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" Door Details  (Illustration by Merce Iglesias) The torsion spring, not the operator (or motor), does the heavy lifting. Aesthetics aside, the big changes in today&amp;#039;s 300-pound steel doors are in insulation. Tighter perimeter seals and sandwiched polyurethane panels get some doors&amp;#039; U-factors, which measure resistance to heat flow and air infiltration, down as low as 0.2. A door under 0.3 qualifies for a 2010 tax credit of up to $1500. Anatomy of an Operator  (Photograph by J Muckle) &amp;amp;gt; 1. Motor &amp;amp;amp; Gears: The motor is typically about a 1/2-hp, 6-amp machine hooked to a 120-volt outlet\u2014that&amp;#039;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&amp;#039;s motion or to make adjustments if a door isn&amp;#039;t opening or closing completely. The force of the door&amp;#039;s motion can also be adjusted so the door stops moving if grabbed.  4. Inverter &amp;amp;amp; 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. The Cul de Sac Hackers In the past, suburban burglars sometimes gained access to garages by using radio scanners to eavesdrop on a code transmission between a remote control and a garage door. Doors in the 1960s were easy targets\u2014they used only one code. In the 1970s and &amp;#039;80s, code grabbers pilfered one of 256 codes that the remotes cycled through. &amp;quot;Since the mid-1990s, we&amp;#039;ve had rolling codes with billions of combinations,&amp;quot; door-operator manufacturer Chamberlain&amp;#039;s Paul Accardo says. &amp;quot;The remote sends a code to the receiver; it opens the door and creates a new code for the next time the door opens. Someone could still capture that code, but it won&amp;#039;t be used again.&amp;quot; Hear that, punks? Drive Mechanisms Belt  Among the quietest (and costliest) drive options, the belt&amp;#039;s Kevlar polymer body is molded into nubby teeth on one side. These rotate through a gear on the operator top to pull the trolley.  Chain  The cheapest and oldest technology, the bike-chain-style chain sits slightly slack when the door is open\u2014at least 1/2 inch above the bottom of the T-rail. The chain makes a racket, but maybe that&amp;#039;s a good thing when your teenagers are sneaking out. Screw  A continuous threaded shaft connects the operator to the trolley, and its arm reaches for the door. Its threads require biannual lubrication with silicone, and it wears out the trolley more quickly than the other options. But the screw is the Goldilocks drive\u2014median price and noise level. "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/home/outdoor-projects/how-to/a6041/garage-door-opener-how-it-works/>