So many "perpetual motion machines" distill down to "overly complicated flywheel".
It is surprising to many that the more load there is on a generator, the more effort it takes to turn. But perhaps to those who never took the "electric machines" class over on the "power engineering" side of the program, this was never spelled out.
It's the same principle that gives rise to inductive impedance in our AC circuits. In a simple conductor, a changing current creates a changing magnetic field, which in turn induces current in the wire, which would be in the opposite direction of the original current if it were strong enough. As it is, the induced current "bucks", or "impedes", the original current.
In a generator, a changing magnetic field (caused by rotation of the generator's rotor) will induce current in any nearby conductor (like the gen's output windings), and that current will wrap around itself a magnetic field of its own; this is of the same polarity as the original field, and so the two fields "buck" each other (like poles repel, etc.). Since magnetic field strength is proportional to current, the more current flows in the output coils (i.e. the heavier the load), the more the rotation will be "fought". Open the output circuit (i.e. no load at all) and the gen becomes very easy to turn.
You can demonstrate this easily with a largish loudspeaker, something most of us are likely to have laying around. Disconnect it and press gently on the center part of the woofer cone (put your fingers around the dust cap; don't push in on the dust cap!). Note that it's fairly easy to move. Now connect a wire across the speaker's terminals. You'll notice it's harder to move.
Many hands-on science museums now have an exhibit where you can try this, hand- or leg-cranking a generator to light up some incandescent bulbs, drive a wattmeter, etc. I recommend it.
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