The motive unit, also known as the motor unit and drive system, was the "engine" of the base unit of the Dalek casing which allowed Daleks to move. (PROSE: Prisoner of the Daleks, Remembrance of the Daleks)
Following the Thal-Dalek battle, the Thals who lived in the Thal City revered engineered the motive unit for their own vehicles. The First Doctor recognised a rail transport that ran through the Dalek City's incubation level as operating on the same basic principles as the motive unit. (AUDIO: Return to Skaro)
While Ace was in Spacefleet fighting in the Second Dalek War, she drilled through the motive units of a Special Weapons Dalek, preventing it from moving as she attempted to steal its energy banks. While she did this, it begged her to kill it. Ace listened to its cry until its power ran out. (PROSE: Lucifer Rising)
During the Planetary Relocation Incident, Donna Noble overrode the motive units of the New Dalek Empire, causing them all to spin in place. (TV: Journey's End)