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Garage door openers
operate through a large motor unit that raises and lowers overhead
doors after the command from a control unit. There are three types of
drive mechanisms: bicycle-type chain and sprocket, plastic strip, and
worm-screw drive. No design has been judged superior and all work well.
The control unit must be key or wireless operated. If key operated, the
driver must leave the car to unlock the door. If wireless operated, the
driver has a mechanism inside the car with a button, set on a frequency
to open the door. Better units offer security codes, overhead lights,
and economical models with a 1/4-hp motor, all models must incorporate
an optical sensor that detects resistance when closing. |
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