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Simple disposable camera coilgun

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LAN_403

Electroholic

Sun Jun 25 2006, 07:32AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

is it 26 or 24 awg?
too thin for 10 PF caps

it doesn't matter where you put the scr in the loop,
floating or not, performance would be the same.

try clean up the charger board a bit, i assume you still have the trigger cap and transformer on it? they might be the cause

Alfons

Sun Jun 25 2006, 08:46AM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

Electroholic wrote ...

is it 26 or 24 awg?
too thin for 10 PF caps

It's 0,5mm, so that's about 24 awg.

wrote ...

try clean up the charger board a bit, i assume you still have the trigger cap and transformer on it? they might be the cause

I have already removed the small caps which were soldered to the boards, so that couldn't be the problem.

Alfons

Sun Jun 25 2006, 03:42PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

Ok; I just wound a new coil, still using 0,5mm wire (I don't have any other wire left and I don't have money at the moment so I can't buy thicker wire).

The coil draws 5,66A from a 18VAC source; so the impedance is Z=(18/5,66)=3,18 ohm, right? So if my calculations are correct, the inductance should be L=Z/(2*pi*f)=3,18ohm/(2*pi*50Hz)=10,1mH...

As I expected, there isn't much difference in performance.

So, what wire diameter would you guys use; and what inductance should my coil have if optimally tuned? (Or how do I calculate that?)

EDIT:
The SCR-issue still isn't sorted out. The problem is the following: I connect the SCR (see circuit some posts above), connect a 9V-source, switch opened. Then I load the caps, when they're loaded I push the SCR switch, but nothing happens. When I disconnect the 9V-source though (switch NOT closed!), the coilgun shoots! I don't understand how this can occur, and I'd like it if someone'd explain that to me.

rupidust

Sun Jun 25 2006, 05:34PM

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

Do you truely want the CG to first work at all and secondly work with performance >= 2%?

* Practice using the SCR at a 12v level using LEDs, lamps, or small motors as a load.
* Practice using the SCR as a LOW side switch, SCR cathode at ground level and load at +12v level.
* The SCR should be known and exprienced prior to high energy usage.
* Use 22 or 20 awg mag wire. Use 6 to 10 layers, make the coil length equal to projectile length.
* Bound the coil with more than helping hands. Any coil movement subtracts from projectile forward velocity.
* Make a graph or table of Velocity/Efficiency Vs. Projectile start position using a fixed voltage, coil, and projectile. The crest of this bell curve graph will be your tuned position. If you are not satisfied, change either projectile, voltage, or coil and remake a new graph or table.
* L inductance = Z/(2*pi*F) and Z = (2*pi*F*L). Better to use a Inductance calculator or a meter because this is not a 50HZ AC application.

Alfons

Sun Jun 25 2006, 05:46PM

Registered Member #134 Joined: Fri Feb 10 2006, 10:44PM
Location: Belgium
Posts: 86

rupidust wrote ...

Do you truely want the CG to first work at all

Yes; it does even work, only not like I want it to.

rupidust wrote ...

and secondly work with performance >= 2%?

Not necessarily. I'd be pleased with 1% too, but of course 2+% would be great

rupidust wrote ...

* Practice using the SCR at a 12v level using LEDs, lamps, or small motors as a load.
* Practice using the SCR as a LOW side switch, SCR cathode at ground level and load at +12v level.
* The SCR should be known and exprienced prior to high energy usage.

That's a good idea indeed. I don't have any experience with SCR's, but I thought maybe it'd work right away (which it didn't), in which case I'd already be pleased

(I know, I know, wrong mentality)

EDIT: I practiced using the SCR at low levels, and I do get it to work. If I connect it to my CG circuit, it still doesn't work, though...

rupidust wrote ...

* Use 22 or 20 awg mag wire. Use 6 to 10 layers, make the coil length equal to projectile length.
* Bound the coil with more than helping hands. Any coil movement subtracts from projectile forward velocity.
* Make a graph or table of Velocity/Efficiency Vs. Projectile start position using a fixed voltage, coil, and projectile. The crest of this bell curve graph will be your tuned position. If you are not satisfied, change either projectile, voltage, or coil and remake a new graph or table.

Ok; I'll try that out and see what results I get.

rupidust wrote ...

* L inductance = 1/(2*pi*F*Z) and Z = 1/(2*pi*F*L) all coefficients in the diviser. Better to use a Inductance calculator or a meter because this is not a 50HZ AC application.

Indeed I know I should do that, but I haven't got access to an LCR meter and I don't have a signal generator or something, so I guess it'll be quite hard to determine the inductance using another method...

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