Because he is so disgustingly obese, Robotnik has trouble seeing his feet, walking any further than the front door, and standing for long periods of time. He installed elevators in the lab so he didn't have to climb its many stairs, widened the door frames and reinforced the toilet.

His answer to his lack of mobility is not to go on a crash diet but to build a spaceship, the Egg-O-Matic, which he molded perfectly to his bulbous body, and in which he can zip around the zones and launch attacks on Sonic.

The Egg-O-Matic is fast, it has to be if he is ever to catch up with the supersonic one, and it is armed with a vast array of weapons to be deployed on Sonic when he does catch up with him.