Garage Door Maven

[Steve from Socal]

Garage Door guru

Anyone a garage door pro, I have a unique door counterbalance that I would like to go over. It is NOT an overhead door it is a ramp on the back of a trailer. It is heavy 500lbs and it has 105 degrees of travel. Due to physical constraints it also has cable pulleys to redirect the torsion shaft assembly below the door.

To clarify the above, the door is 10' high, 8' wide and the pivot location is 114". The door frame has pulleys at 120" that route the cables down the door frame, the shaft is under the floor below the door frame.

I talked to a few door companies that kinda sorta understand the issue, none have suggested using high lift drums however, the door from full open 105 degrees to about 70 is much closer to what a high lift door would be than a regular drum on a regular door track.

Steve

 

[BillK]

Not a garage door pro but just curious what exactly are you asking for ? Do you want to put an opener on it ?

 

[bugnut]

I am wondering if you are needing lift assistance like a gorilla lift, pictures please.
Thanks

 

[kbs2244]

Ditto to BillK

Now that we know what you have,
what is it you want?

 

[Steve from Socal]

I guess none of you guys know what I am talking about because, the crux of it is do I use standard lift cable drums or high lift cable drums.

To humor the gallery it is a ramp door on the back of a trailer. The area above the door just inside the trailer is pretty tight to get a torsion shaft into, the pulleys would just reposition where the shaft is mounted. Some sectional doors have this same set up.

The other thing is, it would be easier to incorporate a motor drive to a remote shaft.

Steve

 

[Hot Rod Grampa]

As I understand it, the issue is balance. A normal system on a sectional door allows for less weight as the door goes up, but it is a measured and predictable change as each section becomes flat and no longer weighs anything. With a ramp door the change is more drastic and is a compromise at best. The bigger trailers use winches and eliminate the springs. As many trailers that I have worked on, including my own, none ever balanced perfectly. You settle for a little lift at the bottom and hold it back at the top.

 

[Steve from Socal]

As I understand it, the issue is balance. A normal system on a sectional door allows for less weight as the door goes up, but it is a measured and predictable change as each section becomes flat and no longer weighs anything. With a ramp door the change is more drastic and is a compromise at best. The bigger trailers use winches and eliminate the springs. As many trailers that I have worked on, including my own, none ever balanced perfectly. You settle for a little lift at the bottom and hold it back at the top.

I agree on the compromise, the real issue is to lift the door from the ground to about the 45 requires a good deal of force. That MAY translate into the door slamming shut from there and, requiring a good deal of force to pull it down.

The high lift drums have a greater moment arm for the first 2 or 3 revolutions of the drum. They lift the entire weight of the door vertically, not unlike the ramp in the first 1/3 to 1/2 of lift. The springs do relax as the unwind into the closed position but, they do need some tension to keep the cables spooled. I already have some kicker springs in the door frame parts list.

Steve

 

[Ironcrow]

I would abandon the idea of torsion springs with winding drums. You need a steep rising rate spring force and the winding drums are just not going to deliver. Instead, I'd put another set of pulleys where you have the torsion shaft to direct the cables back under the trailer floor. From there use linear tension type garage door springs. Two or three springs per side with a slotted linkage to pick up first one, two, then all three springs. This will give a rapid rise in rate to support the ramp as it comes down.

 

[Steve from Socal]

There is just about 16' of movement on the cables, linear springs alone won't work. The torsion springs should work, on a standard drum it is 12 turns, the springs are rated at 170 or so pounds at the bottom. The lifting force to raise the door from 15 degrees below the horizon to just above is around 200 pounds. There are sectional doors with much greater weight than this door, some are vertical lift.

The question remains, would high lift drums be a better match or are the standard drums and spring rate able to balance the door enough to either open by hand or use an electric motor rated at 65 ft lb's of torque without a lot of gearing. The motor I plan to use is already geared to 40 rpm.

Steve

 

[Ironcrow]

High lift is better. The purpose of the large diameter end of the drum is so the cable force doesn't drop off as much while the high lift door is in the straight up portion of its travel. That is similar to your case where the first 30 degrees of ramp raising is mostly a consistent and high cable force. The problem is the drop-off rate isn't quick enough. A high lift sectional door want to drop off from 170 lbs to, say, 70 pounds when the door is up (the proportion of the raised door that is still on the vertical tracks). For this ramp, the cable force at the ramp-up end of travel drops rapidly to near nothing. So...go with high lift drums, go heavier on the spring, and don't wind it as tight as you would for a regular sectional door.

 

[gnpenning]

Do you have the room for high lift drums? The ones I've worked on use 400-8 or 400-12 drums with no clearance.
You wouldn't be able to put 16' of cable on those drums anyway.

 

[Steve from Socal]

Do you have the room for high lift drums? The ones I've worked on use 400-8 or 400-12 drums with no clearance.
You wouldn't be able to put 16' of cable on those drums anyway.

The high lift drums are 525-54, they can spool 230 inches of usable cable. The standard drums are 525-216, they are about 6" in diameter. The high lift drum is 7.5" in diameter, less than an inch of change in shaft placement.

Steve

 

[Ironcrow]

...the springs are rated at 170 or so pounds at the bottom. The lifting force to raise the door from 15 degrees below the horizon to just above is around 200 pounds.

You'll make it work. Is the 170 lbs the number the garage door guys came up with? Realize garage doors go straight up so 170 lbs is 170 lbs. For this ramp the cable is at an angle. If you measured the weight of the door with a bathroom scale...you'll want to do the geometry to accommodate the angle of the cable. It'll take 280 lbs of cable tension, or similar, to hold the ramp horizontal.

 

[Hot Rod Grampa]

The other option to look at is a full vertical lift drum. There is no flat spot. But they get to be a tad tall. The spring rate goes to very little and may work. I do not have access to the engineering here in Florida but remember there needs to be tension on the cable at all times, so one stiff spring may not be as tuneable as a medium and a soft one. As long as you don't turn the spring backwards, you should be ok.

 

[Ironcrow]

Perhaps room to mount shaft, springs, pulleys at front of trailer near ceiling?

 

[Steve from Socal]

Perhaps room to mount shaft, springs, pulleys at front of trailer near ceiling?

No, I actually have a small winch tied to the cables that is all the way in front. The "garage" part of the trailer is the back 17 feet. I had a plan to run the cables at the roof to the front of the garage and then under the floor. I don't have a lot of room but enough for the shaft at the back.

After all of the pondering and little input from "real" garage door guru's I have a plan to roll my own. I ordered high lift drums D575-120 these have 120" of high monument pulley then up to another 12' of cable on the flat drum. That 120" of high lift should give me a pretty good run. The way it works the shaft will rotate a bit more than 8 times top to bottom. I have been looking at the Inch per pulley turn IPPT and the smaller springs wound at greater than the shaft give me more options like Grampa said.

Steve