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New Big Multistage Coilgun in Progress

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LAN_403

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Fri Nov 10 2006, 10:41PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

okay here we go. a week ago i started my big multistage Coilgun project. i dont want to break any efficiency records here but my goal is to get a very high velocity of around 130m/s- 150m/s. the finished accelerator will have 10 or more stages,.

here is one of around 40 testcoils iÂ´ll make for this big project

Finalcgcoilklein

for every coil the most important data is printed on a small piece of paper, inductance, dc resistance, wire gauge, turns, layers etc. the barrel is a 11,5mm polypropylene tube with an inner diameter of 9mm (for 8mm steel rods 4cm in lenght) every coil will have the same sizes but many different layers, turns wire gauges etc.
i thought of 200joules per stage so 2kj for 10 stages. my hope is to get an overall efficiency of around 4-5% to accelerate a 11 gram steel rod to 130m/s.. i calculated some things out and began with a new high velocity optical triggering system. i simulated everything in SWCad and it seems that even with a projectile that is flying with 400m/s through the fotogate, i can produce a single pulse to turn the SCR on. i added a delay feature on the fotogate to delay the pulse from the fototransistor for a adjustable time of 0-around 2mS. that will solve some problems with high velocity coilguns. every coil has a point where the projectile should be when the coil switches on. but you cant mount a fotogate at this place so you place the fotogate as near as possible to this point. when the projectile switches the fotogate the scr turns on but the projectile is on the wrong place . but with this circuit you can adjust the time and "wait" for the projectile to reach the right place to turn the SCR on.
first tests with the new coils showed an efficiency of around 3-4% with a 2000yf 250volt capacitor, and thats very good for a SCR switch.

here is the shematic and simulation of the new fotogate circuit.

the simulation shows the fastest scenario. the blue line is the gate voltage of the fototransistor,. the ir beam is blocked for about 150Âµs which stands for a projectile speed of 400m/s when the projectile is 5cm long. the green line is the output voltage without delaying. by afjusting R3 from 500ohms to 10k ohms you can delay the output voltage to a max of 2mS , the pulselenght is adjustable with R7..
okay its not digital, but i wanted the whole electronic directly on the fotogate pcb that fits on the coil..

here is another scenario with a delay of around 1,3ms. the fotogate is blocked for 2,5ms which stands for 20m/s when the projectile is 5cm long

More to come soon, finished some coils and calculated some things and everything looks promising, buyed 500 SCRs with 600V 120A iPk

and many IR Diodes and fototransistors.

TheMerovingian

Sat Nov 11 2006, 11:00PM

Registered Member #14 Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383

Looks like a clean design
remember to play with pulsetimes decreasing inductance/resistance or capacitance of stages

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Tue Nov 14 2006, 05:55AM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

My SCRs arrived yesterday and i made a few tests with them, they are exactly what i need. i changed the photogate shematic a bit, now i can adjust the delaytime between 0-700ÂµS and adjust the on time pulse too. the new photogate works with 5 volts and is very sensitive, exactly what i need, that was a lot of calculating and simulating until i got right.

for those who are interested.

and here are only 100 of 500 Scrs i got yesterday,

...

Tue Nov 14 2006, 06:03AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Wow, that is a lot of SCR's

Why didn't you invest in a brick or two?

In any case, is it just me or does it seem like you are kind of overdesigning this... You are only using 200J per stage, but you are using really thick wire and tons of SCR's... I am thinking of hooking a 200J (for lasers) bank up to a little coil I made arround a 1/4" former with like #20 wire...

w00t 777th post, exactly the number of posts I made on the 'old' 4hv

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Tue Nov 14 2006, 05:30PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

no, this multistage CG is designed to experiment with, to add or change components quickly so its well to overdesign it a bit. i got the scrs very cheap on ebay , i payed only around 80$ for 500Scrs . i sell 300 of them in my Forum to limit the costs for me cause i dont need 500 of them. and i dont know how much energy i finally put into each stage,. it can be 200 joules or it can be 800 joules, just what i want to put into it. each component is designed for quick changing, each coil, each capacitor and each other part. everything is mounted on a large aluminium U Profile with holes at the bottom to screw on the coils and fotogates, sensoring etc. and if i loose the interest on a big multistage i can easily use two or three coils to build a portable pistol or something. i can use the whole equipment for every CG related experiment.

you must not see this as one big project, its more like every single coil, every sensor and every cap bank is a whole project on its own

and why do you think i use very thick wire, as seen on the picture its only 1,1mm wire and its only 1 coil of many coils iÂ´ll build for this project, and as described above, with different layers, turns, wire gauge etc

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Sat Nov 18 2006, 04:40PM

Registered Member #76 Joined: Thu Feb 09 2006, 10:04AM
Location: Hemer, Germany
Posts: 458

finished a few more Coils today and made some more coil supports with holes for the phototransistors and diodes. build the first 2 fotogates and assembled one of them on a coil. looks like this

works very good and is very accurat. i drilled a 3mm hole through the barrel and the coilformer and drilled it on both sides to 5mm to fit the diodes in it. so i have a fotogate which switches within this 3mm. the pot is to adjust the delay between switching point and pulse point (when the output goes high)

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