Chumbley
Chumblies were the nickname Vicki gave to the Rills' small robot servants, after the "wobbly" sound they made when moving. The Doctor deduced they were blind because they seemed to feel their way around the exterior of the TARDIS. Later, he determined that they did have the ability to detect sound waves and heat. They were also equipped with a weapon that could project flames. They were powered by a form of magnetism, and could be immobilized by ensnaring them in a metal mesh.
One of the tasks the Rills gave them was to deliver messages. They attempted to deliver one to the Drahvins multiple times but were fired at. They resisted gunfire by deactivating and then reactivated when the firing stopped. They were made of circular rings that grew smaller towards the top. The rings could all fold down into each other, to protect the interior of the robot. (DW: Galaxy 4)
Behind the scenes
According to Jeremy Bentham, the Chumblies were designed by Richard Hunt. Like Daleks, they required a performer to operate the machinery from inside. However, their small, three-foot stature meant that those performers all had to be dwarfs. One of them was Angelo Muscat, who would later play the butler in The Prisoner. The action of the Chumbley's telescoping down into a "closed" position when deactivated made the prop too small for any performer. Thus, a "performer-less" prop was constructed for filming the "down" position.
