Antigravity mechanism

The antigravity mechanism was a component of the elevation unit underneath the base unit of the Dalek motor casing, which allowed Daleks to ascend to hover position (PROSE: Prisoner of the Daleks) through Dalek thrusters. (PROSE: Engines of War)

Human historians believed that that the anti-grav pods were developed by Davros on Necros and then bestowed to his Imperial Daleks, giving them a distinct advantage in their civil war against the Renegade Daleks who were still hampered by uneven terrain. (PROSE: Dalek: The Astounding Untold History of the Greatest Enemies of the Universe)