Electromagnetic Launcher

[dknguyen]

however - the national high mag field guy said he can get 1 ton off of ten amps. but really teh equation - is that it? electromagnets are jus this totally dope energy efficient method of motion thats just getting ignored? help me out guys lets do this how do i build my mag launcher???

You're putting too much stake into current = magnetic field strength Think about it this way:

1. I have a 10cm diameter coil with 10 turns and I run ten amps through it.

2. I have a 10cm coil diameter coil with 10,000 turns and I run ten amps through it.

Do they generate anywhere near the same magnetic field just because their current it the same? Surely no. What's the difference? Obviously #2 one has more coils which also means much more voltage required to drive that same currents through the coils. That's a lot more power behind magnetic field #2.

Real life is much messier mathematically than teachers would lead you to believe and napkin equations do not cut it. With such simple equations you either need thousands or millions of them each covering a tiny part of the whole object (finite element analysis using computers) or they are making serious assumptions. In this case one them appears to be that the diameter of the coil is infinitesimal small relative to the length of the coil (i.e. the coil is much longer than it is wide). Things get messier near the ends.

Another issue might be saturation which doesn't seem to be accounted for in those equations.

 

[gophert]

The "L" term in the equation is the length of the coil. Fat wire make a long "L" term for a given number of turns. Ideally you want to concentrate the turns as close as possible.

 

[Q_CLD]

It's gotta be the permeability value for the core.

because if I do 1 layer of the coil with 5 turns - that makes the length (L) of the gap 0.0036576m (the height/diamter of the 7AWG magnetwire) that will make a coil of, ok lets make it a 1cm diameter iron core plus the 5 turns so; 10 x 0.0036576m + the 1cm core = 4.66cm wide and 3.66mm tall. and connect that to 10Amps - I still get a huge number for the force T value of = 3,417 T

 

[Q_CLD]

The "L" term in the equation is the length of the coil. Fat wire make a long "L" term for a given number of turns. Ideally you want to concentrate the turns as close as possible.

What do you mean? I have been thinking that L,the gap is the number levels in the coils i.e. if it's just 1 level of the wire w 5 turns the L would be the height/diemeter of the magnet wire. e.g. if I my N value is 10 - 5 turns on 2 levels my L value is 0.0073152m ~ 2 x the hight/diameter of the magnet wire.

essentially the length of the core

Right?

 

[Q_CLD]

hope my ( - ) and ( / ) in the last post aren't getting confused for arithmetic symbols, sry if so.

 

[dknguyen]

ideally id want a high number for U - it just seems like 10amps, 10turns, 1cm, w the 0.25 for permeability of iron gives an unrealistic amount of force. from above 1T can lift 6.3kg (13.889 lbs) 5cm


I mean if thats the facts - than Id LOVE LOVE LOVE to get my hands on 2cm of 0.00AWG wire (1cm thick) and attach it to a deep cycle marine battery blast it w 300Amps. (thin wire can't handle the amps)

however - the national high mag field guy said he can get 1 ton off of ten amps. but really teh equation - is that it? electromagnets are jus this totally dope energy efficient method of motion thats just getting ignored? help me out guys lets do this how do i build my mag launcher???

It's gotta be the permeability value for the core.

because if I do 1 layer of the coil with 5 turns - that makes the length (L) of the gap 0.0036576m (the height/diamter of the 7AWG magnetwire) that will make a coil of, ok lets make it a 1cm diameter iron core plus the 5 turns so; 10 x 0.0036576m + the 1cm core = 4.66cm wide and 3.66mm tall. and connect that to 10Amps - I still get a huge number for the force T value of = 3,417 T

Core saturation.

 

[dknguyen]

It's gotta be the permeability value for the core.

because if I do 1 layer of the coil with 5 turns - that makes the length (L) of the gap 0.0036576m (the height/diamter of the 7AWG magnetwire) that will make a coil of, ok lets make it a 1cm diameter iron core plus the 5 turns so; 10 x 0.0036576m + the 1cm core = 4.66cm wide and 3.66mm tall. and connect that to 10Amps - I still get a huge number for the force T value of = 3,417 T

Do you know what core saturation is?

 

[Q_CLD]

Do you know what core saturation is?

Im reading about it now - please explain!

 

[dknguyen]

Im reading about it now - please explain!

You can only stuff so much lines of magnetic flux into a core. Even if I had iron and wire that never melted, I can't just pump a million amps through something the size of my fist to make a super strong, super small electromagnet. Basically, how big something is limits how powerful it can be. Might be obvious but you're running into the specifics of it and the limitations of paper napkin calculations.

 

[Q_CLD]

ok core materials than?

but is the value listed in the wikapedia link with common material values what Id need to use for U?
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

 

[dknguyen]

ok core materials than?

but is the value listed in the wikapedia link with common material values what Id need to use for U?
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

U is not the problem. You have a paper napkin calculation that is giving you thousands of Teslas and (if you looked) the absolute highest saturation materials we have aren't above 3T. Take what I say with a grain of salt though because I am not a magnetics guy.

 

[gophert]

What do you mean? I have been thinking that L,the gap is the number levels in the coils i.e. if it's just 1 level of the wire w 5 turns the L would be the height/diemeter of the magnet wire. e.g. if I my N value is 10 - 5 turns on 2 levels my L value is 0.0073152m ~ 2 x the hight/diameter of the magnet wire.

essentially the length of the core

Right?

Nope, you are confusing it with "Wraps". If your wire is 0.5mm and your solenoid is 50 mm long, you can get 100 turns per wrap. If you need 200 turns, you'll need two wraps, turns = 200 and L = 50.

Also, the more wraps you go, the less effective each wrap is because it is further from the core.

 

[Q_CLD]

So basically this has been a bunch of people who don’t know anything about electromagnets telling a another guy who doesn’t know anything about electromagnets he’s wrong - save that **** for reddit.

 

[gary350]

Have it your way.

 

[Q_CLD]

PLEASE ONLY COMMENT IF YOU HAVE ACTUAL KNOWLEDGE OF WHAT EQUATION TO USE TO FIND THE FORCE OF AN ELECTROMAGNET IN REGARDS TO COIL DESIGN.

Amps
Number of turns
Core material

Those factors will effect the field strength.

 

[gophert]

PLEASE ONLY COMMENT IF YOU HAVE ACTUAL KNOWLEDGE OF WHAT EQUATION TO USE TO FIND THE FORCE OF AN ELECTROMAGNET IN REGARDS TO COIL DESIGN.

.

It doesn't work that way here. People say what people say. Welcome to the community.

 

[gophert]

So basically this has been a bunch of people who don’t know anything about electromagnets telling a another guy who doesn’t know anything about electromagnets he’s wrong - save that **** for reddit.

Who was that statement for?

 

[Q_CLD]

This obviously not useful.

 

[rjenkinsgb]

I NEED ACTUAL HELP!

Take a step back and look at the overall problem...

To launch an object via an electromagnet (which is working as a solenoid, in this application), it needs either to be an iron item below the solenoid coil and pulled towards it when power is applied, or a magnet already inside it that will be repelled by the field of the solenoid coil.

An iron core already in the coil makes a stronger field if simply lifting something, but you cannot "fire" anything through it.
The only way that could work is if you had a kind of radial arrangement of coils and cores around the barrel, arranged so the same pole of each core pointed to the same point in the centre of the barrel.


The other problem with an iron projectile is that the solenoid is trying to pull it to the centre of the coil, as long as power is applied.
You need a very strong pulse of current to get the initial pull towards or in to the solenoid, but the current must cut off and the magnetic field die away before the object gets past the centre of the coil, or it will be slowed down again and pulled back.


A coil is an inductor; it resists changes in current flow.
An air-cored inductor has the fastest rise and fall; any iron core slows that dramatically as it increases the inductance.

The way to get a fast current rise and cutoff is to use a capacitor charged to a high voltage, switched to the inductor.
The capacitor discharges and gives a short, high current pulse.

The relative magnetic strength of a coil is given by "ampere turns"; eg. a ten turn coil with 100 amps is the same strength as a 1000 turn coil with one amp current.
The 1000 turn coil will have 10,000 times the inductance, though (it's the square of the turns ratio) so in proportion a very slow current rise. Low turns and extremely high currents are needed for a true short-duration pulse.


There are many "coil gun" designs on line and I doubt you will find any (or any effective ones) that use iron-cored coils.

Edit - This is an example DIY coil gun that would do what you need, if mounted upright.. It may be a bit over powered (or not..) but making it less so is easy - just reduce the number of capacitors.
https://www.instructables.com/id/Magnetic-Coil-Gun/

 

[Dr_Doggy]

your advice has been sound
the core is the bullet .. which is impossible to calculate mostly cos it moves alot

why are you doing this?

2)the local gun store is too far:
a GOOD coilgun is not much better than a bb gun, thats with multi-coils and precision triggering ... there is more factors than you can imagine for the best most efficient ... the reason the military does not use them is cos they are weak. .. but what the military does use is its more powerful/larger/expensive cousin ... the rail gun

1)you just want to see a working model?
if you just want something work wrap a coil and put it on some caps... not rocket science yet..

if you want to tweek it to max efficiency you will need more tools like a scope and chronograph ... and then try a few test coils .. after that if you want more power increase the volts ... if your coil needs a longer charge increase the Farads in the capacitors

here is an example of my coilgun ... it charges two 1000uf capacitors to 400volts
i think it uses 22 or 28 guage but that was a bit too small since it fried after about 100shots
this coil is able to sling a nail across a 20ft room but not powerful enough to tear the paper target ... kinda like an elastic band and a paper clip ... i wraped it with a chunk of wire i found at x length ... not sure the turns count either didnt do it .... nor did i wrap the coil evenly


you need to realize that dc magnets and slow charging coils are bad for a coilgun since if the magnet is still charged when the bullet goes past it it will pull the bullet in and slow it down which is why you need higher volts for faster spikes ... having said that 400v/0.1 ohm (rough calc) is 4000amps ... but that is only for a very very short time in my small coil ... i too was supplying my coilgun with a Li battery ... but that battery is what runs the boost converter to bring the volts to 400.

if you visit the coil builders they provide info on what they used for their coiltypes and cap banks used based on their barrel sizes


ALSO:
FIND THE FORCE OF AN ELECTROMAGNET
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magcur.html

but that is only a small chunk of the physics needed to calculate your gun out