I was just cleaning up my desk (a little anyway), and found myself sitting with the guts from a servo.
In essense I had:
A potmeter. If it was turned to one side, a motor would turn to one side, and vise versa. A little turning = a slow motor, hard turn = fast motor.
Now, what if I was not turning this potmeter, but a simple spinning disc, acting like a simple gyroscope was attached to it?
Then if the whole thing was tilting in one direction, a motor.. OR a complete servo (with guts taken out) would turn to one direction.