Herb Copperbottom runs home to his wife, Lydia Copperbottom, because his baby is being delivered. Herb and Lydia put together their baby, Rodney Copperbottom
Rodney grows up watching Bigweld on TV. Bigweld is an entrepreneur and Rodney is inspired by his motto, “See a need, fill a need”. This begins Rodney’s dreams of being an inventor, just like Bigweld.
Rodney invents a robot called Wonderbot, to assist his father at his job as a dishwasher. The Wonderbot works great and is able to assist Herb in washing dishes, but when the supervisor walks in, the Wonderbot goes crazy and causes a mess. This event leads causes Herb to suggest that Rodney should go to the big city to follow his dreams.
When Rodney arrives in Robot City, he discovers the company of his hero Bigweld is not as friendly and inviting as it seemed to be on TV. He is kicked out by Phineas Ratchet, who is acting as the CEO of Bigweld Industries. Ratchet and his mother, Madam Gasket, have turned the company into a chop shop, that destroy old spare parts and scrap and turns them into new parts to sell for profit.
After being kicked out of Bigweld Industries, Rodney runs into Fander Pinwheel, an eccentric “outmode” robot who is falling apart. Rodney manages to fix Fender’s neck, so Fender takes him in.
Fender introduces Rodney to his family, the “Rusties,” comprised of Piper, Crank, Lugnut, Diesel, and their mother, Aunt Fanny. The community soon finds out about Rodney’s prowess as a mechanic, and he quickly takes up the mantle of repairing those in need. Although he is heralded as a hero temporarily, the severe lack of spare parts means that Rodney cannot keep up with demands.
Rodney and Fender attend the Bigweld Ball in hopes of finding Bigweld. Rodney calls Ratchet out for getting rid of Bigweld and exposes himself as the one who has been fixing the robots.
Fender is captured by a street sweeper and is taken to BigWeld Industries. Theres he discovers that Ratchet and Gasket plan to destroy the “outmode” robots in the city and turn them into new parts.
While fender is at Bigweld industries, Rodney head to Bigweld’s mansion. There, Rodney finds Bigweld constructing an enormous domino chain. Bigweld informs them of Ratchet and Gasket are in control of the company and that there is nothing he can do to help. Rodney resigns himself to return home.
Just before Rodney can head home, Fender and the Rusties show up. Fender explains the atrocities he’s seen at the Chop Shop. Together, they decide that they need to do something about it. Soon enough, Bigweld joins them and the group return to Bigweld Industries.
As the movie climaxes, Rodney and the Rusties confront Gasket. A skirmish ensues, and Gasket and Ratchet are defeated. Bigweld declares that the company will no long pursue monetary gain in the same way they had, and that spare parts will be made available for all.
The crowd erupts in a big musical number, “Get Up Offa That Thing.”