RE>Garage Door Openers

["Chao, Harvey" <harvey.chao@xxxxxxxx>]

If you are contemplating the chain drive design - check the following:

With the door closed, try and pull it open by hand as if you were trying to
break in.

Last time I check this out, I was able to lift the door some amount and in
so doing, the chain linkage transmitted the movement to the motor and sense
switches.  The Sense switches "said" the door is supposed to be closed, but
it isn't, so the motor turned on to drive the door closed.  Problem is, by
holding on to the door with the motor trying to drive it closed, the sense
switches then said  " door closing - oops, hit an obstruction, enable safety
override and (depending upon design) stop motor in place or reverse and open
door to release/reverse obstruction from being pinned by closing door.

As you can see, that then enables someone access to your garage (and house?)
simply by pulling up on the door.

Personally, I will only use the "screw drive" design because the mechanics
of that design prevents the above scenario, and to force entry, enough force
must be applied to the door to cause mechanical failure of the mechanisms.
Not perfect, but better than the chain drive design.

Harvey

------------------------------