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Using Arduino => General Electronics => Topic started by: tjones9163 on Nov 10, 2019, 05:23 pm

Title: coil gun question
Post by: tjones9163 on Nov 10, 2019, 05:23 pm
Hello,     below I will have 2 pictures below,

First) Is an enameled wire that I have wrapped around a plastic tube with 3 layers and each layer has about 120 turns, so 360 turns total. When i hook this up to my power supply through a basic push button ( that I learned not to press with my finger lol) and this draws the max 5amp from my power supply at around 18v.

Second) The other object is a 12v 250ma electromagnet.

I have several questions,

-In my wrapped enameled wire setup I noticed that it only works as an electromagnet when I place a small screw inside the tube and it doesn't work when I try it on the outside. ( I understand that the magnetic flux gets concentrated  inside the tube),
but how is it that the second picture the store-bought 12v electromagnet works better as a contact Electro-magnet and the screw will stick to the side of it.
Is it the method it was wrapped?

-If I am wrapping from left to right in a clockwise manner. When I am finishing the first layer and i am all the way to the right, I keep the wire tight and cross it all the way to the left side in one big turn, then start wrapping from left to right once again. Is that correct? I am pretty sure.
(https://forum.arduino.cc/index.php?action=dlattach;topic=645640.0;attach=332328)
(https://forum.arduino.cc/index.php?action=dlattach;topic=645640.0;attach=332330)

Title: Re: coil gun question
Post by: wvmarle on Nov 10, 2019, 05:48 pm
Do look up how magnetic fields look like. The field lines are big circles - concentrated in the core of your magnet, fanning out on the outside.
That store bought battery appears to have a metal case around the coil, I assume iron or a magnetisable stainless steel, that case will also concentrate the magnetic field.
Title: Re: coil gun question
Post by: JCA34F on Nov 10, 2019, 06:18 pm
Did you measure the resistance of your coil? Did you measure the resistance of the store bought E-magnet?
What was the difference? The E-magnet coil is wound on a core of soft iron (magnet iron) that has high magnetic permeability, what about the core in your coil? Your coil might work as a radio antenna but never as a magnet.   :)
E-magnet (https://en.wikipedia.org/wiki/Electromagnet)
Title: Re: coil gun question
Post by: tjones9163 on Nov 10, 2019, 11:14 pm
Did you measure the resistance of your coil? Did you measure the resistance of the store-bought E-magnet?
What was the difference? The E-magnet coil is wound on a core of soft iron (magnet iron) that has high magnetic permeability, what about the core in your coil? Your coil might work as a radio antenna but never as a magnet.   :)
E-magnet (https://en.wikipedia.org/wiki/Electromagnet)
That is a good question, i forgot about the resistance.
I measured the home-made one around 4 OHMS and the store-bought at 50 OHMS, which probably suggests that the store-bought it has more turns of wire.
But, where my home-made coil might not act like a magnet like the store-bought, my version wrapped around a tube is how a lot of basic coil guns are made, so i guess it only has much use when something is inside the air-core coil.
Title: Re: coil gun question
Post by: tjones9163 on Nov 10, 2019, 11:45 pm
Another question, in the picture below, shows that magnetic lines of flux for an air-core coil, just like my home-made setup.
My question is, because of the right-hand rule and the flow of current from positive to negative. Does it matter which side I enter in the screw that I want to project? As of now, the experiment works now on either side I enter the screw when I power it will get attracted to the center. Is one side going to attract the object quicker?
(https://forum.arduino.cc/index.php?action=dlattach;topic=645640.0;attach=332379)
Title: Re: coil gun question
Post by: herbschwarz on Nov 10, 2019, 11:54 pm
It will matter only if the screw is magnetized.
Title: Re: coil gun question
Post by: Idahowalker on Nov 11, 2019, 12:08 am
I would start off with 1 coil, narrow in physical width that can be used to suspend an object; like a self stabilizing camera lens.. Once you got that ability, you'd want to duplicate those coils and stack-em on top of each other. Once you get 2 coils you'll want to learn how to manipulate the fields so that you can move the suspended object from 1 coil to the next. Once you are able to move the object from 1 coil to the next, you'll use a stack of coils, with the object suspended between the coils center, move the object up and down the length of your coil stack, slowly. When you have established control of the object suspended in the coils field, you'll then want to 'shoot' you object with a fast signal and blah, blah, blah.

But first, you need to learn how to suspend an object in the narrow width coil.
Title: Re: coil gun question
Post by: raschemmel on Nov 11, 2019, 03:32 am
You might want to use a cap to measure the inductance of both of them (https://www.testandmeasurementtips.com/how-to-measure-inductance/).

Title: Re: coil gun question
Post by: tjones9163 on Nov 11, 2019, 05:07 am
I would start off with 1 coil, narrow in physical width that can be used to suspend an object; like a self stabilizing camera lens.. Once you got that ability, you'd want to duplicate those coils and stack-em on top of each other. Once you get 2 coils you'll want to learn how to manipulate the fields so that you can move the suspended object from 1 coil to the next. Once you are able to move the object from 1 coil to the next, you'll use a stack of coils, with the object suspended between the coils center, move the object up and down the length of your coil stack, slowly. When you have established control of the object suspended in the coils field, you'll then want to 'shoot' you object with a fast signal and blah, blah, blah.

But first, you need to learn how to suspend an object in the narrow width coil.
when you say 1 coil, do u mean one wrapped layer or 1 whole coil? In my example I am using a plastic pencil cap which is pretty narrow in width, Also when you say suspend an object, do you mean inside the pencil cap when i apply voltage to the coil to make something like a screw stick to the inside of the coil in the cap. Because that i can do now. Thanks
Title: Re: coil gun question
Post by: tjones9163 on Nov 11, 2019, 05:08 am
You might want to use a cap to measure the inductance of both of them (https://www.testandmeasurementtips.com/how-to-measure-inductance/).


do I need an oscilloscope to do this experiment?
Title: Re: coil gun question
Post by: raschemmel on Nov 11, 2019, 05:27 am
You can probably use Nick Gammon's
Frequency counter sketch. You can use a
Schottky buffer to covert the signal to
a squarewave.
Title: Re: coil gun question
Post by: raschemmel on Nov 11, 2019, 05:28 am
You can probably use Nick Gammon's
Frequency counter sketch. You can use a
Schottky buffer to covert the signal to
a squarewave.
Title: Re: coil gun question
Post by: Idahowalker on Nov 11, 2019, 09:25 am
when you say 1 coil, do u mean one wrapped layer or 1 whole coil? In my example I am using a plastic pencil cap which is pretty narrow in width, Also when you say suspend an object, do you mean inside the pencil cap when i apply voltage to the coil to make something like a screw stick to the inside of the coil in the cap. Because that i can do now. Thanks
A lens stabilizer.
Title: Re: coil gun question
Post by: herbschwarz on Nov 11, 2019, 03:28 pm
The magnetizing force is proportional to
Ampere Turns per Inch. You do not have
to know the Inductance of the coil.
Herb
Title: Re: coil gun question
Post by: raschemmel on Nov 12, 2019, 01:47 am
I said "might" need to know...
Title: Re: coil gun question
Post by: MarkT on Nov 12, 2019, 03:13 pm
The magnetizing force is proportional to
Ampere Turns per Inch. You do not have
to know the Inductance of the coil.
Herb
The magnetizing force is equal to the amp-turns per _metre_ by definition, use SI units !!

Flux density inside a solenoid is B = µH, where µ is the permeability and H is the magnetizing force in A/m. (yes I know it looks like microhenries but this is an equation not a value!)

The coil is about 4cm long with 360 turns carrying 5A.  Therefore H = 5 x 360 / 0.04 ~= 45kA/m, and since
µ0 = 4π*10^-7, B ~= 56 millitesla

The electromagnet formed on an iron core has a far higher permeability due to the iron, the field could be upto 2 tesla max (saturation point of iron).

Pwoerful coil guns need high flux densities, only achievable by pulsing very high currents from a high voltage capacitor through a coil of fairly low inductance - more turns will not help, more volts will.  There are various dangers in constructing one, ie high voltage, exploding contacts and wires, projectiles.

Less powerful ones can benefit from iron cores as the peak magnetic field is lower, but the high inductance will limit speed attainable.