Coilgun EM-3 ("Electric bow") / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Coilgun EM-3 ("Electric bow")

previous 1 2 3

Move Thread

LAN_403

DerAlbi

Thu Jan 07 2016, 11:15PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Hmmh. I am still not sure. Most people have only experience with bad designed coilguns where projectile instability occurs because they suffer from suckback so they actually rely on the barrel to guide the projectile at the end. As you can see in my videos the projectile tip is actually round (if not, then now i told you so

). I will not panic before i test this... also water is a bit different to air since it applys much more presure and turbulance.. but that only shortens the distance for visible effects.
Not that you might not be right, however i will keep in mind that the experience is based on bad designs. As long as no one has built a big gun yet, we cant verify.
Spinning the projectile is complicated. It puts enormeous stess to the guiding-system inside the coils. It might just cause more trouble than its solving. For now i just hope that the fundamental difference between pushing and pulling is on my side.

I think here that for your number 4 any lawyer opposing you would say that it is clear that the coil is guiding the projectile (via the magnetic field), and the second video shows quite clearly that it plays an active part in guiding the projectile.

The magnetic field is NOT the coil. If the guidance is done by magnetic field, then the coils not not active in the guidance only because its the source of the field. And even if they tell me that, then i just say: the coil issnt the source, but the current flow is. The first video only shows that the "missconception" is currently not mine

If there was a strong force towards a wall of the coil the air gap would have closed and wouldnt stay symetrically.
The second video shows how the projectile touches the coil, yes. But how did it go into the coil without mechanical guidance? If the coil as physical body would be responsible, then this would not have worked. The position got corrected by the magnetic field alone, then it was sucked in further (and yes in that case instable). So is the coil a barrel?

And dont mix up projectile length with projectile diameter (caliber).

The first video looks like a bullet is coming at you

Who cares. the coil stayed magnetized.. the projectile could never leave the coil

Karmaslap

Thu Jan 07 2016, 11:40PM

Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65

The flight characteristics are independent of the coilgun's design so long as they both spit the projectile out lengthwise. It's definitely not the best design. Look at shotgun slugs for high speeds- they are tapered in the front, and have grooves on them in the back so that they spin themselves. If a cylinder was fine, they wouldn't go through that much trouble.
(A cylinder is NOT a good shape, I just had trouble finding online where to direct you to to see that... because everyone knows it is a bad shape and so nobody even plays with it in air anymore)
If you just want your range to be 50m... who knows. I did see the rounded tip in the first video, but wasn't sure if that was just a weird perspective. Your guidance system is based on the detection of eddy currents and not photogates? Have you calculated energy losses to eddy currents in the projectile?

Spinning it before it shoots is difficult. putting grooves on it so it spins itself might be easier.

You can tell me that, but any opposing lawyer would not listen I think. The current flows through the coil, they generate the field that stabilizes the projectile.. so the coil is necessary. It isn't a typical barrel at all, but they might say that your teflon is a barrel?

woops, I mixed them. thanks.

DerAlbi

Fri Jan 08 2016, 02:22AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

The flight characteristics are independent of the coilgun's design so long as they both spit the projectile out lengthwise.

Nohohohooooo! Thats what i try to say for about 2 posts now

Bad designed coilguns that have any suckback effect going on accelerate the projectile lateraly instable! A bad coilgun therefore will spit out the projectile with more parasitic lateral momentum than a proper designed CG. This is important.
If you are far away from suckback, then you accelerate allways to the center of the coil. As soon as the projectile is perfectly in the middle of the col the projectile position is lateral unstable if the current hasnt allready stopped. so... Lengthwise is not euqal to Lengthwise.

Your guidance system is based on the detection of eddy currents and not photogates? Have you calculated energy losses to eddy currents in the projectile?

Thats a question for my own thread, but the short answer is that its way more complicated than that^^ The eddy current loss is not as important as the fact that there is one at all. And its not a guidance.. its a detection.

putting grooves on it so it spins itself might be easier.

No way. In a conventional gun, thats no problem. The additional friction is just holding back the gas that most likely will just build up more pressure in the mean time - this might even be beneficial. In a coilgun that friction is directly contributing to bad efficiency. You can not afford it in any way. If you want to spin it, spin it before the shot.
And...... "taofledermaus" on youtube is a nice channel to watch. but he is focussed on supersonic bullet design. but one thing i learned: even a smooth-bore-shotgun can shoot quite precise.

the current flows through the coil, they generate the field that stabilizes the projectile.. so the coil is necessary.

If you talk about whats necessary then everything is the barrel

Its also wouldnt work without the capacitors. that cant be the fact they nail me with.

but they might say that your teflon is a barrel?

Depends on what they define as "tubular". I guess thats another definition they just invent when its needed. I will try my best to make the inner design rail-like. Thats all i can currently do.

And sry Eugen, i know we are hijacking your thread

It just went that way...

Karmaslap

Fri Jan 08 2016, 06:34AM

Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65

Moving to your thread to reply, haha

previous 1 2 3

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob