Day of the Dumpster (Pilot version)

Five teenagers, who hang out in an average bowling alley, and occasionally use their karate skills to fend off a gang of mean bullies, are summoned to save the world by an intergalactic being named Zoltar. He gives them the power to become Power Rangers, and to call upon giant dinosauric robots called Droids to combat the forces of space witch Rita Repulsa.