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4hv.org :: Forums :: General Science and Electronics
<< Previous thread | Next thread >>   

Magnetic levitation

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Author Post
Sun Jul 06 2008, 03:14PM
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
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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Sun Jul 06 2008, 04:53PM
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location: Tennessee Tech University, Cookeville, TN, USA
Posts: 263
Using switches rather than sensors would probably lead to the object vibrating. Linear feedback is really needed for stable levitation.
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Mon Jul 07 2008, 08:17AM
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
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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Tue Jul 08 2008, 06:17PM
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: Republic of Guernsey
Posts: 3779
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
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Wed Oct 29 2008, 03:05PM
Registered Member #1512
Joined: Fri May 30 2008, 01:16AM
Posts: 4
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


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
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Wed Oct 29 2008, 08:44PM
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location: Tennessee Tech University, Cookeville, TN, USA
Posts: 263
"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.

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Wed Oct 29 2008, 09:41PM
Registered Member #575
Joined: Sun Mar 11 2007, 04:00AM
Location: Norway
Posts: 263
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 ;)
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Thu Oct 30 2008, 03:11AM
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location: Tennessee Tech University, Cookeville, TN, USA
Posts: 263
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.

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Mon Jan 12 2009, 01:10AM
Registered Member #1512
Joined: Fri May 30 2008, 01:16AM
Posts: 4
All righty, let's try to fix that link...


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.


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).


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.
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Mon Jan 12 2009, 02:04PM
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 800
@ 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?
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Tue Jan 13 2009, 12:22AM
Registered Member #1512
Joined: Fri May 30 2008, 01:16AM
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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Sat Nov 27 2010, 07:53AM
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Posts: 599
Classic Laithwaite maglev video of his 'magnetic river'. Rather cool!

There's also a paper here:

that talks about Laithwaites lev stuff quite a bit.
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Fri Mar 16 2012, 05:45PM
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Posts: 599
FWIW a few months back I built a maglev set up using a combination of permanent magnets for the lift and a spinning aluminium disk giving the electrodynamic levitation for the stability. Air gap was about a centimeter.

I did some measurements of the drag on the aluminium from the magnets and it was only about 50-100 mN, so the overall lift power seems to be about a watt per kilogram, or so, and I could probably get it a lot lower.

Technically it was only pseudo levitation in the actual demo version, because I had to tether it laterally against the electrodynamic drag- my final version works like a train, so it will be pulled along by a propulsion system (probably a linear motor) rather than the tether.
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Sun Jul 22 2012, 09:44PM
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Posts: 599
This is pretty cute, albeit a bit wobbly looking because of the lumpy fields they're generating:

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Wed Oct 09 2013, 02:05AM
Registered Member #26228
Joined: Tue Jun 25 2013, 12:22PM
Posts: 1
I know this is an old thread, but I am trying to build a magnetic levitator and I am a self taught electronics hobbyist (noob). Currently I have a working levitator, but it becomes quite unstable if it is disturbed at all. I am hoping to implement the feed forward circuit in the first post, but I am unfamiliar with OPAMPs. How am I supposed to power it? does it require a negative voltage?

Any comments, suggestions, or ideas would be greatly appreciated!
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Sun Oct 20 2013, 07:42PM
Registered Member #2529
Joined: Thu Dec 10 2009, 02:43AM
Posts: 599
There's plenty of circuits around to do that.

I haven't tried it:

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