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

[sm0ky2]

some years ago, while experimenting with rotating magnetic fields, I came across a strange phenomena.
This set-up used a normal, small DC motor (6-12v) coupled to the magnet and shield plate from an old-school 5 1/4" Floppy Drive.

this shows the magnet w/ shield plate and its' properties.
http://hackedgadgets.com/2007/05/10/magnetic-viewing-paper/


This magnet was attached directly to the gear-head of the motor, and when pulsed (1/4sec - 1/2sec) from a 9v battery (no resistance)
the motor would self-sustain operation for 70-90 seconds.
This seemed extremely 'odd' to say the least, and had me playing with it for endless hours... The motor would operate 'as if' it still had current running through it.
Not simply the "flywheel" effect.

This is what I discovered:

When attached to a fly-wheel of similar weight to the magnet-shield combination, the motor would not behave this way. The fly-wheel effect would keep it spinning for just a few seconds, as the motor slowed to a halt. I believe this was due to the induction through the coils from the permanent magnets in the motor housing, causing a back-EMF, fighting the rotation.

When attached to an axially-magnetized magnet (from a microwave oven), it performed similar to the fly-wheel.

When the battery was connected in reverse, while the 'event' was occurring, it took some time, and energy drain to slow the motor, and reverse the direction of rotation.

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my conclusions at the time were that, the magnet, being magnetized in a sectional manner, induced a current-flow through the motor coils, which helped sustain the rotation / operation of the motor.
Lots of giggles and amazement from the device...
Eventually, I put the thing down, because after all, it was not completely self-sustaining, as it did eventually come to a stop. (70-90 secs)
But, recent studies into magnetic theory have led me to begin thinking about this again, so I figured I'd place this in here to share.
This may have some use, or lead to further discoveries.

The floppy drives are becoming more and more rare, as it is an obsolete, and outdated technology...
semi-hard to get ahold of, so I don't have the materials to replicate another one at this time. but I will attempt to gather one.
Other than that, its very simple to assemble this set-up.

below is my (attempt at) drawing of the device. It is just a motor, with the magnet and shield plate attached.
(note: the shaft in the drawing is elongated, the real device had the mount very near the motor housing)

[gyulasun]

Hi sm0ky2,


If I get you correctly, you intermittently switch on the motor with a 9V battery,  by pulsing it for 1/4 to 1/2 second (by your hand I suppose) and you find the motor maintain rotation of the magnet for 70-90 seconds, much longer than with an flywheel which has an equivalent mass to the (floppy) magnet.

The strange thing is that the motor has a closed circuit for the brief 1/4 to 1/2 second time you attach the battery and for the rest of the run down time, 70-90 secs the motor has an open circuit.  At least this is what I think: your normal DC motor has brushes and the rotor coil becomes an open circuit whenever you remove the battery (and the stator of the DC motor has permanent magnets I suppose).

If this is correct, then the rotating magnet you attached to the shaft of the motor could not induce current in the rotor coil but a voltage only, right?  (and the induced voltage could be measured across the connecting pins of the motor) 
And I assume further that you did not connect the battery during the run down time of the 70-90 seconds but let the rotor slow down to zero rpm, right?

Is it possible you connected the battery for the indicated short time while the rotor was still spinning from a previous run and you got the long spin down time in that case only? Or you started the motor with the battery from a stand still and removed the battery after the 1/4 or 1/2 second, and you got the long run down time?

Anyway, a possible explanation for the long run down time could be the presence of the extra magnetic field the floppy magnet provides, participating in the operation of the motor at the very moment of the connection of the battery. 
You surely found already that the rpm of a normal DC motor could be influenced (either positively or negatively) by placing a permanent magnet near to or directly onto the outside of the motor stator body, this is how I mean the effect of the floppy magnet on the operation time in your case. Of course there could be other factors present.

Maybe you could adjust the distance between the floppy magnet and the front part of the motor to see how it may influence the run down time?  Also, if you happen to have a diametrically magnetized ring magnet, you could also test it (making sure for adding some extra weight to it to make for any mass difference between the floppy magnet and that ring magnet.
What is the diameter of the DC motor and that of the floppy magnet, just curious.

Thanks for sharing this puzzle.

Gyula

[conradelektro]

some years ago, while experimenting with rotating magnetic fields, I came across a strange phenomena.
This set-up used a normal, small DC motor (6-12v) coupled to the magnet and shield plate from an old-school 5 1/4" Floppy Drive.
.............................

This reminds me of Harold D. Aspden and his "virtual inertia":

http://de.scribd.com/doc/76567187/1995-Harold-Aspden-Discovery-of-Virtual-Inertia#scribd

--- citation from that page --------------
Imagine an electric machine having no electrical input itself and which, when started on no load by a drive motor and brought up to speed  (3250 rpm), thereafter runs steadily at that  speed  with the  motor  drawing a little extra input  power  with a time  decay  rate of  about  two minutes.  The machine rotor has a  mass  of 800 gm and at that  speed  its inertial kinetic  energy  together with that of the drive  motor  is no more than 15 joules [to overcome friction], contrasting with the  excess  energy of 300 joules needed to satisfy the  anomalous  power  surge [to spin up from rest.] Imagine further that when the motor, after running five minutes or more, is switched off and the machine  is stopped,  you can restart  it in  the same or opposite direction  and find that it  now  has a  memory  in  the  sense  that it will not  now ask  for that 300 joules of excess input, 30 joules will suffice provided  the  time lapse between starting and restarting is no  more than a minute or so.
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I could not find out whether one has to spin a magnet or just mass in order to see that "memory effect".

Greetings, Conrad

[sm0ky2]

If this is correct, then the rotating magnet you attached to the shaft of the motor could not induce current in the rotor coil but a voltage only, right?  (and the induced voltage could be measured across the connecting pins of the motor) 
And I assume further that you did not connect the battery during the run down time of the 70-90 seconds but let the rotor slow down to zero rpm, right?

This was my thoughts as well. there was a detectable voltage occurring at the terminals (A/C?) and shorting the terminals seemed to shorten the time that the motor would continue to operate.
however, there was the quite noticeable electric 'hum'.  That's why I said it was 'as if' the motor was still running.
I couldn't get my meter at the time to show a current, but I think that's because of the way the slip-ring switches back and forth, its not a real rectification. and I did not have an a/c current meter.

the only diametrically magnetized ring I had at the time was too large to produce any testable results, so I didn't go down that road.

Is it possible you connected the battery for the indicated short time while the rotor was still spinning from a previous run and you got the long spin down time in that case only? Or you started the motor with the battery from a stand still and removed the battery after the 1/4 or 1/2 second, and you got the long run down time?

The second case - motor was pulse-started from a standstill, by hand via touching the 9v to the terminals directly.

And yes, I did perform some tests with sticking other magnets to the side of the motor housing, while there were some minor effects, nothing as substantial as the one described here.

motor size - it was relatively small DC motor, about the diameter of a US quarter. maybe 1&1/4" - 1&1/2" long.
rated at 6-12v I think

[pomodoro]

I wonder if the motor is necessary? Spinning by hand and having the shaft vertical hanging by a cotton thread could be a good test. I've got a few of these drives as well as 3.5 inch ones stashed up somewhere. Might give it a go .