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Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Hi guys!
Thoght I'd post some pictures from my coilgun project. It's a 9-stage, 3.8kJ one, and the first coilgun I have ever built. I am using two photogates per stage in order to get full control of when each coil will fire. An IGBT module acts as the main switch, while 9 SCR modules control what coil the current flows to. There's of course more to it, but I know you just want to look at the pretty pictures!
Took this picture today, got started on the plate that the coilgun will be mounted on. The copper bars on each side is for current distribution.
Two coils that'll become the first stage
In the middle of winding one of the coils:
Testing a monostable 555-timer. Going to use it to measure the velocity of the projectile.
Here's the 555-timer circuit on a breadboard.
The IGBT controller:
Photogate electronics. I'll need one of these for each stage.
If you have any questions, don't hesitate asking! I'll probably update this thread at least a few times a week with new pictures :)
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
Hey, From what I understand, you have a central capacitor bank, and IGBT switch, and 9 SCR's to direct current to the correct coil. Why not split up the bank and use the SCR's directly? If you want control of the pulse and turn it off when the second photogate is triggered, take a look at the V switch method:
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
Is it just me or are there big gaps between your coil layers? You shouldn't need any extra insulation unless your charging your caps in series
I just got an almost identical sized capacitor bank in the mail today O_o 12x 3900uf 400v = 3.744kJ (+ 4x 2200uF 450v, but they seem light and need tested)
edit: Oh and a fun conversion i made up: Joules to stories dropped by 16lb bowling ball: divide by 235
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
There is a layer of masking tape between each layer of wire. This so that the coil won't unravel when I Remove it from the winding rig, not for insulation. The tape is pretty thin, so it does not have a big negative effect on the coil. Great to hear about your cap bank!
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Pinkamena wrote ...
I was initially going to split the cap bank up in smaller units, but more experienced coilgun builders said that it was a bad idea.
I don't think there's any logic to this. You don't get any advantage by doing it this way, and it makes calculations much more difficult. Notice that the people who claim to be experts and recommend doing it this way have never actually built one... that being said, I'm very interested to see how it works out in your case. Please give us lots of updates!
Question: If you're using SCRs to trigger the individual coils, how do you plan to turn them off at the right time? Is that what the IGBT is for?
Nice work! It's good to see someone else is putting serious work into a coilgun!
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
hmm. To me it looks like your hand is visible through the layers.. Oh well.
Anyways, have you tried using liquid super glue to bind the layers together? I've had great success using it with 16awg wire. Allows the windings to be as dense as possible too.
I can't picture how you're going to get one IGBT to switch all the coils individually with separate banks. Have a sketch of the circuit or care to explain it?
I can only think of three ways of doing it (excluding v-switch stuff): 1. separate banks with an SCR or IGBT per coil 2. one bank with an IGBT per coil 3. one bank with an IGBT to control on/off and an SCR per coil
Oh and where are you getting your SCRs from? I need to find some cheap ones as well.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
Saz43 wrote ...
Pinkamena wrote ...
I was initially going to split the cap bank up in smaller units, but more experienced coilgun builders said that it was a bad idea.
I don't think there's any logic to this. You don't get any advantage by doing it this way, and it makes calculations much more difficult. Notice that the people who claim to be experts and recommend doing it this way have never actually built one... that being said, I'm very interested to see how it works out in your case. Please give us lots of updates!
Question: If you're using SCRs to trigger the individual coils, how do you plan to turn them off at the right time? Is that what the IGBT is for?
Nice work! It's good to see someone else is putting serious work into a coilgun!
Honestly, keeping the cap bank in one piece saved me a lot of time writing my simulation. A single bank for each stage would require me to design the coil so it would use all the energy in the bank on the time it took the projectile to pass through. Not only would the force be varying and relatively difficult to simulate, but the turns/layers configuration for this would likely not be the most effective either. Keeping the cap bank in one piece will allow me to vary the amount of energy per stage, not being bound to a set amount. It literally takes the stored energy out of the equation when finding the most effective coil configuration since I have no lower nor upper limit (within reason of course) for the energy consumption per coil, only for the 9 coils together. The force per stage will also be nearly constant, so calculating the work per stage is much simpler.
Regarding the SCR question, you are correct. The IGBT and one of the SCRs will be turned on at a time. So the IGBT will turn on and off 9 times per shot, while each SCR will only turn on and off once. And thanks for the kind words! Your own coilgun projects have really inspired me.
Forty wrote ...
Anyways, have you tried using liquid super glue to bind the layers together? I've had great success using it with 16awg wire. Allows the windings to be as dense as possible too.
I can't picture how you're going to get one IGBT to switch all the coils individually with separate banks. Have a sketch of the circuit or care to explain it? Oh and where are you getting your SCRs from? I need to find some cheap ones as well.
Yes, I did try using super glue first, but the two kinds I had available didn't work... So I used the next best thing, tape! And about the switching method, see my reply to Saz :) I do not have any schematics for the switching system unfortunately. And I bought my SCRs from ebay I think. They can't take very high current though, so I gotta put some in series for the last 4 coils which will get a current way up in the >5kA area.
Registered Member #4237
Joined: Tue Nov 29 2011, 02:49PM
Location:
Posts: 117
More pictures! I finally finished the first stage and got it mounted. The control panel is also coming along nicely.
About the iron sleeve: It's made from polyester and iron powder. I used a ratio of about 4 parts polyester, 6 parts iron powder. I wish I could have used less polyester. I first tried a ratio of 1/4, but that just made the iron powder sort of a damp paste that could be molded but not poured into the forms. I used soft rubber sheets to make the forms, and covered everything with vaseline so it wouldn't stick. Worked like a charm.
Stuffed the two pre-wound coils into the sleeve. It's bloody heavy!
Also, projectile and control panel (not finished)
There's two compartments. The lower is for the photogate electronics, while the upper is for everything else.
Here's the projectile. It weighs 75 grams, and is made from a 1/2" steel rod of grade EN1A.
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3.8 kJ coilgun
