Magnetic Aluminium?

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Came across this and it tickled me.

PBO Feb issue (the one with the flappy cover) page 46.

Gear review - Joby Gorillatorch. A torch on three flexible legs with magnetic feet.

Quote: " Apart from owners of steel or aluminium hulled boats, only those poking around in the engine bay would be able to find enough metallic surface area to ever mount the feet."

Is magnetic aluminium a standard boat building material? Or does this torch have some clever electromagnets that can induce sufficient eddie currents to make it stick?

Stuart
 
Aluminium is paramagnetic (as are uranium and platinum, to mention but two other common boat building materials) what's the problem :D
 
DownWest said:
So what about linear engines? Don't they use ally between magnets to push trains etc. around?
A
Click to expand...

No, they use aluminium (or any other electrically conductive metal) between electromagnets. It's all down to eddy currents in the conductor generating a magnetic field. They had a demonstration in Birmingham Science Museum when I was a kid (that's a long time ago) - a disc of aluminium between the poles of an electromagnet. Press the button to energise the magnet and the disc started rotating - magic!
 
andygc said:
No, they use aluminium (or any other electrically conductive metal) between electromagnets. It's all down to eddy currents in the conductor generating a magnetic field. They had a demonstration in Birmingham Science Museum when I was a kid (that's a long time ago) - a disc of aluminium between the poles of an electromagnet. Press the button to energise the magnet and the disc started rotating - magic!
Click to expand...

What happens, if you're interested, is that as the disc (or plate in the case of a linear motor) moves through the magnetic flux, a voltage pattern is induced in it. This in turn cause eddy currents and these in turn cause more magnetic flux. The induced flux pattern is (more-or-less) what you'd get from a mirror image magnet on the other side from the real magnet. Since it's a mirror image, like poles are closer and repel - hence levitation.
 
nedmin said:
As in eddy current motors that are used in electricity meters.
Click to expand...

Yup. They are particularly clever because the eddy currents are induced by a voltage coil and push against a current coil (may be the other way round, it's late) so the overall effect is that they measure amps x volts, which is watts. That's why the electricity companies get upset if you attach reactive loads to them - they misread, and can even be spun backwards.
 
ccscott49 said:
No, no no, that was clear titanium alloy!!
Click to expand...

Surely transparent aloominum...

[faced with a 20th century computer]
Scotty: Computer. Computer?
[Bones hands him a mouse and he speaks into it]
Scotty: Hello, computer.
Dr. Nichols: Just use the keyboard.
Scotty: Keyboard. How quaint.

Star Trek 4 Voyage Home for non fans!
 
Ubergeekian said:
Yup. They are particularly clever because the eddy currents are induced by a voltage coil and push against a current coil (may be the other way round, it's late) so the overall effect is that they measure amps x volts, which is watts. That's why the electricity companies get upset if you attach reactive loads to them - they misread, and can even be spun backwards.
Click to expand...

And I think that old-style [i.e. mechanical] speedometers and rev. counters worked by eddy currents.
 
Ubergeekian said:
What happens, if you're interested, is that as the disc (or plate in the case of a linear motor) moves through the magnetic flux, a voltage pattern is induced in it. This in turn cause eddy currents and these in turn cause more magnetic flux. The induced flux pattern is (more-or-less) what you'd get from a mirror image magnet on the other side from the real magnet. Since it's a mirror image, like poles are closer and repel - hence levitation.
Click to expand...


A friend of my father who worked for the British Aluminium company - Kinlochleven / Fort William told us of a trick played upon visitors.
The refining of Aluminium required huge quantities of electricity, rectified to DC- quite low voltage but absolutely MASSIVE currents.
The busbars in the floor of the plant were equally huge - to prevent any heat generation.
The vistors would be required to wear safety boots in the plant .Steel toecaps...
I gather the look on their face as they tripped over the invisible magnetic field (busbar in floor) was priceless.
Eddy currents have their uses !

Graeme
 
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