This is the 11551st most frequent Russian word.
дрона
"Drone" (unmanned aerial vehicle).
The word 'дрона' is used here as the singular accusative case of the masculine noun 'дрон' (drone), indicating the direct object of the verb 'видел' (saw).
Я видел дрона в небе.
I saw the drone in the sky.
The word 'дронов' is the plural genitive case of 'дрон' (drone), used here to indicate possession (several of).
У нас есть несколько дронов для съёмки.
We have several drones for filming.
The word 'дроном' is the singular instrumentative case of 'дрон' (drone), used here to describe the tool or means by which the action 'управляет' (controls) is performed.