How garage door opener/motor works

Thread Starter

jaydnul

Joined Apr 2, 2015
161
How does the motor keep the garage door closed? Couldnt you theoretically lift the garage door from the outside and just spin the electric motor in reverse? Does it take too much force to do that? And if the power goes out how does the motor keep downwards force on the door?
 

WBahn

Joined Mar 31, 2012
27,886
It depends on the kind of drive that is used -- there are a few different kinds. In a leadscrew arrangement, pushing the shuttle (that is attached to the garage door via a linkage of some kind) can't turn the lead screw. Think of the kind of height adjustment you find on the bottom of, say, couch legs in which you turn a nut to screw a post in or out of the leg to adjust the height. What you are asking would equate to sitting on the couch and having the adjustment screw go spinning up into the leg.

For other drives, the internal mechanism of the motor usually involves a worm gear arrangement, which has this same characteristic.
 

MisterBill2

Joined Jan 23, 2018
13,790
There is more to keeping the door closed than just the motor friction. At least for the average residential one or two position vertical door opener with the drive above the door. The opener mechanism has a link to a point about 20 inches down from the top edge of the door, and the track end is almost above the door end of the link. So at that point the door closing has a very large mechanical advantage holding the door closed. The same scheme is used for both the lead-screw type openers and the roller chain openers. The TS needs to take a look at an installed opener if they are not able to visualize my description.
With the larger door openers that simply roll a door up above the opening, in many systems there is an electrically released friction brake that engages whenever the motor is not running.
 

MisterBill2

Joined Jan 23, 2018
13,790
The last three garage door openers thatI have installed as replacements all used roller chain and a cable rather than a leadscrew for the drive. No messy grease to deal with and also lighter to ship. Probably they cost less to ship and to build, as well.
 

WBahn

Joined Mar 31, 2012
27,886
The last three garage door openers thatI have installed as replacements all used roller chain and a cable rather than a leadscrew for the drive. No messy grease to deal with and also lighter to ship. Probably they cost less to ship and to build, as well.
But what about the motor itself? Nearly all of the ones that I've seen have a worm-gear output. This is almost required given the difference in what you want for motor speed versus what you need in the shuttle speed.
 

WBahn

Joined Mar 31, 2012
27,886
There is more to keeping the door closed than just the motor friction. At least for the average residential one or two position vertical door opener with the drive above the door. The opener mechanism has a link to a point about 20 inches down from the top edge of the door, and the track end is almost above the door end of the link. So at that point the door closing has a very large mechanical advantage holding the door closed. The same scheme is used for both the lead-screw type openers and the roller chain openers. The TS needs to take a look at an installed opener if they are not able to visualize my description.
With the larger door openers that simply roll a door up above the opening, in many systems there is an electrically released friction brake that engages whenever the motor is not running.
Yet disconnect the shuttle from the chain or lead screw and the door opens quite easily. The same would be true if the motor could be easily overhauled manually.
 

MaxHeadRoom

Joined Jul 18, 2013
26,285
The last three garage door openers thatI have installed as replacements all used roller chain and a cable rather than a leadscrew for the drive. No messy grease to deal with and also lighter to ship. Probably they cost less to ship and to build, as well.
Both types I am familiar with also have the Worm and pinion at the motor, one item to keep greased as they are generally a plastic substance material.
Amazon have the replacement gear kits.
 

MisterBill2

Joined Jan 23, 2018
13,790
For either drive scheme, it is the linkage between the opener and the door that prevents the door from being opened by lifting from the outside. Even with that latch to the drive released the door can't be opened from the outside if is fully closed. At least not if it is set up per the instructions with the door.
 

WBahn

Joined Mar 31, 2012
27,886
For either drive scheme, it is the linkage between the opener and the door that prevents the door from being opened by lifting from the outside. Even with that latch to the drive released the door can't be opened from the outside if is fully closed. At least not if it is set up per the instructions with the door.
The whole purpose of the latch release on the shuttle is so that the door CAN be lifted (inside or outside doesn't matter) in the event of a failure.

I just looked at the installation instructions for my doors and there is nothing in there about setting things up so that the linkage prevents opening from the outside. In fact, on one-piece doors the position of the linkage could not prevent this and the linkage installation position is dictated by the position of the door in the opened position to prevent back slant.

If the door couldn't be raised with the trolley latch released, then the instructions would need to make it clear how you open the door after releasing the latch. All it says is that after releasing the trolley, that the door can be opened and closed manually as often as desired.

I went out and checked all four of our doors (two at the current house and two at the house we are trying to sell), all of which were professionally installed, and after releasing the trolley, opening the door from the outside was no problem.
 

MisterBill2

Joined Jan 23, 2018
13,790
Only after that latch is released. And the systems that PROVIDE SUCH A RELEASE ARE INDEED DIFFERENT. In most cases pulling the latch release moves the trolley(slider) away from the door a bit. Some linkages even include a spring to make that happen.
AND, my experience has been that just because somebody is employed to complete a task does not assure that it is done right.

But in no case will attempting to raise the door back-drive the motor mechanism enough to allow the door to open.
 

MrChips

Joined Oct 2, 2009
27,686
With a chain or belt driven garage door mechanism, the motor itself uses a worm and pinion gear. You cannot push against this.
I have a Genie screw drive opener. Again you cannot push against this.
 

WBahn

Joined Mar 31, 2012
27,886
But you stated that, "Even with that latch to the drive released the door can't be opened from the outside if is fully closed." In all four of my doors, pulling the release lever attempts to move the trolley toward the door. There is no discernable motion of the trolley when it is released and, even if there were, after opening and closing the door, the trolley is going to be in a position dictated by the door and the linkage.

No one has said that attempting to raise the door will back-drive the motor mechanism. Quite the opposite, we have stated that it is the inability to back-drive the motor is what prevents the door from being opened manually when it is connected.
 
Top