Perpetual motion is theoretically impossible. In order to have perpetual motion, you would need over 100 percent efficiency and to overcome drag, gravity and friction.
When faced with someone who claims to have one, it is often quite difficult to see where they have erred. The patent office insists on a working prototype for this reason. The inventors usually have great zeal and can be quite intelligent, but when pressed for details, refuse to divulge them.
The long colorful history of perpetual motion devices can be found online.