Creating a device that runs for a couple of hours after being "engergized" is
a fine idea, and well within the realm of possibility.

The idea of feeding back "extra" output energy into some sort of generation
scheme is misguided, however.  Thanks to the laws of thermodynamics, you're
much better off tuning your system so that there ISN'T any extra output
energy.  For example, consider a motor/generator scheme.  In order to get
some number of watts out of the generator, you need some factor greater than
1 times that number of watts as mechanical input to the generator, which has
to come from the motor.  That means that the motor needs ANOTHER factor
greater than 1 times that number of watts at its electrical input, in
addition to whatever mechanical show it was preforming.  If, on the other
hand, you use a more efficient motor and tune your mechanics so that your
output motor uses the same amount LESS energy as you might have gotten from
your generator, you don't have those losses.  SAVING power is 100% efficient
(or close to that.)  Regenerating power is MUCH less efficient.  (as a
related real-world example, fluorescent lights are more efficient than
incandescents not because they're brighter, but because the waste less
electricity generating heat.)

I'm inclined to believe that you can learn just as much reducing your power
consumption as you could trying to implement various regeneration schemes.

For instance, do you know what it takes to make a very efficient electric
motor?  Do you know which motors available are most efficient?  Can you
drive a motor with itty bitty pulses so that it will run for a long time on
a particular amount of energy (ie you can pretty easilly design a circuit
that will run for a predicable time providing periodic pulses containing a
fixed amount of energy.  The trick is finding/building a mechanical system
that can make use of those pulses.)  (As an extreme, you can get electric
clock mechanisms that run for years off a single AA battery.  I HEAR that
the motor is quite hackable WRT the frequency of the pulse train, and people
have built robots using these to drive the wheels...)

BillW

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