The Grukkers were a type of machine used on Mechanistria. Grukkers were mainly spherical and made of black metal. They had wheels, legs and tentacles, all of which were used for movement. They were controlled by the brains of Mechanistrians, but did not house the brains.
When the First Doctor first came to Mechanistria, he was nearly run over by a Grukker. When he later tried to escape, a force of machines including a Grukker tried to stop him. (PROSE: Peril in Mechanistria)