Electromagnetic Launcher

[dknguyen]

7awg because that is the thickest I could find in small quantities for consumers.

A quote from the head of the high mag field lab; you can make a fast pulse with fat wire but the field will be low, or you can make an intense pulse with thin wire but it will take some time to reach maximum.

And thats what I want short hard punch to "launch" an object NOT levitate.

How does a low field equal a hard punch? Sounds like a short light punch to me. You can still launch things if you apply a lower force over a longer period of time. Just look at what a ballistic missile does compared to a cannon.

 

[Q_CLD]

sounds good -you tell me!

 

[Q_CLD]

The guy at the high mag field lab was telling me to get thick wire and attache it to a car battery basically.

 

[dknguyen]

Yes - https://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launch_System

I still don't see part where the launcher weighs less than the payload.

 

[Q_CLD]

I DONT need to lift a ton though. the initial punch needs to send the object 20cm for so though. something as light as possible. Varsity tutors says they'll hook me up w a physics guy to walk me through this for $75/hr as for my budget and knowledge, Its a kids science fair project and I got A's in physics and calc but thus stuff never came up to teh extent I need.

 

[dknguyen]

I DONT need to lift a ton though. the initial punch needs to send the object 20cm for so though. something as light as possible.

None of that matters though since since you said you implied you needed quite a bit more than a 3:1 force -to-weight ratio so absolute weight is irrelevant. I'm just wondering whether it's possible or not.

 

[Q_CLD]

YES IT IS POSSIBLE - e.g. a 1T earth magnet can lift 6.3kg 5cm -

6 lbs levitation for a small magnet. That's 6 lbs over the 1 cm^2 area of the magnet. Add more magnets and more area, and you lift more weight.


With an area 1000 cm^2 there's 1,000 magnets underneath. 1000 x 6 lbs = 6,000 lbs = 3 tons...





1 T is about the limit. Many scientists are working hard to make stronger, lighter, bigger magnets for motors and generators.





calculate the force from here: https://en.wikipedia.org/wiki/Force_between_magnets , see the section on force between two cylindrical magnets --- in this example of cylindrical magnets the magnetization (mu_0 M) = 1 tesla, so M = 1 tesla / mu_0 = 7.96 x 10^5 A/m because mu_0 = 4 pi x 10^-7 N/A^2.





one magnet with north pole facing up, other magnet above it with north pole facing down.


the density of permanent magnets is approximately 10,000 kg/m^3, the mass of each magnet is about 7.85 x 10^-3 kg = 7.85 grams.





use the wikipedia equation to solve for the levitation height x if you make the levitating force equal to the gravitational force = 7.85 x 10^-3 kg x 9.8 m/s^2 = 7.7 x 10^-2 newtons. I get about 5 cm for levitation height by using the point dipole approximation (which does not account for tipping - you'd have to do the levitation in a tube). I also get about 62 N for the force needed to push the levitating magnet down to the magnet on the table, i.e. the maximum load that can be suspended is about 6.3 kg.





Now, if you use a 1 cm diameter, 1 cm tall superconductor for one of the magnets, and it becomes perfectly diamagnetic under the action of the other permanent magnet, you will get the same answer as for two permanent magnets above. This is because the superconductor responds to the permanent magnet by flowing current to oppose the permanent magnet's field, see https://simple.wikipedia.org/wiki/Lenz's_law . Perfect diamagnetism means 100% of the field is opposed, i.e. exactly like the two permanent magnets. But the currents only flow to the maximum level induced by the permanent magnet








Force depends on the flux density of the magnets.


The levitating pressure (force per unit area) scales as the square of the flux density and inversely with the levitation height.


Stronger magnets, more force. Heavier object, less height.





you can make a fast pulse with fat wire but the field will be low, or you can make an intense pulse with thin wire but it will take some time to reach maximum.

 

[gophert]

Wh don't we focus on current values that your battery is able to supply. Let's say, 60 amps for a short burst.
That means 7 gauge wire is stupid big. Let's focus on common 22 to 24 gauge hookup wore that is commonly available and easy to wrap around a reasonably small iron core.

 

[gophert]

you can make a fast pulse with fat wire but the field will be low, or you can make an intense pulse with thin wire but it will take some time to reach maximum.

Fat wire is a relative term. Many magnets and magnetic devices are wound with 40 gauge wire so a 22 gauge looks huge next to 40 gauge.

 

[Q_CLD]

Thank you guys so much - I do feel I need clarification on the equation for repel force of an electromagnet and how that applies to the design of the electromagnet. are the equations from the YouTube vids correct? which one or what instead.?

I think if I plug and chug and play around with the equation I can get what I want.
Thank you

 

[Q_CLD]

he's the head of the national high field lab - he said thick wire and lots of amps. TROLL no more please gophert

 

[dknguyen]

Thank you guys so much - I do feel I need clarification on the equation for repel force of an electromagnet and how that applies to the design of the electromagnet. are the equations from the YouTube vids correct? which one or what instead.?

I think if I plug and chug and play around with the equation I can get what I want.
Thank you

I don't see the problem. Both videos show the same equation. u = u0 * ur. What's easier to remember? That steel has a permeability of 5 * 10-3 T-m/A? Or that it's just 200x that of free space?

 

[gophert]

he's the head of the national high field lab - he said thick wire and lots of amps. TROLL no more please gophert

As I said above, 22 gauge wire can handle 10x the amps that your battery can output. Thick is thick but 7 gauge is reduculous if you are trying to wrap it around a core. Good luck with your project.

 

[Q_CLD]

In the first vid:
B = force in Teslas (T)
U = magnetic constant of iron is 0.25 see values common materials
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials
N = number of turns
I = Amps
L = length of the gap

B = ( U )( N ) ( I )
L

in the second vid:

B = ( U ) ( N/L ) ( I )

is that some how the same thing because -

e.g. let's say:
U = 0.25
N = 10
I = 10 Amps
L = 0.1m

vid 1's equation = 2500 T
vid 2's equation = 250 T

or am i wrong on both - is my order of operations correct? are these really the right equations?

 

[Q_CLD]

it won't let me out the 'L' under the (U)(N)(I) do show its the denominator for equation 1

 

[dknguyen]

Yes, those are the same thing. I get the same answer for both

You are probably not using brackets liberally enough when you enter it into the calculator so things are ending up in the denominator when they are supposed to be in the numerator. Use brackets, liberally. Don't let the calculator make assumptions about how to group things together. I have no idea how you introduced an extra factor ten to get 2500T.

You need to go full stop and figure out how to enter things into the calculator before you go any further. I saw this issue all the time when I was tutoring high school students. It's a lot easier when I can sit there and watch them punch things in.

 

[Q_CLD]

AND either way 250T is a lot of force so that can't be right.

 

[dknguyen]

AND either way 250T is a lot of force so that can't be right.

Might be because you used pure iron. Don't most people use steel? It's a lot less.

 

[Q_CLD]

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???

 

[Q_CLD]

my guess is I have the permeability U value wrong - any insight there?