Faradox revisited - NO brushes, V measurement co-rotating with 2-disk magnets and radial coils

[F6FLT]

Interesting approach.
What kind of Voltmeter were you using?
And - with what sensitivity? 
(e.g. 0.1 millivolts, or what?)

A simple RMS multimeter was sufficient, as the voltage was several tens of mV despite the poor quality of my setup (see photo).
This experiment is very easy to reproduce, even with an electric drill. All you need is a motor with a ferromagnetic axle that protrudes sufficiently, facing a magnet, and the two test probes of the voltmeter cord to touch the axle.

[PhysicsProf]

A simple RMS multimeter was sufficient, as the voltage was several tens of mV despite the poor quality of my setup (see photo).
This experiment is very easy to reproduce, even with an electric drill. All you need is a motor with a ferromagnetic axle that protrudes sufficiently, facing a magnet, and the two test probes of the voltmeter cord to touch the axle.

Tens of mV is surprising and encouraging!
Approx what rpm?
what kind of bearing did you use at the end of the ferromagnetic rod, near the magnet?
Was anything grounded?  or free-floating?
Thanks!

[F6FLT]

@PhysicsProf

I don't know the speed of the motor, a 'Meccano' motor for young DIY enthusiasts dating from the 1960s. For a small motor, it is very fast, but even when it slows down, the voltage is easy to read.

The conditions were strictly identical to those of a Faraday disc: same magnets, same order of magnitude of rotation speeds, same voltage generation logic: the N/S reversal of the magnets reverses the voltage, the reversal of the direction of rotation reverses the voltage, this eliminates the possibility of artefacts from ground currents, and in any case, due to the nature of the measurement by the isolated battery-powered multimeter, the measurement was floating. And the same order of magnitude of measured voltages.

[PhysicsProf]

@PhysicsProf

I don't know the speed of the motor, a 'Meccano' motor for young DIY enthusiasts dating from the 1960s. For a small motor, it is very fast, but even when it slows down, the voltage is easy to read.

The conditions were strictly identical to those of a Faraday disc: same magnets, same order of magnitude of rotation speeds, same voltage generation logic: the N/S reversal of the magnets reverses the voltage, the reversal of the direction of rotation reverses the voltage, this eliminates the possibility of artefacts from ground currents, and in any case, due to the nature of the measurement by the isolated battery-powered multimeter, the measurement was floating. And the same order of magnitude of measured voltages.

Thank you.  Your measurement of tens of mV along the axle is fascinating...
Question - was there a ball-bearing (or what) supporting the ferromagnetic axle NEAR the magnets?

[F6FLT]

The end was not free, otherwise it would have vibrated too much. I seem to remember that I spun it inside a wheel like this one (insulated and attached to the support):

[PhysicsProf]

I'd like to attempt a replication of your device/results of voltage along the axle - that is a unique approach I think.  Nice, a bit surprising.

Looking at a detail (below), is the axle electrically connected to the spinning metal disk?
I suppose that would be important.
Is the magnet spinning with the disk, or just the disk spinning?

Also, is there just one ceramic magnet in the shape of an annular ring (like a big washer) - or two magnets?

[F6FLT]

There is no spinning disc. The black disc on my previous photo was attached to the edge of the black wooden support (the plate to which the sliding contacts are screwed). It is hidden behind the magnets and is insulating, made of a type of Bakelite, except for its central brass cylinder in which the end of the axle spun. There is electrical contact between the axle and this cylinder, but it is not as good as the sliding contacts, so I did not use it.
The magnets can rotate or not, it does not matter. It is easier not to make them rotate, which is the case in the photo.
The block of two magnets comes from a magnetron device. A single magnet is sufficient to observe the effect.
The larger the diameter of the magnets, the greater the effect. Large ferrite magnets are better than smaller but more powerful neodymium magnets.
It is very easy to reproduce the effect; absolutely nothing is critical. One important point, however: the sliding contacts must be on the same side of the magnets (otherwise the currents will oppose each other). Good luck if you try it; It's a guaranteed win.

[PhysicsProf]

There is no spinning disc. The black disc on my previous photo was attached to the edge of the black wooden support (the plate to which the sliding contacts are screwed). It is hidden behind the magnets and is insulating, made of a type of Bakelite, except for its central brass cylinder in which the end of the axle spun. There is electrical contact between the axle and this cylinder, but it is not as good as the sliding contacts, so I did not use it.
The magnets can rotate or not, it does not matter. It is easier not to make them rotate, which is the case in the photo.
The block of two magnets comes from a magnetron device. A single magnet is sufficient to observe the effect.
The larger the diameter of the magnets, the greater the effect. Large ferrite magnets are better than smaller but more powerful neodymium magnets.
It is very easy to reproduce the effect; absolutely nothing is critical. One important point, however: the sliding contacts must be on the same side of the magnets (otherwise the currents will oppose each other). Good luck if you try it; It's a guaranteed win.

No spinning disc!  another surprise to me, but hey- the proof is in the pudding (experimental observation).

"except for its central brass cylinder in which the end of the axle spun. There is electrical contact between the axle and this cylinder, but it is not as good as the sliding contacts, so I did not use it."

Let me get this straight - is the end of the spinning long-rod just "sitting" loosely inside the brass cylinder?   such that there is some friction between the spinning rod and the stationary support- cylinder? and maybe the rod is bouncing around in there a bit?  just trying to get this right, as you built it.
(Approximately how much bigger was the cylinder-inside, compared to the spinning rod?)
Thanks again.

[PhysicsProf]

No spinning disc!  another surprise to me, but hey- the proof is in the pudding (experimental observation).

"except for its central brass cylinder in which the end of the axle spun. There is electrical contact between the axle and this cylinder, but it is not as good as the sliding contacts, so I did not use it."

Let me get this straight - is the end of the spinning long-rod just "sitting" loosely inside the brass cylinder?   such that there is some friction between the spinning rod and the stationary support- cylinder? and maybe the rod is bouncing around in there a bit?  just trying to get this right, as you built it.
(Approximately how much bigger was the cylinder-inside, compared to the spinning rod?)
Thanks again.

...  Pondering ...  is the effect due to the rod spinning in the magnetic field? 
OR... perhaps (more) due to some reaction between the ferromagnetic spinning rod and the brass cylinder...? 
The latter would be more prosaic .. and less interesting to me at least.

[F6FLT]

...
Let me get this straight - is the end of the spinning long-rod just "sitting" loosely inside the brass cylinder?   such that there is some friction between the spinning rod and the stationary support- cylinder? and maybe the rod is bouncing around in there a bit?
...

Yes, and you need to lubricate it a little. It's just a matter of mechanics. If the shaft is shorter and can rotate without vibrating with the end in the air, there's no need for this part.
I put it there because I had lengthened the shaft with a ferromagnetic rod. Without this extra rod, I didn't need this disc support, but I had less voltage because the shaft was shorter (and therefore less difference in B field level between the two sliding contacts).

The analysis is simpler in the rotating reference frame. If you are fixed to the axle, it is the sliding contacts that you see rotating in the magnet's field => Lorentz force => current, and since the sliding contact furthest from the magnets produces little current, the one near the magnet imposes the current.
The analysis in the fixed reference frame is more complicated. Smudge has proposed an explanation, but for me it would only explain the appearance of a certain voltage, not its level, which is higher than what the cause would give in this explanation. Rotation is surely the key. We have the key, now we need to find the lock: the explanation.

What matters for duplication is not the photo of my setup, but the technical diagram on the left. It is complete, sufficient, and can be reproduced in many different ways.

[Magluvin]

interesting..  had you tried rods of different metals, like copper, etc.?  also, the motor is mechanically connected to the rod and basically electrically connected? if so, could a plastic insulator/coupler be put there between the motor and the rod just to eliminate any other possible inputs?

mags