Self-sustaining DC Motor, using old 5 1/4" Floppy Drive Magnet

[sm0ky2]

yes the white lines are separations. It looks like, from the video in the provided link, that there are 12 sections.
This is probably standard for those drives, so they should all be about the same.

the saw-tooth pattern that is on the outer edge, is probably from a cutting procedure that makes it a round disk.
At least that is my speculation..  But the changes in the field around this rim are very small, detectable by a tiny compass needle,
and the magnetic viewing paper, but otherwise insignificant towards any affect on bulk matter.

The sections themselves are more likely to have an affect. What I do not know is:
    whether these sections are magnetized N<->S in the horizontal plane, or if they are alternating N and S faces.
That is something I never was able to determine when I examined the disk magnet.

[gyulasun]

Hi sm0ky2,

I would like to understand the followings:

You wrote that "The motor would operate 'as if' it still had current running through it" and you also wrote "however, there was the quite noticeable electric 'hum'  that's why I said it was 'as if' the motor was still running."

(I assume on the electric 'hum' you mean the usual noise such a DC motor produces when runs from a battery, right?)

So my question is: did you hear the (similar to normal running) electric 'hum' when you short circuited the motor pins by a piece of wire or you heard the electric 'hum' when the battery was removed and the motor started to spin down (with no shorting wire) for the 70 to 90 second long time?

IT is okay that a DC motor can work as a generator and produces mainly AC voltage difference across the brushes whenever it spins down and this voltage can drive current in the rotor coil if you short circuit the motor pins with a piece of wire (or a low resistance load) what you did do and the motor stopped within a shorter than the 70-90 sec spin down time, obviously due to normal Lenz effect.

You wrote the followings:

I'm not sure if the shield-plate is necessary, or what effect that had on the whole thing, I left it on there out of convenience, it gave a nice hole to mount it with, and the magnets are kind of hard to separate from the shield-plate without breaking them.   

but nothing that resembles the sectional magnet found in the old 5 1/4" floppy drives.
http://hackedgadgets.com/2007/05/10/magnetic-viewing-paper/
this is the magnet, & shielding plate, notice how it is magnetized in sections. I didn't find much on how these are actually made, or pieced together, what have you. but I believe it is this arrangement that has the most to do with the effect.

The sections themselves are more likely to have an affect. What I do not know is: whether these sections are magnetized N<->S in the horizontal plane, or if they are alternating N and S faces.
That is something I never was able to determine when I examined the disk magnet.   

Well, on your first quote, I think the shield plate in the floppy drive is intended to enhance the magnetic field strength of the (magnetic pole segmented) ring magnet facing the coils. This field enhancement happens because the back plate (the shield) is able to close the adjacent segment poles of the ring magnet on the back side so the poles on the front side can become stronger.
This is exactly the same when you try to use both poles of magnet to do a job: recall a door magnet for instance in which a normal rectangular magnet which is magnetized thickness wise is sandwiched between two soft iron plates, so both poles appear on the edges of the plates and when you attach these two plates to a third soft iron piece the total magnet flux is able to close across the third plate and this attraction is much stronger than when you attach the third plate to one of the plates only.

On your 2nd and 3rd quotes above, to make it easier to understand, I made a picture on the pole orientation of magnets used in hard disk drives because they have exactly similar segmented poles on their both sides and they also have a back plate i.e. a shield to enhance the front poles strength (and indeed shield the back part of the magnet from the rest of the HD drive circuits).
You can see two poles on front and two poles on the back of such magnet, this means also that you have normal opposing poles across the thickness of the magnets and also opposing poles on both the front side and on the back side.
And the magnetic segments on your floppy ring magnet have exactly the same pole distribution, say NS, but they alternate all around on both the top side and the rear side of the ring. Obviously, when there is a N pole on top side then there is an S pole right beneath it on the rear side. And the soft iron plate on the back of the ring magnet closes all the neighbouring poles on the back of the ring magnet, thus enhancing the field of the poles on the front side.

For a Neo hard disk magnet the two poles on the front and the two poles on the rear side distribution mean that you could cut such magnet into half to get two separate magnets which would still be magnetized thickness wise but they would not have two poles any more (but only one) on their front or rear sides, here is a how to link to such deed: http://www.fieldlines.com/index.php?topic=139517.0

I attached one of the magnetic viewing paper pictures (from the link you gave in the first post) to show possible poles next to each other on the top side of the ring magnet from the floppy drive.   Sorry for the long rambling...   

Gyula

[sm0ky2]

Hi sm0ky2,

I would like to understand the followings:

You wrote that "The motor would operate 'as if' it still had current running through it" and you also wrote "however, there was the quite noticeable electric 'hum'  that's why I said it was 'as if' the motor was still running."

(I assume on the electric 'hum' you mean the usual noise such a DC motor produces when runs from a battery, right?)

So my question is: did you hear the (similar to normal running) electric 'hum' when you short circuited the motor pins by a piece of wire or you heard the electric 'hum' when the battery was removed and the motor started to spin down (with no shorting wire) for the 70 to 90 second long time?


Gyula

the 'hum' would occur with battery removed, and no shorting, Both terminals were open, and it would continue long enough for me to walk outside and show my neighbor: " hey, look this motor is running itself!!"
of course, he did not know what to think of the phenomena any more than I did, and as I had no practical use for it at the time, it seemed not much more than a novelty trick...

after reading about back-EMF cancelling, and other such ingenuities concerning DC motors, I couldn't help but think this subject was of some importance after all.

   

[mikemongo]

It might be worth trying to short with a diode.

If the magnet is inducing the motor coil, a diode would stop a reversal of current on the motor windings.

[Magluvin]

lol. Wouldnt it be odd if the magnet and shield plate rotating were all that is needed? Just thinking. If someone has that particular mag and the same kind of shield disk, might as well try to eliminate possibilities. Say use a longer shaft between the motor and mag/shield. get the mag/shield goin, then remove the motor from the shaft. Err, something like that.

Mags