a laser diode which will light throught trunk for a long distances
Registered Member #2311
Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19
Steve McConner wrote ...
It's 48 hours AND new information to add. Bumping isn't information...
I said I misread it.. I also said I wouldn't do it again. You could give some opinion or ideas instead of telling me that I broke the rule that I just quoted and said I broke it.
Anyway, FEMM isn't any good to me right now as I can't verify if my simulation is right. I like the idea of clothing. I will give it a try. This is a multi-experiment kind of thing. I will be doing many test and the induction launcher is on there. Should I just make a steel sheet metal box around the entire apparatus? It would make it somewhat safer if something blew up. The sensing coils can pick up the initial discharge of energy through the coil. I could have gotten bad data from my last experiment due to this. The photogates I will be giving another shot.
Heres what work I have done so far. I built the capacitor bank and drilled/connected the copper bus bars. Next on the list is to build a mounting device for the hockey puck SCR. I will also be constructing the projectile catcher and be looking into connecting copper wire to copper bus bar. In past experiments, the point of failure usually turned out to be the connections.
What materials should I use to hold the LN2? I was thinking some sort of clear plastic like Plexiglas or acrylic glass but I don't know if they will shatter due to the extreme cold,
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Cloud wrote ...
What materials should I use to hold the LN2? I was thinking some sort of clear plastic like Plexiglas or acrylic glass but I don't know if they will shatter due to the extreme cold,
Are you really sure that you can engineer a significantly more efficient coilgun by using ultra-cold copper? Then it's time to experiment with your LN2 containment methods before investing more time on coils. IMHO the containment is a bigger technical challenge than everything else in your project [edit] unless your barrel does not penetrate the wall of LN2 vessel (i.e. is vertical or tilted, and closed on one end).
I have no experience with glued acrylic structures in cryogenic service. But I'm sure the material has large coefficient of thermal expansion, is very brittle at 77K, and will want insulation. Give up now on the "aquarium" look -- even if your walls were clear they would frost up before your coil was chilled to the core.
I know you can store LN2 in an expanded-polystyrene foam box: A principal challenge is to seal the places where your barrel (if horizontal) penetrates the wall. You could also use thin tinned steel, like that in cookie cans and giant popcorn cans, with rigid foam boards on the outside for insulation. The material is easy to work with, seams can be soldered, and it won't suddenly break and spill liters of LN2 on your table and floor. It's thin enough that I wouldn't expect trouble from magnetic attraction to your coil esp. if coil is inside an iron core. Barrel penetrations might be sealed with epoxy or RTV silicone or even hot-melt glue (?) -- no matter how you do it, it will be hard to separate a horizontal-axis coil from the cold box.
How are you going to deal with frost inside your barrel?
Registered Member #2311
Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19
Klugesmith wrote ...
Are you really sure that you can engineer a significantly more efficient coilgun by using ultra-cold copper? Then it's time to experiment with your LN2 containment methods before investing more time on coils. IMHO the containment is a bigger technical challenge than everything else in your project [edit] unless your barrel does not penetrate the wall of LN2 vessel (i.e. is vertical or tilted, and closed on one end).
I have no experience with glued acrylic structures in cryogenic service. But I'm sure the material has large coefficient of thermal expansion, is very brittle at 77K, and will want insulation. Give up now on the "aquarium" look -- even if your walls were clear they would frost up before your coil was chilled to the core.
I know you can store LN2 in an expanded-polystyrene foam box: A principal challenge is to seal the places where your barrel (if horizontal) penetrates the wall. You could also use thin tinned steel, like that in cookie cans and giant popcorn cans, with rigid foam boards on the outside for insulation. The material is easy to work with, seams can be soldered, and it won't suddenly break and spill liters of LN2 on your table and floor. It's thin enough that I wouldn't expect trouble from magnetic attraction to your coil esp. if coil is inside an iron core. Barrel penetrations might be sealed with epoxy or RTV silicone or even hot-melt glue (?) -- no matter how you do it, it will be hard to separate a horizontal-axis coil from the cold box.
How are you going to deal with frost inside your barrel?
Raised a few good points. I plan to test it all after Monday. I don't care for the aquarium look. If the plastic worked then that would be great. On the cad pictures, I just wanted see through walls so that you could see the coil and overall design. I will be testing both the foam and steel boxes. I didn't think of the cookie tin boxes, nice idea. I think the Styrofoam as a container will leak and not be able to withstand the recoil. Frost on the inside will be dealt with as it comes.. I will try a variety of approaches . I may use a much smaller projectile so that it wouldn't be wedge in by ice. I can also use a heat gun to blow hot air in before I fire. Another idea is using two barrels or a insulated wrap outside of one barrel (kinda like the double pane glass).
Registered Member #2311
Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19
Well, school is killing me. I have 17 credits (13 of which eat my time) plus 4 credit research + workstudy... so.. yeah
I haven't done any of the LN2 testing due to time availablity and limited testing I could do back then. It will be done this friday. I also finally found some hockey puck diodes on ebay. I also just recently found a 800vac transformer for 100ma.This solved my "capacitor blowing up" problem and "charging the capacitor up" problem. The rest shouldn't be a problem. I made the barrel out of some PVC I found. Its wall diameter is a little thick so I may thin it out. I also found some good steel/iron projectiles. Now I need to figure out how to laminate it (or I could buy it..).
This friday, I will be constructing the.. firing platform LN2 box (which I will test tuboware and cookie giving box thingy coil safety circuits (power resisitors from last project incase I need to discharge it really fast) control panel photogates/sensing coil circuits.
The diodes/transformer are in shipping right now so those have to wait.
Registered Member #2311
Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19
I hope this isn't considered bumping. It is new information Control panel mostly built. The voltmeter is not attached to the panel yet. So.. LN2 box.. I found out that many things do work for it. Right now, I am using a cut up plastic coffee can. I did a few materials test to see which would seal the ln2 and also survive the recoil (brittle won't work) from the coilgun. Corona dope proved to be quite good, but it turned out to be brittle. epoxy was a disaster. I am looking at silicon type substances now. Surprisingly, PVC is quite strong under LN2. It may be due to the somewhat bigger wall thickness than I wanted, but it works. Also, electrical tape cracks at LN2 temps. All the materials survived the re-thawing tests. I took apart a spare transformer and separated the E leaves to build a cage around the coil.
Next friday: building a majority of the gun. I don't see any real tests this week though.
Questions: anyone can think of a good sealant for LN2. It will be used to connect the tube and the box togethcer. RIght now its a pressure fit but isn't perfect and will leak slowly.
Registered Member #2311
Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19
Month later: Still working on it
The capacitor bank is assembled and has been charged to 200v (out of the 1050 it is designed for). The coil has been built. It is made up of 12zwg wire with 4 layers and 2-3 inches long. I can get better measurements later. Each layer is wrapped in electrical tape to hold it form. This will reduce its cooling ability bue I don't see this as a big issue as the entire thing will be submerged in LN2. The iron cage housing has been built to fit the coil. Things to do - Mount SCR and protection didoes Get more LN2 Find new container as mine is now to small Start shooting!
Registered Member #2311
Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19
If everything works out, I should be shooting this weekend. I have had problems mounting the diodes and SCR. I think I can get it now using some G10 insulating plastic and C clamps. Sorry I didn't see your post before. It seems like no one is interested until I start posting videos and pictures. Things to do: Mount SCR/Diodes (already have the plan on how to..) Make the big wire connections from coil to copper (already have idea on how to do this) Make new box (again, I just thought of it recently) connect control panel wires up to scr,switches,etc.. rig up photogates/sensing coils if everything else works I truly hope to finish the preliminary shots on Friday/Saturday
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Coilgun help
