AC electromagnet and aluminium levitation

[ErikL]

Hi all,
I'm new to this forum as a member, but have come across some of the topics here via google in the past.
I'm trying to build an AC electromagnet levitation device, to levitate a small piece of aluminium.
My knowledge in physics is limited to popular science and interest, but I am pretty handy with tools and soldering and such.
My question is this:
I want to build an AC electromagnet with an iron core (which will be powered by a 24 VAC), about 10 inch in diameter (the core), and levitate on top of it a small aluminium disc (about 2 inches in diameter). Can it be done like that? simply building an AC electromagnet like that, then switch it on, then put the aluminium disc and will float? will the aluminium disc be stable on the electromagnet, or will it fly away like in the jumping ring experiment? I've attached a very simple diagram of what I want to build.

Please, I would appreciate your feedback.

Regards,
ErikL

 

[zoki85]

Read about stability here

 

[ErikL]

Read about stability here

Zoki, thanks for your reply. According to the wikipedia article you've linked to, under Stability>Static, it says that:

Conductors can have a relative permeability to alternating magnetic fields of below one, so some configurations using simple AC driven electromagnets are self stable.

.
So, should I gather from this that the device I want to build falls under the definition of "simple AC driven electromagnet" and will levitate the aluminium disc with stability?

Regards,
ErikL.

 

[zoki85]

I don't think so. You'll have problem with stability quite likely.

 

[ErikL]

I don't think so. You'll have problem with stability quite likely.

Ok, can you please explain why? as this is unclear from the wikipedia article you've linked to. And what would I need, to make this stable?

Regards,
ErikL.

 

[zoki85]

Becouse B-field generated isn't perfectly homogenous + finitelly conducting disc shape isn't symmetrical enough so any small disturbance will destabilize levitation. However, you may want trying experiment of levitating Al-ball in an AC field of two electromagnet coils ( see here ) . That can work.
Regards

 

[ErikL]

Becouse B-field generated isn't perfectly homogenous + finitelly conducting disc shape isn't symmetrical enough so any small disturbance will destabilize levitation. However, you may want trying experiment of levitating Al-ball in an AC field of two electromagnet coils ( see here ) . That can work.
Regards

I see. I've actually came across the link you shared in your last reply while researching the subject. However, I've found this video on youtube:


It looks like a reversed form to what I'm suggesting - just that this time, the aluminium is a large base (1/4" thick) and the AC electromagnet (36 VAC, 60Hz) is levitating on the base. It does move around a bit and slide on the aluminium base - but it seems pretty stable. If I will try my original, simple design, is that the kind of instability I should expect, or would the disc simply fly off, as if I was trying to make one permanent magnet levitating on another permanent magnet?

 

[zoki85]

You're expected to have stronger instability in your original setup than in the experiment in the video.

 

[ErikL]

You're expected to have stronger instability in your original setup than in the experiment in the video.

zoki85, first of all thank you very much for taking the time and replying to my questions.
Second, I hope you do realize your replies encourage me to ask more questions :).

Why would there be a difference? Why would the levitating electromagnet on top of an aluminium base be more stable than a levitating aluminium disc on top of an electromagnet?

One would think there ought to be some sort of symmetry so I could arrange for some sort of stability (even similar to the video) with the reversed roles (as shown in the video).

Regards,
ErikL.

 

[zoki85]

Why would there be a difference? Why would the levitating electromagnet on top of an aluminium base be more stable than a levitating aluminium disc on top of an electromagnet?

Why I can ballance a vertical stick on top of my head, but can't ballance my body on top of the stick? It's nothing else but roles reversed:)
If you really want to levitate a disc-like shape in a magnetic field use a gyroscopic effect

 

[berkeman]

Would the OP's initial arrangement be more stable if an iron ring were placed on the top surface of the coil, so that it helped to make the B-field a bit stronger around the outer edge of the iron core, and a little less strong in the middle of the top surface?

 

[zoki85]

I would recommend experimenting first with aluminium ball in initial arrangement, to see what kind of instability develops.

 

[zoki85]

Stable arrangement with 4 electromagnets and big Al disc:

 

[ErikL]

So, zoki85, if I were interested in making an aluminium disc floating using oscillating magnetic field, instead of the gyroscopic stabilization which the levitron employs, I should use more than one electromagnet? do the electromagnets need to be in operated in some sort of phase or opposing currents?

 

[zoki85]

Electromagnets should be identical, and fixed in a symmetrical fashion.
But, it seems that one electromagnet can be enough for the stability IF the plate is big enough!
I've just found this:

This is as close as it gets to your experimental arrangementCheers