New User, a quick (mabye?) question about coilguns.

[Crated]

I've been seeing a lot of coilgun videos over the past 2 years. I'm addicted to getting/making fun new toys.

The videos and stuff I've seen have all had several coils lined up in sequence. My understanding is that these coils activate sequentially using sensors to detect the projectile. My question is, are those small coils actually being used in the best way? I'm not an expert on magnetic fields or electronics, so forgive my ignorance.

I had a thought I wanted to share, what if each coil was set up so they could connect with the other coils and disconnect/turn off after the projectile has passed that point. The end result I'm thinking of is a magnetic field that starts by covering the whole barrel but shrinks as the projectile get closer to the front of the barrel and the initial coils deactivate/disconnect.

I seriously doubt this idea doesn't have issues, but I was curious and decided to write it down and ask before it joined the rest of my forgotten ideas.

[davekni]

I had a thought I wanted to share, what if each coil was set up so they could connect with the other coils and disconnect/turn off after the projectile has passed that point. The end result I'm thinking of is a magnetic field that starts by covering the whole barrel but shrinks as the projectile get closer to the front of the barrel and the initial coils deactivate/disconnect.

If I understand correctly, this might simplify control a bit (single turn-on time for all coils).  Each coil still requires individual turn-off, so I'm not sure it's much additional work to have individual turn-on times too.
The down-side that comes to mind is more power loss (more heating) in later coils.  One limiting factor for final projectile speed is coil heating (causing insulation damage if too hot).  This simplification might reduce speed.

Have fun building and experimenting!  BTW, I've played with single-stage coil guns only, so no personal experience with multi-stage units.

[Crated]

The issue is connecting/disconnecting with multiple coiled layers. Not sure exactly how to go about it, but I like tinkering. I’m gonna read up some more before I start trying to make an actual coilgun.

For the moment, I’m just gonna grab some supplies and fire up my 3d printer and mess around with different coil designs. See what works and doesn’t.

Thanks for the reply davekni

[Crated]

I’ve ordered some iron filings and steel bbs to help see the fields. I know there’s magnetic film but I don’t know if that’d help. Any recommendations? Make an array of very small electromagnets and measure the effect the test coil has on them?

[davekni]

Any recommendations? Make an array of very small electromagnets and measure the effect the test coil has on them?

Simulation is the easiest way to visualize fields and to compare different designs.  FEMM is a free tool that I heard about here on the forum.  Requires some learning, but very useful.  I'm quite happy to have found that tool.
Iron filings may be useful for getting a general understanding of field patterns around a solenoid coil.  There are plenty of pictures available showing that too (in text books, on line, etc.).
For physical experimenting, I'd suggest using your real intended projectile.  Run DC current through a coil, as high current as possible without excessive coil heating.  Measure force on projectile at varying positions approaching and inside coil.  This DC testing will miss eddy-current (inducted current) effects, but still be a good starting point.  (Presumes you are using a ferromagnetic projectile.)