To get back to that first post in this thread;
That was clearly an attempt to design a similar setup, in which
the magnet is cuased to move up and down inside the "collector" coil
by alternately pulsing an electromagnet on either side of it.
Seems to me you'd be expending at least an amount of energy equal
to that produced in the "collector coil" every time you make the magnet
move by pulsing the electromagnet. And most likely quite a bit more.
Also, seems to me the magnet will get stuck at one electromagnet
as it contains an iron core and the permanent magnet will still be attracted
to that when the electromagnet is no longer active, unless you actually
push it away with a pulse of opposite polarity in the electromagnet...
... which obviously will take additional energy.
All in all, seems like an inefficient way to make the magnet move,
and even if that was an efficient way, you're using a coil to
move a magnet through a coil, using current to induce a magnetic
field which moves a magnet which induces a current... You'd be
better off using the feed current directly.
Or at least, that's what it looks like to me.

Nevertheless, if we do away with that suggested mains input,
and if we were to use a slightly different electromagnet arrangement,
we might be able to turn it into something cool.

So let's say we use a sort of "crystal radio" receiver to "leech"
energy from radio waves, but instead of simply using its coil as
a filter and using the amplitude modulation to feed the voice signal
to our speaker or headphones, we simply collect those fluctuations
in charge in a capacitor (with rectifier if needed).
We could have these charges accumulate untill they reach a certain
minimum value, then allow the cap to discharge (using a Zener diode
for example), and use these periodic discharges to for example make
the magnet move. (By feeding this pulse directly into the coil around
the magnet, thus making the magnet jump up)
We don't need two electromagnets on either side of the magnet to make
the magnet move. We only need the coil around the magnet.
We also don't need to pull the magnet back down, we've got gravity doing
that for us. So we only need to give the magnet a good "kick" up,
it will drop down by itself.
And yes, although we might be able to use electrical charge collected
by using a "crystal radio" circuit, the efficiency of the magnet+coil
arrangement will still be far below unity, obviously.
But now, what happens when we use a second magnet at the bottom of
our cylindrical setup (I am assuming here that we have wound the coil(s)
around a cylinder with the magnet inside it, and the cylinder standing on one end),
which is in repulsion to the moving magnet?
It is obvious that the moving magnet will hang suspended in repulsion above
this bottom "stator" magnet. It is also clear that the magnetic field of this "stator"
magnet will have the same field orientation as the coil does when it "kicks" the
moving magnet upward. So during this "kick", the "stator" magnet and the coil
align their fields.
As the current pulse fed to the coil stops, the coils field collapses, and the magnet
no longer experiences a "push" up, and starts to drop down to the bottom of the coil.
During the entire drop, it will induce current in the windings of the coil. Proper use of
rectifiers or diodes should allow for collection of all of that.
We might be able to increase the output by using a stack of magnets in repulsion,
but that would require a slightly different setup. For one, we'd need a number of
"collector coils" to make good use of the multiple field line orientations, and this would
result in a "collector coil" array that cannot be used as the "kicker" coil anymore.
So we'd need to create the desired magnetic field pulse in some other way.
Perhaps putting a coil around, under, or above the "stator" coil (or a combination of these)
would allow us to produce a similar "kick" if we pulse that coil...
A second objection would be the increased weight of the moving magnet stack,
which would obviously need more input to actually move up the cylinder.
So the higher output would also mean a higher input, and the stacked opposing
magnets would mean the collector coils and the "kicker" coil(s) cannot be the same.
On the other hand, we may be able to use a second "stator" magnet atop the cylinder,
which should be in attraction to the moving magnet, but with a spacer in between so that
even when the moving magnet is closest to this top "stator" magnet and does "feel"
its attraction, the attraction is not strong enough to actually hold the magnet there against
the pull of gravity, and the magnet will drop down. This might reduce the "kick" power
somewhat.
Ok, perhaps I should have posted this in the "Half-baked Ideas" section??

Well, any reactions, suggestions, or other types of reply are most welcome!!!

Kind regards,
Koen