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Hey everyone, i'm working on a 2 stage coilgun, and i was wondering how i would go about triggering both stages with a time. I would like to use something like the 556 dual timer to control both stages. Both stages are SCR triggered, so i how would i go about doing this? Thanks in advance!!
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
You're not going to get reliable results using timing. The time it takes for the projectile to reach the second stage is going to changes by large amounts from shot to shot, even if you do place it in EXACTLY the same starting point each time. Coil guns have too much going on to be able to use hard timing.
You need to use a method that is dependent on position, not time. Such as an optical trigger.
Registered Member #2064
Joined: Sat Apr 04 2009, 09:26PM
Location: NJ, USA
Posts: 16
A long time ago I used wire brushes to trigger my second stage. It was pretty crude, because the projectile passing between two brushes directly closed the circuit between the coil and the capacitors generating massive arcing, but it was highly effective. My main problem was that the brushes melted somewhat with each shot, so they had to be continually adjusted. There was also a chance that the projectile got welded to the brushes and failed to exit... fun times.
Something you could look into is using a relatively low voltage (5-12v) across brushes to trigger an SCR or a relay which would control your 2nd stage capacitor bank. You'll have to tune your timing mechanically by adjusting the position of the brushes but it's a simple, legitimate design.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
I bet you could use a whisker switch to trigger an SCR pretty easily. My first multi-stage gun used two bits of bare wire that would get shorted by the projectile. This then triggered gas discharge tubes (like beefy flash bulbs) that dumped the cap energy into the coils.
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2 Stage Coilgun Trigger
