Hatch Gas Spring/Strut Calculator

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Re: Hatch Gas Spring/Strut Calculator

Postby danlott » Tue Oct 03, 2017 12:38 am

pmeyers wrote:The dimensions that I am working with are very similar to those of the hatch calculator. 48" hatch, 28 " strut and 12" stroke length. If the attachment point inside the galley is determined by the strut length as a radius from the hinge point then it would seem to be that when attached to the hatch it would not be long enough to even open the hatch. This would be made worse by the fact that the attachment point on the hatch is calculated on 85% of the stroke. My trailer is a Benroy shape and the hatch curves down at the hinge.


Take a look at the picture that is in the first post.

Image


One end of the strut attaches to the side wall of the galley wall at a point from the hatch hinge point that is equal to the overall length of the of the strut. The other end of the strut attaches to the hatch at a point equal to 85% of the strut stroke length.

In your case the strut should be attached to the galley wall 28" from the hinge point of the hatch. The other end of the strut should be attached to the hatch 10.2" from the hinge point. The measurements should be taken in a straight line from the hinge point and not follow the curve of the hatch.

When the hatch is closed the strut will be compressed to length of approximately 17.8 inches. This compression force is what allows the hatch to open and stay open.

The overall clearance height that you will have with your hatch open depends mostly on your hatch design and the height of the hinge point from the ground level. If you desire more or less overall clearance height then you will need to adjust the recommended strut attachment points.

If you use the dimensions provided in the calculator spreadsheet the overall clearance height should be sufficient for most normal height people.

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Re: Hatch Gas Spring/Strut Calculator

Postby Jeepnick » Wed Mar 07, 2018 3:22 pm

I made an account specifically to post here that the calculator worked for me!

My hatch is oversized at 68"L x 57.5"W and I built it with the intention of making it very strong (and therefore heavy at 74 pounds). I was quite worried about attaching the gas springs in the wrong place and putting holes in my siding where I don't want them. After reading a bunch, I finally settled on using Dan's excel sheet to perform the calculations and it couldn't have turned out better! Nothing like installing something the right way the first time. Thank you!

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Re: Hatch Gas Spring/Strut Calculator

Postby danlott » Mon Mar 12, 2018 6:20 am

Jeepnick wrote:I made an account specifically to post here that the calculator worked for me!

My hatch is oversized at 68"L x 57.5"W and I built it with the intention of making it very strong (and therefore heavy at 74 pounds). I was quite worried about attaching the gas springs in the wrong place and putting holes in my siding where I don't want them. After reading a bunch, I finally settled on using Dan's excel sheet to perform the calculations and it couldn't have turned out better! Nothing like installing something the right way the first time. Thank you!

Image

Nick


Very glad to hear the spreadsheet worked for you/ :D

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Re: Hatch Gas Spring/Strut Calculator

Postby tony.latham » Wed Dec 19, 2018 6:13 pm

danlott wrote:I have made a calculator to help determine the proper gas spring length, placement and force required to properly open and support my galley hatch. I searched the internet for formulas and recommendations for the proper placement of gas springs. This is what I came up with to use. I have not actually used it on my own trailer yet, but I figured I would throw it out there and hopefully it will help someone.

If you do use the calculator please post your results on this thread to help determine if it is accurate and useful.

Here is a picture that goes along with the spreadsheet below.

Image

Gas Spring Calculator.xls


Hope it helps.

Dan


Dan:

Check your PMs, please. :thumbsup:

Tony
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Re: Hatch Gas Spring/Strut Calculator

Postby bknowles86 » Mon Apr 29, 2019 12:07 pm

This is great and extremely helpful - thank you. I am in the final stages of design for my build and trying to get as many things figured out as possible before starting construction. I am planning on doing a rear hatch and front roof "hatch" per the attached drawing. I'm doing 1.5" thick insulated walls, so I'd like to ensure that I have wood backing/blocking in the proper locations ahead of time. I've estimated the rear hatch to be approximately 121 lbs TOTAL weight (will include a spare tire mount) and the front at approximately 69 lbs. TOTAL weight. My question is: is there a way to calculate the dead weight from total weight, per the configuration in the sketch? Thanks!
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Re: Hatch Gas Spring/Strut Calculator

Postby tony.latham » Tue Apr 30, 2019 8:53 am

bknowles86 wrote:This is great and extremely helpful - thank you. I am in the final stages of design for my build and trying to get as many things figured out as possible before starting construction. I am planning on doing a rear hatch and front roof "hatch" per the attached drawing. I'm doing 1.5" thick insulated walls, so I'd like to ensure that I have wood backing/blocking in the proper locations ahead of time. I've estimated the rear hatch to be approximately 121 lbs TOTAL weight (will include a spare tire mount) and the front at approximately 69 lbs. TOTAL weight. My question is: is there a way to calculate the dead weight from total weight, per the configuration in the sketch? Thanks!


I'll chime in here since your post is sitting here unanswered ––but to cut to the chase, I think you're just going to have to build it and weigh it.

I like your profile but question the elephant in the room. The spare on the hatch.

Image

Image

I build Fredrick style hatches which are strong, and not overweight but I wouldn't want to hang a spare off of them. If I tried to build a hatch to support a spare, it'd probably be pushing eighty pounds without the spare. The heavier the hatch, the heavier the gas springs or course. Keep in mind, when the hatch is closed, there is a tremendous amount of pressure coming from those springs.

Spare tires are a problem. We carry a spare in our truck bed. With this new build I'm working on, I thought about looking for a donut spare in a wrecking yard with the right bolt pattern and include a lift on the chassis. That thought has come and gone.

I apologize for not being of much help, but I think folks aren't responding because of the elephant. :thinking:

:frightened:

Tony

p.s. And think about moving the door a bit closer to the rear. You want it even with your hips.
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Re: Hatch Gas Spring/Strut Calculator

Postby bknowles86 » Tue Apr 30, 2019 11:00 am

Thanks Tony. I'm sure it's going to require a significant amount of force per strut to lift the spare, so I'm trying to configure the struts in a way that will be most efficient, using Dan's formula, but flipped in this case. (see attached images).
TEARDROP TRAILER-rear hatch-open.jpg
TEARDROP TRAILER-rear hatch-open.jpg (734.43 KiB) Viewed 5642 times
TEARDROP TRAILER-rear hatch-closed.jpg
TEARDROP TRAILER-rear hatch-closed.jpg (697.77 KiB) Viewed 5642 times
My plan is to build the hatch frame out of aluminum tube to give it the strength it needs without making it too heavy. My reasoning for having the door so far forward is to accommodate a twin bunk near the rear (we have a 5-year old daughter) which actually "pops out" of the sides a bit. I've attached an updated image.
Tear Drop Camper-profile.jpg
Tear Drop Camper-profile.jpg (290.11 KiB) Viewed 5642 times
As per the struts, I suppose as long as I have a general idea of the attachment points I can make sure I have backing in place and then as suggested, weigh the hatch once it's built.
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Re: Hatch Gas Spring/Strut Calculator

Postby bknowles86 » Tue Apr 30, 2019 11:03 am

I did find this sizing guide online - although it's in metric, it seems like it would work as long as the conversions are made correctly. Any thoughts?
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Re: Hatch Gas Spring/Strut Calculator

Postby tony.latham » Tue Apr 30, 2019 12:02 pm

I suppose as long as I have a general idea of the attachment points...


Sounds good. I buy my struts at McMaster.com. They have detailed drawings of the struts plus a no-questions-asked return
policy.

:beer:

T
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Re: Hatch Gas Spring/Strut Calculator

Postby bknowles86 » Tue Apr 30, 2019 1:18 pm

tony.latham wrote: Keep in mind, when the hatch is closed, there is a tremendous amount of pressure coming from those springs.


Tony, one more question: regarding your comment above about pressure when the hatch is closed, could you further elaborate? Thanks!
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Re: Hatch Gas Spring/Strut Calculator

Postby tony.latham » Tue Apr 30, 2019 1:36 pm

bknowles86 wrote:
tony.latham wrote: Keep in mind, when the hatch is closed, there is a tremendous amount of pressure coming from those springs.


Tony, one more question: regarding your comment above about pressure when the hatch is closed, could you further elaborate? Thanks!


When you close the hatch and compress two one-hundred-pound gas springs, they are exerting that force while closed. So you've got two hundred pounds pushing against the hatch.

:frightened:

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Re: Hatch Gas Spring/Strut Calculator

Postby bknowles86 » Tue Apr 30, 2019 1:43 pm

Thanks - so does that mean the hatch will come flying open when released? Is there some sort of gradual opening option similar to the way a car hatch opens, where it requires a bit of an assist to get it started? Also, what does that mean for the amount of force required to get it closed from a fully open position?
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Re: Hatch Gas Spring/Strut Calculator

Postby tony.latham » Tue Apr 30, 2019 6:54 pm

bknowles86 wrote:Thanks - so does that mean the hatch will come flying open when released? Is there some sort of gradual opening option similar to the way a car hatch opens, where it requires a bit of an assist to get it started? Also, what does that mean for the amount of force required to get it closed from a fully open position?


If the geometry is right, the spring will nearly fully compress and then start to lengthen and hold the hatch closed. Just don't ask me what that geometry is. :shock:

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Re: Hatch Gas Spring/Strut Calculator

Postby Tom&Shelly » Wed May 22, 2019 10:48 am

tony.latham wrote:
bknowles86 wrote:Thanks - so does that mean the hatch will come flying open when released? Is there some sort of gradual opening option similar to the way a car hatch opens, where it requires a bit of an assist to get it started? Also, what does that mean for the amount of force required to get it closed from a fully open position?


If the geometry is right, the spring will nearly fully compress and then start to lengthen and hold the hatch closed. Just don't ask me what that geometry is. :shock:

Tony


Seems to me, if you draw a straight line between the hinge and the attachment point on the galley wall (or maybe a mental straight line), the correct geometry is that, when the hatch is closed, the attachment point on the hatch should be just below the line. I think. :thinking:

The idea is that the spring is fully compressed when the strut is along the line, so any past and it is slightly less compressed.

But I haven't seen anyone say anything like that on this forum, and it doesn't seem to be something that would happen automatically with a curved hatch (just the opposite). So maybe my thinking is wrong... :thinking: :thinking: :thinking:

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Re: Hatch Gas Spring/Strut Calculator

Postby Tom&Shelly » Wed May 22, 2019 10:56 am

Sure wish I'd paid more attention to this paragraph in Dan Lott's gas calculator directions earlier:

"To allow for proper mounting support, the attachment points should be figured out early in your build using a drawing program or the old pencil and paper method."

I didn't put enough skeleton in the upper galley portion of the skeletonized walls. I can compensate by attaching the struts to the galley counter, but, in that case, it would be better to make the struts' "extended length" longer than the calculator recommends by an inch or two. Does anyone see a problem with that?

An alternative is to use long brackets to hold the pivots, but, besides being unsightly, there is the structural strength issue, currently being discussed on another thread.

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