To make an electric motor generator, attach a power source, such as a small gasoline engine, to the shaft of a permanent magnet electric motor. Determine whether an electric motor is a permanent magnet electric motor by spinning the shaft. If you feel growing resistance the faster you attempt to spin the shaft, then the motor is a permanent magnet electric motor.
Build a platform for the permanent magnet electric motor and the gasoline engine. Place the gasoline engine at one end of the platform such that its shaft can be parallel to the shaft of the electric motor. Drill holes in the platform to bolt the gasoline engine to the platform. Using an Allen wrench or screwdriver, attach one pulley to the gasoline engine shaft and another pulley to the electric motor shaft.
Position the electric motor on the platform so that the pulleys line up, and place a fan belt around the pulleys. Place the electric motor on the platform as far as possible from the gasoline engine to fully stretch the belt. Drill elongated holes in the platform to mount the electric motor, which allows for easier adjustment of the belt's tension. Bolt the electric motor in place.
Separate the wires that supply power to the motor, and power up the gas engine to spin the electric motor's shaft. Be careful not to touch the wires as they are charged with current.