The motive unit, also known as the motor unit, was the "engine" of the base unit of the Dalek motor casing which allowed Daleks to move. (PROSE: Prisoner of the Daleks, Remembrance of the Daleks)
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)