The gate motor rack (not to be confused with the gate track) runs along the bottom of the gate but forms part of the gate motor – not the gate itself. The rack is welded to the gate and the gate motor uses it to move the gate forward and backward. Racks are used in sliding gate motors, not swing gate motors. The rack is also known as the long gear of the gate motor.
Gate Motor Rack
The pinion is the round gear in the motor.
Gate Motor Pinion
The rack and the pinion work together to open and close the gate. The gate motor drives the movement of the pinion which, in turn, moves the rack. In order to disengage the motor, one needs to turn the pinion so that it no longer functions. One can then open the gate manually.
Gate Motor Rack and Gate Motor Pinion

More about the Gate Motor Rack

The rack can be made of steel or nylon. Nylon racks are quieter than those made of steel; however they break more easily and the “teeth” become worn.┬áThe steel racks last longer and are tougher. Although some rusting may occur, usually it is not enough to warrant replacement of the track. Therefore, we prefer to use steel racks.
In order for the rack and pinion gate motor system to work efficiently, it is important that the ground level is even and as flat as possible.

More about the Gate Motor Pinion

The gate motor drives the rotation of the pinion. The gate motor pinion, the rack and the gate must be properly aligned. The centerline of the rack must run on the centerline of the pinion. The centreline of the gate must be parallel to both the rack and the pinion. The gearbox drives the pinion, turning it to the left or to the right. The gate then opens or closes depending on how the controller functions.