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i have built a few single stage coilguns in the past but there efficiency was only about 0.2% so i want to build a multistage coil gun with about three stages i am going to use igbt's to trigger the stages so i can turn them off when i want would this idea work
as shown in the picture below as the projectile blocks the infa red led and detector (blue) it triggers the coil but when the projectile is fully inside the coil (orange) and the ir detector detects ir again it terns the coil off
or is there a better way like it detects the projectile and you set the delay on when to switch it off
Registered Member #3792
Joined: Sun Mar 27 2011, 06:07PM
Location:
Posts: 136
You could start by looking at this link. Another Coilgun also has good information about triggering (click on the "Projectile Detection" link) that can be scaled for as many stages as required.
The usual approach for triggering MOSFETs or IGBTs is a 555 configured as a one - shot oscillator (so that it only gives one pulse for triggering) and a second one as a delay (where you can adjust the time delay between the initial trigger pulse and the actual output). Although all these can be very easily duplicated inside a microcontroller.
Keep in mind that triggering MOSFETs or IGBTs is a bit more difficult than triggering SCRs because of the fact that after you switch them ON you must also switch them OFF. That means a circuit that must either have a fixed trigger pulse length or it can track the projectile's position relative to the accelerating coil. SCRs only need to be switched ON to operate (and will be kept ON until the voltage between the cathode and the anode drops below a certain limit or reversed).
Registered Member #1525
Joined: Mon Jun 09 2008, 12:16AM
Location: America
Posts: 294
Josh what you posted will work just fine and is in fact the preferred method for triggering a coil with IGBTs. The method PSCG described will also work, but it's what you call "open loop" since it requires user input to guess the timing, whereas your method is "closed loop" meaning it knows exactly when to start and stop the pulse every time without user input since it can sense the projectiles position. It's more accurate and simpler to implement. It's the same method I've used very successfully in my 8 stage IGBT coilgun.
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multistage coilgun trigger
