• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Electromagnetic Launcher

Thread starter #1
I am putting together an induction launcher. I need help with a couple things with the design of the electromagnet.

Mainly Need help with the math:
The goal is to launch(NOT levitate) an object that is 3x the weight of the electromagnet 20cm high.

I'd like to use the 6000mAh lipo battery I already have if possible (so 6Amps)

I found 7 AWG square magnet wire, that’s the thickest I found in small consumer size quantities.
diameter: 0.144in which is 0.0036576m
weight: 15.87ft of this wire weighs 1lb
reference: https://mwswire.com/wp-content/uploads/2016/10/Copper-Magnet-Wire-Data.pdf

For the core; 5mm diameter and made of closest to pure iron I can get or better/easier to get.
reference: see section on 'Values for some common materials' https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials
This will help with the magnetic permeability variable I've seen in electromagnetic field strength equations.

With these above set values I believe the last thing I would need to know is the number of turns in the coil and the length of the "gap" - with my best guess means the length of the core? or how many levels in the coil(i hope Im describing that correctly).

It seems I'll have to guess and check from there, i.e. the weight will be determined by the number of turns and length the gap.


What equations do I use?

I found this site for calculating the length of wire: https://www.daycounter.com/Calculators/Coil-Physical-Properties-Calculator.phtml
Which will be helpful in determining the weight of the coil.

For electromagnetic field strength equations;
I found this video which I think is wrong:
AND this video which is maybe right, but IDK:

Then there is the question of the force T(teslas) how much force is even needed to launch(NOT levitate) 3x the weight of the electromagnet 20cm - I do not know where to find an equation for this.

AND if 6Amps isn't enough - than what battery?
 

alec_t

Well-Known Member
Most Helpful Member
#2
Welcome to ETO!
1) You are confusing mAh with mA. A 6000mAh battery is not limited to a current of 6A. It can, in theory, provide 6A for 1h, or 12A for 30 minutes, or 2A for 3h, etc.
2) I doubt you will be able to bend 3.66mm diameter wire closely around a 5mm diameter core.
3) I believe (I haven't done the maths) that a core that size will become magnetically saturated at a turns-current value much less than that needed to levitate, yet alone launch, anything approaching the weight of the coil.
4) What exactly do you mean by "launch"?
5) How are you proposing to get a single elctromagnet to launch anything? A magnet would attract, not repel, a ferromagnetic thing.
 
#3

dknguyen

Well-Known Member
Most Helpful Member
#4
So, you -definitely- need a capacitor bank to deliver enough instantaneous current to move anything of significant mass.
In addition to this,

LiPo peak discharge rate is listed by C-rating. So if it's 10C, that means it can "safely" discharge a current that is 10x the current rating that would drain it in one hour (i.e. ten times the mAh rating) which would be 60 amps for a 6000mAh battery. Be aware there is a lot of marketing in those C-ratings so they are NOT continouous ratings and I would not believe any rating above 30C. Also be aware that high C-rating LiPos make compromises and have shorter charge cycle lifetime than those with lower C-ratings.
 

gophert

Well-Known Member
Most Helpful Member
#5
I am putting together an induction launcher. I need help with a couple things with the design of the electromagnet.

Mainly Need help with the math:
The goal is to launch(NOT levitate) an object that is 3x the weight of the electromagnet 20cm high.

I'd like to use the 6000mAh lipo battery I already have if possible (so 6Amps)

I found 7 AWG square magnet wire, that’s the thickest I found in small consumer size quantities.
diameter: 0.144in which is 0.0036576m
weight: 15.87ft of this wire weighs 1lb
reference: https://mwswire.com/wp-content/uploads/2016/10/Copper-Magnet-Wire-Data.pdf

For the core; 5mm diameter and made of closest to pure iron I can get or better/easier to get.
reference: see section on 'Values for some common materials' https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials
This will help with the magnetic permeability variable I've seen in electromagnetic field strength equations.

With these above set values I believe the last thing I would need to know is the number of turns in the coil and the length of the "gap" - with my best guess means the length of the core? or how many levels in the coil(i hope Im describing that correctly).

It seems I'll have to guess and check from there, i.e. the weight will be determined by the number of turns and length the gap.


What equations do I use?

I found this site for calculating the length of wire: https://www.daycounter.com/Calculators/Coil-Physical-Properties-Calculator.phtml
Which will be helpful in determining the weight of the coil.

For electromagnetic field strength equations;
I found this video which I think is wrong:
AND this video which is maybe right, but IDK:

Then there is the question of the force T(teslas) how much force is even needed to launch(NOT levitate) 3x the weight of the electromagnet 20cm - I do not know where to find an equation for this.

AND if 6Amps isn't enough - than what battery?

Please alert the media when you can launch anything more than 2 meters.
 

shortbus=

Well-Known Member
#7
For the core; 5mm diameter and made of closest to pure iron I can get
I may be wrong, but from the little I've read about these they don't use an iron core, since that would just make it an electromagnet. They seem to use a nonmagnetic core. A search online give a lot of information about doing what you want.
 
#9
TYPING IN ALL CAPS IS THE EQUIVALENT OF YELLING!
(Which is not polite, btw)

How about this: How about you read through the resources provided to you and come back with specific questions about it.

We will be more than glad to help you. :)
 
Thread starter #10
I was told high amps and thick wire will give me a short but strong field, Thus to "launch" 7AWG is the thickest I can find for small consumer quantities. I doubt I need a meter of it.

As for the core - I was told it would bend by the manufacturer. IF not iron (which has a high permeability) than what should I use - looking at the equations in the youtube vids it says a core w a high permeability is what I need.

AND idk who told you electromagnets ONLY attract but that is incorrect. ALSO - as for getting something to launch 3 meters and call the media - huh?
PLEASE NO MORE TROLLS - I NEED ACTUAL HELP! willing to pay - not to construct and manuacture for me, just walk me through the parts and how to connect them.
 

gophert

Well-Known Member
Most Helpful Member
#11
SO. WITH ALL OF THIS IS ANYBODY WILLING TO WALK ME THROUGH IT!
Look above, the ball appears to be in your court. If you want to play, you have to return some serves. Answer the open questions and let us know your budget and give us some insight into your skill level in electronics.
 
Thread starter #12
I guess I would first like to focus on the design of the electromagnet. NOT the battery for now. What equation should I use to determine the amount of force? I have 2 youtube vids w/ 2 different equations - and neither may be what I need. I think figuring this out is a good first step.

I will have to play w the numbers to get the correct force to weight ratio - but the field repel force strength equation is first.

that ok?
 

dknguyen

Well-Known Member
Most Helpful Member
#13
I guess I would first like to focus on the design of the electromagnet. NOT the battery for now. What equation should I use to determine the amount of force? I have 2 youtube vids w/ 2 different equations - and neither may be what I need. I think figuring this out is a good first step.

I will have to play w the numbers to get the correct force to weight ratio - but the field repel force strength equation is first.

that ok?
Before you calculate the force the coil will produce, have you calculated how much force you actually need to launch the mass to your desired height (or rather, what velocity you must accelerate the mass to. The actual force will change on how much time (i.e. rail length) you have to accelerate the mass, and of course how much mass there actually is.
 
Last edited:
Thread starter #14
Before you calculate the force the coil will produce, have you calculated how much force you actually need to launch the mass to your desired height?
True - however, the weight to be lifted will be determined by the weight of the electromagnet.

So I think I need to see how much force (T) I can get with (I) Amps and (N) turns and the (L) length of the core which the core is wound around. - maybe? so like I'll play with the number, e.g. 16 turns is x lbs and with whatever amps and whatever length, etc -however that is based off of what I saw from the youtube vids, which may not even be right.
 

gophert

Well-Known Member
Most Helpful Member
#15
I guess I would first like to focus on the design of the electromagnet. NOT the battery for now. What equation should I use to determine the amount of force? I have 2 youtube vids w/ 2 different equations - and neither may be what I need. I think figuring this out is a good first step.

I will have to play w the numbers to get the correct force to weight ratio - but the field repel force strength equation is first.

that ok?

First you need to know the velocity needed to reach the desired height.

Then you need to decide how much distance you allow to accelerate the object (by applying a force).

Then you need to decide how much the object weighs.

Finally, you can calculate how much energy you need to get the object to the desired height (to a new potential energy).

Then work back, again,
force = mass * acceleration.

And how you can get the "work" applied to the object in the available acceleration distance to get the impulse you need to launch the object.
 

alec_t

Well-Known Member
Most Helpful Member
#16
What equation should I use to determine the amount of force?
No single equation can give you the force. The force exerted by a solenoid depends not only on the construction and current but also on the material of the object it is trying to move and the distance of the object from the solenoid. The force required to move an object depends on the mass of the object and the desired acceleration; also on opposing frictional forces which need to be overcome.
 

gophert

Well-Known Member
Most Helpful Member
#17
Now, if the magnet is the projectile, you will need some calculus to determine the rate of change of magnetic field possible with increasing weight of the wire.
And some additional calculus since the force will not be constant as the electromagnet leaves the magnetic field that is repelling it.
 

dknguyen

Well-Known Member
Most Helpful Member
#18
True - however, the weight to be lifted will be determined by the weight of the electromagnet.

So I think I need to see how much force (T) I can get with (I) Amps and (N) turns and the (L) length of the core which the core is wound around. - maybe? so like I'll play with the number, e.g. 16 turns is x lbs and with whatever amps and whatever length, etc -however that is based off of what I saw from the youtube vids, which may not even be right.
If you're designing from both ends (there are other engineering and math problems like this too where two different things are dependent on each other simultaneously. Like propellers: the propeller moves the plane but how much force it produces depends on how fast the plane is already moving so how on earth are you supposed to figure out how fast the plane moves?) then you might have to take an initial stab in the dark and iteratively work from there. Similar to taking an initial guess for an answer to a math problem with two dependent variables and then repeatedly plugging your most recent solution back into the equations and solving it until the values of the two variables both converge to their own stable value. That is, just start designing a magnet on paper and calculate out it's weight then calculate if it can handle the power required to launch something three times it's mass. From there, plug the solutions back and forth into each other into the equations until you get something that satisfies all the equations.

A good starting point is probably just designing an electromagnet with the construction and size that would be easiest (or that you prefer) to build with the materials you can most easily get ahold of that you think might work just based off of gut feeling.

That said, do you know for a fact that launching the mass 3x the weight of the launcher is possible, even 20cm? Pretty much every gun (railgun, cannon, or firearm) launches something much smaller than it's own weight. Do you already know for a fact that real materials can handle the power and magnetic fields required for what you want?
 
Last edited:

gophert

Well-Known Member
Most Helpful Member
#19
Why are you thinking of 7awg? The weight will really obstruct your goal of launching. The short impulse time means you can use much thinner wire because the wire has little time to heat in such a short time.

Let's look at 22 gauge wire. One meter is about 0.05 ohms. At 12V and one meter, you can get 235A flowing according to ohms law. Your battery may not be able to pump that much current because of internal battery resistance. If it can, great, if it cannot, you can use a bank of capacitors in parallel. Hopefully your bank of resistors (in parallel) will have equivalent series resistance much below the resistance of the wire.

Note that a mere 22 gauge wire can handle up to 550 A for 32mSec.

Your question is quite complicated and trial and error is the best answer but I would start my looking at the current burst you are able to achieve with your budget (battery or capacitor bank), find an iron core that can handle that current without saturating magnetically, then wind enough wire around it to achieve your current target. Fewer turns are generally better because more turns means your total impedance will increase beyond your DC resistance as inductance increases (I.e. more turns) so you will have less effective current flow.
 
Thread starter #20
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.
 

Latest threads

EE World Online Articles

Loading

 
Top