gas strut question...

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gas strut question...

Postby madjack » Tue Mar 01, 2005 8:17 am

...I am planning to use 150# gas struts on my hatch. However, when I check 'em out I find waaay to many choices, how about those who have used them give a part# and source, it would sure help out on the figurin' (and save some frustration)
madjack 8)
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Postby toypusher » Tue Mar 01, 2005 8:31 am

madjack,

Do you have a Pep Boys auto supply in your area? They have gas shocks!

Kerry
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Postby madjack » Tue Mar 01, 2005 8:38 am

toypusher wrote:madjack,

Do you have a Pep Boys auto supply in your area? They have gas shocks!

Kerry


...I have plenty of sources (Austin Hdw/Auto Zone/ect) just not enough info to make an informed choice
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Postby toypusher » Tue Mar 01, 2005 8:50 am

I plan on using them, and recall a thread on here about them, just can't remember what is was called. Anyway, I am planning on using the strongest ones that I can for the galley. Not sure what it will weigh or just how well it will balance when open. I think that the 120 or 130 lbs models should do fine. :roll: :thinking:

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Postby SteveH » Tue Mar 01, 2005 9:01 am

MadJack,

Every installation may be different, so go to this page and pick the one you need. http://www.austinhardware.com/dept.asp? ... VVQF500439

The way I did it was measured the distance from the hinge to where I wanted to mount the shock for the extended length (90 degree angle when hatch is up), and then measured what the compressed length would have to be, and picked one off the chart. I'm using 100 pound ones and they work great.

Don't foget to figure the length of the mounting brackets into the equasion.
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Postby emiller » Tue Mar 01, 2005 12:32 pm

You can check out McMaster-Carr they have a page that tells you how to figure out how to mount and what size and also outback teardrop site has a section how to mount them 8)
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Postby madjack » Wed Mar 02, 2005 7:28 am

...thanks for the info, y'all
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Postby Keith » Sun Mar 06, 2005 12:46 am

Here are the part numbers and cost of the trailer rods we use on our 5' wide Modernistic shape trailers. We purchased the gas props from Camp World. They come with two brackets to mount them with. One straight and one with a bend. The other part number is for a package of two additional mounting brackets.

Gas Prop 20"X80LB #19154 were $16.99 each
Gas Prop brackets #19152 were $1.99 package

It takes some trail and error to get them positioned correctly so they will hold the weight properly. I installed them wrong and had a few extra holes in my hatch to prove it.

You can see from this picture the location we used. The hatch works great with the gas props mounted in this location.

<img src="http://www.saber.net/~sking/images/Dvc00021.jpg">

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Postby BobR » Sun Mar 06, 2005 6:38 am

I got mine from SPD...

http://www.spdhardware.com/gs1.htm
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Postby fornesto » Tue May 24, 2005 5:50 pm

OK,

Here I am trying to figure this one out. Could someone post a picture or some really good info on how they installed them? From my early measurements (Comet), it should be around 30" long. I figure my hatch weighs about 60 lbs, so two 30 lb. struts are the minimum. More likely, I'll use two 50-60 lb. struts. Why are some people using 100 lb struts? Wouldn't you have to hang on the hatch to get it back down? I don't want to punch through my hatch or rip off my hinge....so,

1. What is an appropriate weight rating for a two strut setup?
2. About what length struts are people using?
3. 6mm vs. 8mm vs. 10mm ball?
4. What mounting brackets are used?
5. Ball up or ball down?

Thanks fellas and fillies....
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Postby fornesto » Fri Jun 03, 2005 7:10 pm

I ended up going with two 75 lb struts and it barely lifts my 54" wide hatch. I had to arrange them several times because they get ultimate lift the closer they are to vertical when extended. Because out teardrops have a curved rear, they can be a bit tricky to arrange. There simply is not a whole lot of room for the collapsed hinge because as the hatch closes the upper connection point is drawn very close to the lower connection point. A near vertical arrangement means that you must either use short and powerful lifts or mount the longer lifts lower. Since most lifts have a maximum 18" of stroke, you must find the point on the sidewall that is about 18" below the closed hatch. Add about 18" for the cylinder and you are 36" below the open hatch and 18" below the top of the sidewall. If you have a counter, it will likely be much closer than 18" from the top of the sidewall and thus our problems begin. Next time, I will leave notches in the side of the counter or order 100-125 lb lifts. My lifts are at about 45 degrees when extended.
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Postby asianflava » Fri Jun 03, 2005 7:38 pm

You have to remember that even though your hatch may have a dead weight of 60 lbs, you may need more than that to lift it. It will depend on the distance from the pivot.

The easiest way is to get oversized struts and then mount them. That way you will know that they will be strong enough to lift the hatch regardless of where you had to mount them.

Just my thoughts since I haven't gotten that far yet.
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Postby metoady » Sat Jun 04, 2005 10:11 am

his page shows the struts
http://www.outbackteardrop.com/body6.html?

even shows part #s :thumbsup:
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Postby brickz » Tue Jun 07, 2005 11:54 am

Just my .02 worth but mine or two 90# and they work OK but stronger ones wouldn't hurt. Haven't been in strong wind yet. I just guessed based on some other discussion here and got as close as I could at salvage yard. You have way more leverage out at the end of the hatch than the shock does. I actually took a bathroom scale and propped the hatch on it where they would attach to check the force implied. It seems to take a lot more than your intuition would lead you to believe. be careful to design galley to leave clearance for the shocks. Had to cut off the ends of upper cabinets to get mine in. Good luck,
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Postby angib » Thu Jun 09, 2005 6:45 pm

Beware: Long, possibly boring, post!

I once designed and analysed the gas springs to lift a big boat hatch and I thought I'd try repeating the same work for a teardrop hatch. Hey, it is nerdy, but when there's some real serious nerding to be done, I'm your man! Here's my layout for the 56" long hatch of the 'Trailer for Two':

Image

A few general points on this:
- It is instinctive to put the thin rods of the gas springs to the top and the big tubes to the bottom, but this is wrong. Check your car's trunk and you'll find them the other way up. This is because the spring is damped as it reaches full extension, but only if it is in a rod down/tube up orientation.
- I put the spring's attachment to the hatch as far away from the hinge as possible, to put the springs effort as near the centre of gravity of the hatch as possible - this reduces how much of the hatch is cantilvered past the springs. This approach puts a bigger load on the sidewalls, but they're big strong things that can take it.
- The gas spring shown here is the SPD-GS-3100 from SPD Hardware - it says it is also available from NAPA Auto Parts stores. This spring is 28" extended and 16.5" compressed, though I've only used 17" to make sure it doesn't bottom out.

And one final point: This arrangement works for this design. The measurements and results will not apply to your design if it's different, though the principles will.

To analyse the hatch and springs, I drew the hatch opened at six intermediate positions, as well as at fully open and fully closed:

Image

The hatch's weight exerts a moment (or torque) around the hinge so I mesured the lever of the hatch's (assumed) centre of gravity. The gas springs exert an opposite moment around the hinge, trying to lift the hatch, so I measured the lever of the gas springs.

Here is a table of the results, based on a 30lb hatch and two 100lb gas springs. That sort of hatch weight allows for two 1/8" ply skins and four internal ribs.

Image

A little explanation:
- Columns 2 and 3 calculate how the hatch weight is 'pushing down'.
- Columns 4 and 5 calculate how the gas springs are pushing up.
- Column 6 calculates the net result - a positive number is the hatch trying to close itself and a negative number is the hatch trying to open up.
- Column 7 calculates the force you need to apply at the handle or edge of the hatch too open or close it.

What these results show is that:
- When closed, the hatch does not want to spring open on its own (which I think is a good idea) - you need to apply a 9lb pull on the handle to start the hatch opening.
- Very quickly, in less than 10 degress of opening, the gas springs take over and try to push the hatch open for you.
- When fully open, you have to apply a 32lb (downward) pull on the hatch to get it to close and you will have to keep pulling it down until it is nearly closed.

So I also tried an alternative with a 40lb hatch and two 50lb gas springs. That's about the weight of the hatch above with a .032" aluminum covering.

Image

Not surprisingly, a heavier hatch with much lighhter gas springs shows a different result:
- It takes a 14lb lift to start the hatch opening and you have to keep on lifting past half way.
- The gas springs will support the hatch in the open position, but it only takes a 5lb pull on the hatch to start it closing and it is likely to drop all the way down.
I think this combination of hatch weight and gas springs is dangerous - it's too small a force to start it closing (a puff of wind might do it, a breeze certainly will) and it's likely to drop all the way.

So what does all this nerdiness teach us? Well, it shows me that this is a fairly difficult thing to analyse and that there no universal answers that can be used by everyone - the number of different variables that can be changed in different designs is very high. One thing is that apparently quite powerful gas springs (2 x 100lb in the first example) do not make it too hard to close the hatch so, if you are in doubt about what to do for your trailer, it would be sensible to go for higher powered gas springs - for example, even if two 150lb gas springs were used in first example, the force to start the hatch closing would still be 'only' 56lb.

I'd be happy to answer anyone's questions but it's taken about 4 hours to do this work, so I'm not volunteering to repeat it for anyone who asks!

Andrew (in training to be a Nerd-in-Chief) :SG
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