1. Motor & Gears: The motor is typically about a 1/2-hp, 6-amp machine hooked to a 120-volt outlet—that's all it takes to overcome the inertia of a stopped door. The machine also slows a door in transit, preventing it from crashing to the garage floor.
2. Drive Guide: This track (aka the T-rail) guides and shields the chain, screw or belt as it moves the door open and closed. It connects the operator to the trolley, which in turn is connected to the door.
3. Height Adjustment: Operator settings determine the distance the door travels. The machine kicks in to arrest the door's motion or to make adjustments if a door isn't opening or closing completely. The force of the door's motion can also be adjusted so the door stops moving if grabbed.
4. Inverter & Battery: To allow smaller, more efficient motors, most garage-door operators use DC current. An inverter switches household AC power to DC, which is also used to charge a battery backup system that kicks in when the power is out.