Alt-BEAM Archive
Message #04281
To:
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Sat, 05 Jun 1999 16:47:17 +0000
Subject: [alt-beam] Re: Maglev info: BEAM forcefield....
Wow!
I must confess, I had my doubts when I read your initial "I proved my
physics teacher wrong" statement a couple of days ago, but this circuit
works! What a clever idea!
btw I couldn't open your picture because it was a bit corrupted. You might
want to save it in a different format.
>Here is some information I came up with through the last 4 months of
>experimenting to make a magnetic weapon. A picture of my "hall effect
>device" is attatched.
>
>The device operates like this: when each Hall switch is on, one polarity
>of voltage is applied to the coil, a current appears, and the tip of the
>core becomes a north pole. The Hall switch is oriented so that this
>polarity of magnetic field turns the switch off before the magnetic field
>has a chance to grow very strong. When the switch is off, the direction of
>current reverses, the tip of the core becomes a south pole, and the Hall
>switch turns back on. This reverses the current again, etc. As a result,
>the device acts like a buzzer, the Hall switch turns on and off very
>rapidly, and the magnetic field wiggles north and south a little, but the
>average field is zero. When a magnet pole approaches, the Hall sensor
>starts turning the coil on north longer than south (or vice versa) in
>order to keep the field in the sensor averaging at just about zero. It's a
>feedback system which creates zero magnetic field dynamically.
>
>What good is this? A device that creates zero magnetic field? Very useful,
>actually. Superconductive plates also create zero field inside themselves
>and thereby repel either pole of a permanent magnet. This is how
>superconductive levitation works. Therefore the above coil-assemblies will
>repel a bar magnet regardless of whether it is an N or an S pole. When an
>N pole approaches the hall sensor, the circuit will send a current through
>the coil more in one direction than the other, which makes the coil's pole
>become "N" rather than zero, and it repels the magnet. And the two
>oppositely-pointing magnetic fields cancel to zero right between the
>magnet and the coil, right where the Hall sensor sits. It's a negative
>feedback system based on naturally occuring oscillator and
>Pulse-Width-Modulation. Cool, eh?
Very!
>One serious problem with the device: Tiny movements in the suspended bar
>magnet trigger the compensating magnetic field after a small time delay.
>This will trigger slightly larger movements, which triggers even larger
>movements, and after a few seconds the magnet will be wiggling so
>violently that it will be thrown out of the device. The device has
>slightly negative stability. If you can get the magnet to stop moving
>initially, the oscillations will build up very slowly or not at all.
>
>A simple solution: place a thick copper bar right below the bar magnet.
>The electrical resistance of the bar will offer some mechanical damping to
>changing fields, this will dampen the magnet motion, and the quivering
>will die away. Another solution: Replace each circuit with an ANALOG Hall
>sensor and a DC power amp (needs big heat sinks,) route the analog hall
>sensor signal through the amp and to the coil, and add a bit of
>differentiated hall signal into the signal going to the power amp. This
>will create some programmable damping via analog computation, and will
>cancel out the effects of the loop-delay which causes the oscillation in
>the first place. And if you succeed in all this, you will be an expert in
>linear control theory and dynamic positioning systems!
Have you thought of putting a resistor across, or in series with, the coil?
Ben
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