The technology herein relates to rotating a second structure, which can be a turret, relative to a first structure, which can be a vehicle. The system can include a motor unit having a motor with a motor gear to rotate a drive shaft and a drive gear. A manual input shaft can also be configured to transmit rotation to the drive shaft. The motor can have a central axis that forms an angle of less than 90 degrees with a plane substantially defined by an outer surface of a gear box coupled to the motor. A mounting bracket is configured to allow mechanical communication between the motor unit and an internal ring gear. The mounting bracket has a mounting frame defining at least a first slide channel. A first motor unit coupler has a slide flange that is slidably received by the mounting frame and receives a motor unit. The internal ring gear can be mounted to a vehicle and a turret can be pivotably disposed within the internal ring gear. A motor unit is mounted on the turret and a drive gear is rotatably mounted on the motor unit and in direct engagement with the internal ring gear.