Convert perpetual magnet motor output to 5 volt DC
Assuming we can completely ignore the laws of physics, especially as regards conservation of energy, then yes it is possible*.

The device you are looking for is called a "Voltage Regulator", and it takes in a variable voltage and outputs a stable, lower, voltage.

They come in two basic flavours:


Linear Regulator.  These are like automatic variable resistors. They constantly adjust how much voltage is dropped across themselves in order to keep the output voltage stable. They are quite inefficient, and tend to get rather hot with higher currents.
Switching Regulator. These chop the incoming voltage up into small chunks by rapidly switching it on and off.  The ratio of on to off gives the output voltage. A feedback loop monitors that output voltage and adjusts the ratio to keep it stable. A low-pass filter then smooths that on-off waveform into a single constant voltage again. These are much more efficient because they don't waste the excess voltage as heat, they just turn it off instead.


Now the electronics are sorted out, why not head over to Physics.SE and discuss perpetual motion and why it doesn't work in the real world. :)

* for certain values of "possible"