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flannelhead

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?

cjk2

Sun Jul 06 2008, 04:53PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263

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

flannelhead

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?

Conundrum

Tue Jul 08 2008, 06:17PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

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

MagLev

Wed Oct 29 2008, 03:05PM

Registered Member #1512 Joined: Fri May 30 2008, 01:16AM
Location:
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

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, 08:44PM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
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.

101111

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 ;)

cjk2

Thu Oct 30 2008, 03:11AM

Registered Member #51 Joined: Thu Feb 09 2006, 04:17AM
Location:
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.

MagLev

Mon Jan 12 2009, 01:10AM

Registered Member #1512 Joined: Fri May 30 2008, 01:16AM
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, 02:04PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

@ 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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