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Selectively magnetized (hemi)sphere Answered

Hi everybody!

I'm looking for a way to construct a hemisphere,
- maybe 1.5" to 2" in diameter
- ideally with no moving parts
- where any of a number of areas on the surface could be magnetized at will

I thought of having an array of tiny electromagnets starting from middle and radiating to under the surface, but frankly, that would take a long time, and I figure there would be insulation issues.

Any suggestions?

Discussions

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Toga_Dan

4 years ago

http://www.rcgroups.com/forums/showthread.php?t=1169548

scroll to bottom of page.

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Toga_Dan

4 years ago

I just wound a couple electromagnets on cores of steel brads. Diameter: a wee bit over 1/16" . Length less than 1/2". I havent powered em up yet. Pictures to follow.

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Toga_DanToga_Dan

Reply 4 years ago

These 2 electromagnets were wound onto 19 GA brads. The wire is from a transformer I pulled apart. 1 mag has about 10 feet of wire. The other has about 12. I wound them using a drill. The wire is glued down with fingernail polish. I would have used superglue, but didn't find it. I haven't applied power yet.

Tiny electromag.jpg
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Toga_DanToga_Dan

Reply 4 years ago

Update: Applied voltage to mag. 1.5 volts-no effect detectable. (trying to pick up a brad of the same size) 4.5v- no effect detectable.

Got out the ohmmeter. Coil reads ~500 ohms. Ok. continuity proven.

9v applied. Coil starts to smoke. Fingernail polish bubbles. Although the mag holds a brad up, that brad stays when power is disconnected. It's now glued to the mag with melted polish. :P

Mag smokin 9v.jpg
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drmabToga_Dan

Reply 4 years ago

:) Thanks for testing, I was about to make a few myself.

Instead of using polish to glue the wire down, have you tried to jam the end in the drill head?

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Toga_Dandrmab

Reply 4 years ago

I thought about doin that, but the wire I used is about as fine as a human hair. I expect the drill chuck might break it. Even if it merely scored the wire, that would be a weak point to break or burn out.

By comparison, Before winding wire, I wound thread on the same size brad. It took about 4 feet of thread to make up a coil of the same diameter and length. It took about 10 feet of wire. That's an indication of how much thinner than thread this wire is.

For the record, my procedure:

1) find a chuck which can tighten onto a small dia (I happen to have one, but if I didn't I might get a "pin vice" from a hobby shop, and chuck that in a drill)

2) Chuck brad in drill. Spin it while painting with polish. Let it dry.

3)Tie a single knot around the brad with 1 end of a 10 foot piece of wire*. Do not tie a square knot. This may kink the wire, leaving it weak. Paint polish on knot. Let it dry.

4) Pull the short end of wire (about 3") straight away from the drill.Spin the long end of wire onto the brad. Hold wire a little bit taught while it is being taken up. Take care not to allow wire to tangle. dab a bit of polish on the coil from time to time. Allow to dry.

*If I had a neat spool of wire I would just let it spool off the spool and onto the brad. But I used a transformer which had come apart a bit messy. It woulda tangled doin it that way.

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Toga_DanToga_Dan

Reply 4 years ago

After cleaning wire ends, soldering to the leads, connecting 1.5 v, I got this coil to lift a 1/4" nut. I think it woulda lifted a bit more.

TinyMag,1:4%22nut1.5v.jpgTinyMag+brads1.5v.jpgtinyMag,bolt1.5v.jpg
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Toga_DanToga_Dan

Reply 4 years ago

How many 1/16 in dia mags can be packed onto the surface of a 2 in hemisphere?

---------------------------

4pi r^2 = area sphere

hemisphere =1/2 sphere

1 inch r hemisphere=~ 6 in^2

16^2 = # of magnets / in^2= 256 mags/ in ^2

1500 mags on surface

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drmab

4 years ago

Damn. I was hoping there might be some sort of material that could do that. :(

Anyone know if there are ready-made tiny electromagnets one could buy for a project like that? I'm thinking 1/16" in diameter and not too long.

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Toga_Dandrmab

Reply 4 years ago

http://www.race-mart.com/Nirous_Express-NOR-15746.html

1/16" hole. approx 3/16" overall dia. $50 each

If I had to wind 50 magnets of 1/8" and 1/2 inch long, I imagine I could do so in an afternoon.

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Kitemandrmab

Reply 4 years ago

Open up some motors. Flat motors, like in CD and hard drives, are often made of a ring of small electromagnets.

Otherwise, you're looking at winding wire round nails or pins.

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Toga_Dan

4 years ago

Winding electromagnets isn't too hard. How many magnetized areas on surface, do you figure? Why the 2 inch limit on sphere dia? May I ask what this whatchahoozit is for? How much strength do you need from each mag? (simple terms.. enough to lift a car? a bike? a bb?)

In regards to howto wind electromag, take a look at my instructable vid: "monkey hunter"

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Qcks

4 years ago

Ehh...
Kinda? It's not helpful to you in the slightest, but diamagnetic and paramagnetic materials technically produce a magnetic field in opposition to, or in sync with, an imposed one. You're still left with being able to induce a magnetic field to begin with, but it is selective and can be turned on and off.

Magnetic effects are refined electrical effects, and electrical effects involve subatomic stuff, making them inherently difficult to predict and deal with.

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Kiteman

4 years ago

If you're wanting to magnetise and demagnetise with no moving parts, then I'm afraid that electromagnets are your only option.