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LAN_403

PYLEMET-mk2

Sun Nov 01 2009, 10:53AM

Registered Member #1513 Joined: Sat May 31 2008, 12:08PM
Location: Russia Klin
Posts: 48

Cloud, to isolate your LN2 box you can use ~5-10 layers of polyfoam and aluminium foil

wrote ...
It seems like no one is interested until I start posting videos and pictures.

because nobody can figure out your constructions without photos

Barry

Sun Nov 01 2009, 03:35PM

Registered Member #90 Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301

Don't worry, you have lots of lurkers who are watching your project development with interest, even if they (I) don't post comments along the way.

All I can contribute at this time is ... Coilgun performance is sensitive to the total loop resistance in the discharge path. Even a few milliohms will make a significant difference. So I am keenly interested to see a good controlled comparison between cooled and non-cooled coils. It will be a valuable contribution to the hobbyist community.

Keep up the good work, thanks!
Barry
If it weren't for physics and law enforcement, I'd be unstoppable.

Cloud

Mon Nov 02 2009, 02:32AM

Registered Member #2311 Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19

So its built.. unfortunately, I was about 10 mins late to the LN2 stockroom so I had none over the weekend. I have the SCR and diodes in a very crude setup using spare copper busbar, G10 (strong insulating plastic), and C-Clamps holding it together. I have shot some random things using a test coil from the older guns I built at around 300 volts (at 0.0051 F, ~230J, about 8% total energy) and it worked flawlessly without the LN2. I also found got a hold of JB weld and set up a test container to see if it will work (looks promising). On testing LN2 with electrical tape, it cracks it so this may be a problem if my coil gets damaged by the iron cage (that is built now!) from recoil/scratches.

I really do appreciate you two posting. Makes me want to work on it even though I have no choice. More to come on friday.

Edit:
Pictures
Link to zip file

Cloud

Thu Nov 12 2009, 02:15PM

Registered Member #2311 Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19

Another update.
So I got the LN2 but I had to wait for the JB weld testing platform to dry, and then apply it to the new firing rig. Tomorrow, I will be doing LN2 testing.
But for a little appitizer, I have fired the coilgun at 950V of its 1050 v safety rating. I don't have any bleeder resistors nor do I have any balancing resistors. I manually checked the voltages of the 3 different rows of capacitors (which are in series with each other), and they only vary by 10V with the middle row 10v higher then the first/third row.
My projectile right now is a steel slug that gets moving quickly. I am in the processes of constructing the optical sensors rig for velocity measurements.

Cloud

Thu Nov 19 2009, 07:55PM

Registered Member #2311 Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19

LN2 testing delayed once again. I've been swamped with tests and the LN2 managed to boil away over the week. The sensing circuit is built but not tested.
For everyone trying to keep up with this, I am really worried that the coilgun as a whole could be damaged over many the many tests so I want to have data for every shot I take. This is why there are so many delays as I can't afford to rebuild if anything major goes wrong.

Cloud

Tue Dec 01 2009, 12:57AM

Registered Member #2311 Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19

Sensing circuit is working.. first test without LN2 are here..
2191 total joules used at 925V (of 3 caps in series)
309/350V used in each capacitor
35J/2191J=1.6% efficiency

Raw data in case of an error in calculations
Projectile Traveled 25CM in 11ms
Projectile weight is 132grams
Caps are 3 in series, 7 wide in parallel (21 caps)
Cap is 2200uF (.0022F) and 350V
Efficiency will go up as I fine tune the gun and get better projectiles (heavier and less air gap).
I know so many delays but it is getting really close now.

Also, for some reason the induction tests are not working. Is it heavily dependent on the air gap between coil and the projectile?

Edit: So I did a LN2 test and everything went down the drain..
First, the sensing circuit started acting up so I didn't get any reliable data. The first shot managed to crack the container on side and bottom. The 2nd shot I saw a spark on the capacitor bank (and the projectile came out the wrong end). The third/forth shot the LN2 had vanished due to an unseen crack on the bottom.
I have taken apart the coil and container and inspected everything. I redone the electrical tape on the iron cage as it was done for. I am now building a wooden box as it seems like a good idea (built in insulation, easy to work with, hopefully will handle the temperature difference). I have also decided to replace the barrel with a longer one to rule out the EMF field effecting the photogates. I now have new projectiles that reduce the air gap (larger diameter), different lengths, and made of steel

Edit: pictures here

28MB I know.. I can't take pictures!
Will be testing new box soon!

PYLEMET-mk2

Wed Dec 09 2009, 08:15PM

Registered Member #1513 Joined: Sat May 31 2008, 12:08PM
Location: Russia Klin
Posts: 48

Cloud, I have see you photos. You doing much wrong:
1. Coil is too small
2. wires to coil is too thin
3. "Hockey puck" SCRs must be pressed with a round electrodes as you could see on image:
971587

4. I think plastic and tape will be destroyed at LN2 temperatures

and I think that if you have so much caps, you'd better made a railgun than a coilgun. Or you need very big coil and projectile diameter

Cloud

Wed Dec 09 2009, 09:33PM

Registered Member #2311 Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19

Thanks for the feed back.
1. I will make an even bigger one next time, how big do you suggest? I was limited on amount of 12awg wire left over.
2. the wire to the coil are the same wires used in the coil. They are an extension and they get really cold as the copper is thermally conductive.
3. It works for me and I see many people doing it this way. Stores sell the heatsinks that are flat as well.

4. Which plastic? some of the zip ties manage to stay together. The electrical tape was pretty damaged by it but for now is my only option.
My projectile is 3/4 inch diameter weighs 130grams (new one is 200grams). I don't want to make a railgun due to.. things blow up and they cost money.
I look forward to your response.

PYLEMET-mk2

Fri Dec 11 2009, 11:22AM

Registered Member #1513 Joined: Sat May 31 2008, 12:08PM
Location: Russia Klin
Posts: 48

1. I don't know how big - I never make coilguns bigger than 8mm dia. But you can see big dia coilgun here

to compare with yours
3. maybe US hockey pucks are different than russian hockey pucks :)

wrote ...
I don't want to make a railgun due to.. things blow up and they cost money.

the only thing that could blow up in your railgun is barrel - it wouldn't cost a lot of money (except if you make it of gold). And its no need for SCRs. You can see some photos of 8kj handgun railgun in this topic

Cloud

Fri Dec 11 2009, 03:42PM

Registered Member #2311 Joined: Thu Aug 20 2009, 03:07PM
Location: Houston,Tx or Troy, NY
Posts: 19

1. Mine is about varying from 15 to 18mm diameter. I will make a bigger one down the road.
3. They must be, it doesn't have the lip at all.
4. I am interested in coilguns, not railguns. I am seeking a way to accelerate things without damage. Railguns damage themselves.

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