Controversial Idea...

(anyway isn't the problem that you need a constant speed of rotation to generate a constant current? which i suppose can be fixed mechanically with springs and such)

(little known fact: new york subway cars use special mechanical brakes that generate power back into the grid! this is possible coz the grid for the subway is direct current.)

Special electrical brakes, you mean - basically, when the train wants to slow down its motors switch to being generators. If the current is sent back into the supply it's called regenerative braking; if it's absorbed by resistor banks on the train it's called rheostatic braking.

This was used in the UK, on the DC-electrified line from Manchester to Sheffield which closed in the 1970s. It was so effective that often the amount of power supplied into the system by braking trains exceeded that being used by accelerating trains.

Since the 1990s, it's been possible to build AC-powered trains which use regenerative braking, using hefty electronics and variable-frequency three-phase motors.

(i almost typed "blowing together," soz suzy)

Well, if it's pretty small, the power involved in creating, producing, installing, running and maintaining such devices may outweigh the power generated by them.

Probably would generate more electricity.

The Second Law of Thermodynamics doesn't allow it. The Kelvin-Planck version of the law is "It is impossible to construct a device that will operate in a cycle and produce no effect other than the raising of a weight and the exchange of heat."
Basically thats saying is there is no way to take a given amount of heat from a high[er] temperature body and convert it into an equal amount of work.
Factors that often make a process irreversible are friction, unrestrained expansion, heat transfer through a finite temperature difference, dispersion, hysteresis and i^2R loss in electrical currents.

Homer: Lisa, in this house we obey the laws of thermodynamics!

Same problem. Think of all the energy (stored in food) expended in the feeding the hamsters...wait a minute. Are these really large wheels for hamsters, or wheels for giant mutant hamsters?

I don't know about naked mole rats.

Both ways of stating that are negative statements which are impossible to fully prove. Now looking back at notes, Im mistaken, the second law is experimental, not mathematical. oops.

Give me a few seconds.

No, I'd say its a lazy answer but not misleading.

Couldn't we just change the law to allow perpetual motion?

We could infact change the laws of thermodynamics but then they would be considered wrong.
The question is why can't we construct a machine that makes more energy then it uses. The basic answer would be to point at the laws of thermodynamics and say because they say so. Slightly more complex would be to describe why the system can't work using a diagram with Qh and Ql and W everywhere. More fun would be to use the law of increase in entropy and tie that back into the question. But I don't have the time or the will power to write a book chapter.

Down by Kim's leg is Rufus the naked mole rat who lives in Ron Stoppable's pants.

"What do these scientists want us teaching our children? That the universe will continue to expand until it reaches eventual heat death?" asked Christian Coalition president Ralph Reed, speaking at a rally protesting a recent Kansas Board Of Education decision upholding the law. "That's hardly an optimistic view of a world the Lord created for mankind. The American people are sending a strong message here: We don't like the implications of this law, and we will not rest until it has been reversed in the courts."