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LAN_403

Overclocked

Fri Oct 12 2007, 02:50PM

Registered Member #1056 Joined: Thu Oct 11 2007, 11:15PM
Location: CT, USA
Posts: 27

= BjÃ¸rn BÃ¦verfjord wrote ...
You should also put some effort into measuring the projectile speed accurately so you can judge your progress.

I do have a method and it involved a ballistic pendulum. Ive used the method to measure how fast my bb gun shoots at, and its pretty accurate at measuring speed. Although, if speeds are low enough, a camera could probably be used.

ADD: Ive been playing around with Barrys RLC Sim and Inductor Calc. Ive gotten everything to be pretty optimized and such. Values: V= 250, R= .230 Ohms, C=7000uF, and L = 120uH. Looks like Im not using magnet wire for this one, as its resistance would be to high. Instead I will be using the wire I used to generate high voltage.

Peak current is 764.1 A, with a time of 6mS. 6mS seems a bit slow, but I'll give it a go.

rupidust

Sun Oct 14 2007, 07:00AM

Banned
Registered Member #110 Joined: Fri Feb 10 2006, 12:23AM
Location: Banned City
Posts: 85

Dave:
Stop sending me 4hv tight nit community gestapo notes. Give 1 iota of what you think or say I do not.

Never expect a surplus store to educate you by providing spec sheets, for they are not ordained suppliers. If one does not have the exact data sheet, one can always find a similar data sheet or acquire a similar documented device.

One can also have or attempt to learn about the "type" or "class" of devices being dealt with prior to purchasing, but this special bread of person needs neither mine nor anyone else's answer to help for this person does not ask so frivolously in the first place.

Simon

Sun Oct 14 2007, 08:18AM

Registered Member #32 Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549

rupidust wrote ...

Dave:
Stop sending me 4hv tight nit community gestapo notes. Give 1 iota of what you think or say I do not.

Then how long do expect to last here, exactly?

Dave Marshall

Wed Oct 17 2007, 02:23AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Problem solved, please feel free to continue the conversation.

Dave

Overclocked

Thu Oct 18 2007, 10:21PM

Registered Member #1056 Joined: Thu Oct 11 2007, 11:15PM
Location: CT, USA
Posts: 27

I think Ive gotten this all Figured Out. I thought Coil guns Were Just "Hey Lets build this thing as big as we can!" Nope. I think I finally understand the RLC Circuit.

In a sense, Your Solving for XL and XC, or atleast when L and C are in Phase with each other and are Equal to R. Im guessing when that happens you get a whole crap load of current Induced into the Inductor From The Capacitor, which then causes a electromagnet field to develop.

Also, which is Better, a Solenoid Shaped coil or a Pancake Shape?

Coyote Wilde

Fri Oct 19 2007, 12:07AM

Registered Member #175 Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111

Depends on your capacitor bank. The normal solenoid type is a Reluctance Coilgun, and works much better at lower voltages and longer pulses. The induction coilgun is the one that uses the pancake shape, and it works by inducing eddy currents in your projectile and repelling it. Need a much faster pulse, higher voltage bank, and while the switching becomes more difficult at HV, you don't need to worry about 'suckback' as in a reluctance type (if the field is still on after the projectile has passed the midpoint, your projectile is sucked back towards the centre). You can also use a solenoid coil in an induction gun, but most people just use pancakes. I should note that if you try and stage an induction gun using solenoids, you have the opposite problem of suckback in that you can't trigger until the projectile is halfway through the tube. Or over the tube-- this kind can have an annular projectile riding over the tube, which doesn't work so hot for reluctance.
The classic CG most people build is of the reluctance type because it's easier to build a capacitor bank to spec. Hope that helps, and I really hope I got that all right... it's been a while since I've built a coilgun.

EDIT: ...uh, you were probably thinking of the reluctance type, ferromagnetic projectile and all that, from reading your other posts. In which case I guess none of that was useful. oops.

Barry

Fri Oct 19 2007, 02:52AM

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

Overclocked wrote ...
Which is Better, a Solenoid Shaped coil or a Pancake Shape?

For a single stage PIM (pulsed induction motor) a pancake shape has many advantages. It's very efficient because the disk has so much metal next to the coil. It's easy to find an armature -- any old chunk of metal placed on top of the coil will work. Some metals work better than others (aluminum for example is lightweight with low resistance) so experiment and have fun. It's fun to shoot coins of various denominations or from various countries.

But for those of you determined to build a multi-stage PIM, then a solenoid type configuration is your only choice.

The bottom line for all coilguns: The design is all a matter of delivering as much energy as the projectile can absorb in the time and space it has available. Whatever you build, plan on tuning it for best performance!

Cheers, Barry
The geek shall inherit the earth.

Overclocked

Sun Oct 21 2007, 01:07AM

Registered Member #1056 Joined: Thu Oct 11 2007, 11:15PM
Location: CT, USA
Posts: 27

Do the Caps Necessarily have to be Electrolytic? Are Electrolytics used because of their high current capability?

Dave Marshall

Sun Oct 21 2007, 01:36AM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Electrolytics are primarily used because of their high energy density and affordability. Compared to most other types of capacitors, they've actually got rather low current handling capability.

Dave

ragnar

Mon Oct 22 2007, 07:25AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

Dave's right from the energy density / affordability perspective.

Big low-ESL pulse-grade caps (orange Maxwell bricks the size of vacuum cleaners) are more ideal, but they're rare and expensive..

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