T-hangar's bi-fold door: Convert to a motorized opening door?

"G.R. Patterson III" wrote in message
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Garage door openers drive a sprocket that operates a circular chain.
Some of the older units had a block on the chain that tripped a
switch when the door was raised. This block could be adjusted to
fine-tune the system. My Genie units do not have this. I assume
(but do not know) that they simply pull the chain for a fixed
distance (most doors are 7' tall).

They have essentially the same system, except that the block has been
replaced by an analog inside the opener. A worm drive moves a block back
and forth, that triggers switches at either end of the range of movement.
One end tells the opener when it's done opening, the other tells it when
it's done closing.

As with the older units, the end result is that the opener simply pulls the
chain for a fixed distance. In the case of the older units, the distance is
set by the block, in the newer units this is adjustable (within a small
range) by a setting that affects the exact position of the ends of the
internal mechanism.

So. Measure the distance you have to pull your chain to open the
hangar door. Work out the ratio between that and 7'. Rig a reduction
gear out of two appropriately sized pulleys and a belt and drive
that from a chain driven by a garage door opener.

Some problems I see with that:

* You will want to ensure that the mechanism inside the opener is up to
the task. The garage door opener I've had open has a nylon worm drive to
turn the main sprocket for the chain. It wears out even under normal garage
use, with a counter-spring to help reduce the forces involved. Even if the
hangar door is counter-weighted somehow, there may be more friction with the
larger door. It may be a lot to ask of little plastic pieces.

* The opener has a motor speed sensor that tells it when the thing is
getting bogged down too much. Because its main purpose is to avoid someone
getting crushed by the door, it's very sensitive. The sensitivity can be
adjusted somewhat, but probably not enough to account for a significant
difference in force required.

* To make matters worse, in combination with the above issues, a
reduction gear that increases the effective travel of the opener is
necessarily going to increase the force that the opener is required to
provide.

* Finally, using a belt and pulley system for the reduction gear may
result in the belt slipping. If it slips only at the very beginning of the
door movement, and it slips exactly the same amount when opening as when
closing, this might be okay. But otherwise, it will throw the system out of
adjustment.

I would say that with a large enough (i.e. expensive enough) garage door
opener, the above issues may not be a problem. But then you may start
finding that you'd have been better off just designing a custom-made opener
mechanism from scratch. Electric motors aren't that expensive, and the rest
is just a sprocket, switches and wiring, and possibly a new chain (depending
on what kind of "chain" is currently used with the manual opening system).

Pete

Peter Duniho wrote:

* You will want to ensure that the mechanism inside the opener is up to
the task. The garage door opener I've had open has a nylon worm drive to
turn the main sprocket for the chain. It wears out even under normal garage
use, with a counter-spring to help reduce the forces involved. Even if the
hangar door is counter-weighted somehow, there may be more friction with the
larger door. It may be a lot to ask of little plastic pieces.

I had assumed from the description that the opening mechanism on the hangar door is
similar to others with which I've dealt. In those, the chain is operated by hand and
requires only negligible force. It drives a gear that operates the actual opening
mechanism. Usually the gearing is such that the chain must be pulled a considerable
distance to raise the door, which is what results in it being so easy to pull around.
The doors with which I am familiar would require less from the GDO than normal garage
doors would require.

As for wearing out, there was a Craftsman unit in the house I used to own when I
bought it in 1988. It was still working well when I sold the house in 2001. The two
Genie units in my existing home were in it when we bought in 2000 and are doing just
fine so far. No telling how old they are. I installed one for a friend back in 1985
and it's still in service. The ones with which I've dealt are pretty bulletproof. You
might want to change brands the next time yours goes.

George Patterson
If you want to know God's opinion of money, just look at the people
he gives it to.

"G.R. Patterson III" wrote in message
...
[...] The ones with which I've dealt are pretty bulletproof. You
might want to change brands the next time yours goes.

The one I had to fix is a Craftsman. I don't know how old it is.

As far as the gearing/load issue goes: a certain amount of work (force over
distance) will be required to raise the door. If the hangar door needs to
be raised more distance than a garage door does, then more work will be
required for the hangar door, all else being equal.

Of course, if the hangar door is carefully counter-balanced and is on
frictionless mounts, then practically no force is required to move it, and
practically no work is required over the entire opening process.

But assuming that past the gear that reduces the force required on the chain
is a door that is similar in nature to a garage door with respect to the end
resultant force required to move it, you don't get something for nothing.
In order to "extend" the range of the garage door opener enough to match the
total range of the hangar door, you'll have to reduce the leverage of the
garage door so much that the force becomes an issue.

Pete