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Magnetic levitation

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Dr. 2N3055

Sun Jul 06 2008, 10:14AM

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Joined: Mon Aug 13 2007, 06:07AM
Location: Finland
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Bringing the old but interesting topic up. I have a question: could hall switches (nonlinear; just on and off) used instead of linear hall effect sensors? Or do the sensors absolutely have to be linear?

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cjk2

Sun Jul 06 2008, 11:53AM

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Location: Nashville, TN
Posts: 158

Using switches rather than sensors would probably lead to the object vibrating. Linear feedback is really needed for stable levitation.

Dr. 2N3055

Mon Jul 07 2008, 03:17AM

Registered Member #952
Joined: Mon Aug 13 2007, 06:07AM
Location: Finland
Posts: 353

Okay then. I'll just have to use infrared phototransistors.

Hall sensors would've been so cool.
I'd want to get rid of the need for a dual power supply for the op-amps. Maybe a noobish question, but how could this be done?

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Conundrum

Tue Jul 08 2008, 01:17PM

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Joined: Thu Feb 09 2006, 11:37AM
Location: "Somewhere in Guernsey"
Posts: 985

You can get linear sensors from old broken 5 1/4" floppy drives. Other sources include old style Panasonic VCRs (three are used in the capstan motor) as well as some hard drives.
There is a modern equivalent which is SMD, however its inferior in sensitivity and directionality to the 4 pin SIL equivalent.

It may also be possible to modify the read head on a hard drive (this consists of a very small nanowire) with a constant current as a magnetic sensor, though this is very finicky and hard to do.

Regards, -A

Smiley faces on the sun... ???!!!!

MagLev

Wed Oct 29 2008, 10:05AM

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Joined: Thu May 29 2008, 08:16PM
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Tesladownunder wrote ...

Reaching wrote ...

.. does anyone know if its possible to levitate a copper or aluminium disc stable via eddy currents(induction)?

It is possible to levitate a dish shaped copper or Al disc vertically but the power is large and the dish may be close to melting. I've not been able to manage it but 50Hz is rather low to work well.

You can in fact pick up non-magnetic washers with an AC electromagnet with an additional copper washer added to the core. Now a levitator for aluminium objects would be really cool

Peter

Actually, there are several types of levitators for aluminum (and, presumably, copper) objects. The book Propulsion Without Wheels by E.R. Laithwaite is an excellent source for these levitators. Unfortunately, the book is rare, expensive, and out-of-print. I had to get it through inter-library loan. The book is mainly about induction motors, but has a whole chapter just on magnetic levitation, with plenty of how-to diagrams and theory. It's a great resource.

Keep in mind, though, that any sort of induction levitator for copper, aluminum, or other diamagnetic materials will cause the materials to become hot if they are pushed deeper into the magnetic field than is necessary for them to levitate (i.e. an aluminum bowl which floats at 12 inches and stays cool will become very hot if pushed 6 inches into the magnetic field with a nonconducting object such as a wooden rod).

Here's a link to another aluminum levitator that works on the same principle. http://aether.lbl.gov/www/classes/p10/levitator.gif

cjk2

Wed Oct 29 2008, 03:44PM

Registered Member #51
Joined: Wed Feb 08 2006, 10:17PM
Location: Nashville, TN
Posts: 158

"Maglev", your link is broken. Now that this topic is active again, ill go ahead and post my most recent work. This is repulsive levitation.

101111

Wed Oct 29 2008, 04:41PM

Registered Member #575
Joined: Sat Mar 10 2007, 10:00PM
Location: Norway
Posts: 199

cjk2 wrote ...

"Maglev", your link is broken. Now that this topic is active again, ill go ahead and post my most recent work. This is repulsive levitation.

Wow, That is impressive! Please, make a project thread out of it so we can see more ;)

cjk2

Wed Oct 29 2008, 10:11PM

Registered Member #51
Joined: Wed Feb 08 2006, 10:17PM
Location: Nashville, TN
Posts: 158

I will actually be updating rfhv.com soon to reflect my 5th version design. In the mean time, enjoy a picture of my controller board.

MagLev

Sun Jan 11 2009, 07:10PM

Registered Member #1512
Joined: Thu May 29 2008, 08:16PM
Location:
Posts: 4

All righty, let's try to fix that link...

http://aether.lbl.gov/www/classes/p10/levitator.gif

Hopefully that'll do it. The device pictured here is very similar to a description of a levitator found in Harry F. Meiners' Physics Demonstration Experiments (more info can be found at Rick Hoadley's excellent magnet site- see link below.

http://www.coolmagnetman.com/magpie.htm

As he notes, a levitator like this is quite expensive and labor-intensive. However, they are quite fascinating to see in action. Here's a picture of one (with a funny comment about cooking pancakes).

http://blog.modernmechanix.com/mags/qf/c/PopularScience/11-1939/med_floating_bowl.jpg

Now to build/fix my own levitators when the parts arrive in a few days...

EDIT: Links still aren't working. Just copy and paste into your browser.

aonomus

Mon Jan 12 2009, 08:04AM

Registered Member #1497
Joined: Thu May 22 2008, 12:24AM
Location: Toronto, Ontario, Canada
Posts: 771

@ MagLev: Your links are incorrectly formatted (valid url, but you borked the bbcode)

As for the levitators, could a 'quick, dirty and cheap' version be made using MOT's perhaps with the top "I" sections ground off exposing the E section?

My blog:

- mostly about electronics and other stuff, mostly to waste time.

MagLev

Mon Jan 12 2009, 06:22PM

Registered Member #1512
Joined: Thu May 29 2008, 08:16PM
Location:
Posts: 4

I've never seen a microwave oven transformer, so I am uncertain. However, I do know one thing: an essential component of eddy current levitators (which is what an aluminum or copper levitator is) is the requirement that there be (at least) two currents, and that the two currents be out of phase with each other. For instance, one type of levitator described in Propulsion Without Wheels involves levitating an aluminum sphere. To achieve this, the author recommends two methods. In the first, one coil is placed inside another, and the two are separated by some sort of iron ring or pipe (to concentrate the field). These two coils are then powered by different legs of a 3-phase supply, giving you two coils that are 120 degrees out of phase.

A variation on this (also described in the book) is where you have the same setup, with the difference being that the inner coil is replaced with a piece of very thick, solid (i.e. not split) copper pipe. In this case, current is induced in the copper pipe by virtue of the magnetic field generated by the first coil. So you still have some sort of phase difference between the outer coil (powered by AC) and the inner "coi", a.k.a. the pipe, which is "powered" by eddy currents.

Either one of these setups is used to levitate a small aluminum sphere.

A variation on this involves levitating a piece of aluminum shaped something like a dish or pie pan. This is described in Meiners' Physics Demonstration Experiments book. However, this one requires 3-phase power.

So I don't know about the MOTs- all I know is that there would need to be some sort of phase difference between different windings. Also, from my research, the shape and size of the object to be levitated is fairly critical, depending on your setup. That is, the sphere levitator described above will only levitate spheres of a specific size- it will not levitate discs, sheets, toroids, or whatever else. So I don't know what shape an "MOT levitator" would be best suited for, either.

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