Hatch Gas Spring/Strut Calculator

[Tony Latham]

Hey there! Question about the weight rating for the struts: When I get the weight at 50% hatch length, do I get EACH strut to lift about that weight? Or am I dividing that weight by two, and getting each strut to support HALF the weight? Sorry if this is obvious...

Are you using the Excel calculator?

Tony

 

[Sgt. Paintball]

Just a reminder. The spreadsheet calculator is designed to be utilized when your gas struts are installed in a more vertical position similar to how they are illustrated in the picture. A more horizontal position will require more force and the calculator is not designed for that. Also, the more force required will place increased forces on your hatch, galley, and hinge area, which can lead to failure.

Dan

So does this mean that you could not use the calculator for a square drop? I have a flat hatchback that is a flat 90 degrees vertical square when closed and then opens on a 90-degree angle that is parallel to the ground when in its open position and the gas struts would be attached inside the galley wall and to the inside of the parallel hatch. Can I use this calculator for my build? Let me know if you need pictures to explain?

 

[reyno2ac]

I know this is an old thread...but I had to create an account just to say thanks! This calculator worked perfectly and my hatch not only opens effortlessly, but holds itself closed!

Thank you!!!

 

[Tony Latham]

I just revisited my old Youtube video, Test Driving the Teardrop Camper Hatch. It's the first lid-lift after installing the gas struts.

[youtube]5t_Ujc6oEl0[/youtube]

It's nothing unique, but the music is great!

Tony

 

[mariellec]

I am a bit confused about the strut installation, and not sure which numbers are 'negotiable.' My hatch measures 48" and weighs 50 lb. The distance from the hinge pivot point to the galley attachment point is 24" without hitting the counter or the gusset. I am confused about where to find the 'stroke length' since the struts I am finding only give the extended and compressed lengths and I cannot find anywhere that tells me how to compute the stroke length. It seems like it SHOULD be the difference between the two, but I cannot find information to confirm that. So I am stuck, and not sure why it was so easy for everyone else???

 

[mariellec]

Also, I see some posts with the strut installed with the barrel attached to the galley and some with the barrel attached to the hatch...which way is recommended?

 

[Tony Latham]

...since the struts I am finding only give the extended and compressed lengths and I cannot find anywhere that tells me how to compute the stroke length.

I buy my struts from https://www.mcmaster.com/products/gas-springs/ They've got PDF diagrams of each strut. It'll show the stroke.

As far as the barrel up or down, you want the rod down when the hatch is closed to keep the seals from drying out.

Note the red arrow. If the strut is just below the hinge axle, it won't push up on it when it's closed.

Tony

 

[mariellec]

Thanks, Tony.

 

[DesertApprentice]

The standard drawing shows the structs lean in a forward position when fully extended.

Since my hatch is relatively vertical, following the formula, my struts would lean backward when fully open, see the red line in the illustration.
Do all the calculations still apply?
Thanks a lot!

 

[working on it]

The standard drawing shows the structs lean in a forward position when fully extended.

Since my hatch is relatively vertical, following the formula, my struts would lean backward when fully open, see the red line in the illustration.
Do all the calculations still apply?
Thanks a lot!

* Finally, someone with a vertical (or nearly so) hatch on the forum again; I thought I was the last one to try to use a gas spring on a (home-built) squareback. I started out just lifting the hatch by hand, holding it up with one hand, then inserting prop rods and raising it to a steeper angle overhead. That grew to be a pain over time, so I wanted mechanical help. A linear actuator was my first choice, but wasn't happy with the prices, so I ended up using a gas spring. https://www.tnttt.com/viewtopic.php?f=21&t=61432

* I tried this "Hatch Gas Spring/Strut Calculator", but lost track of the results (due to computer errors), then went off on a tangent, trying other calculators, and ended up using a combination of math and trial & error https://www.tnttt.com/viewtopic.php?f=21&t=69023#p1211649. But, it works, lifting my hatch up to where it floats at 90 degrees (unless the weather's cold, and then it still floats at 45 degrees open), and is real easy to lift the remainder of the way, to my chosen angle (105 or 110 degrees, depending on the ground height, so the hatch is out of the way ...and head-bumping height), using small prop-rod extensions.

* I never tried this calculator after that to see how it would've ended-up, but the initial calculations came up with 125lbs to lift it, but that was for a curved hatch (I presume), since later calcs on another site said 150lbs x 2 gas springs. I ordered two. Once installed, yep 2 x 150lbs springs would've lifted it almost vertically, not to the 90 degree level position I desired (plus, I'm sure that trying to close the hatch overcoming dual 150lb springs would've created another problem, probably with my back or the plywood mounting points deteriorating). As is, a single 150lb spring, mounted nearly in the center of the galley shelf, does what I wanted, and I have the other spring leftover as a spare.


0

 

[Mark Gunter]

I'm trying to use the calculator. My door length is 56" and weight is 60lbs.

Ideal extended strut length, according to calculator, is 33.6"

I find a 30", 100 lb. strut on Amazon. Specs say Extended Length: 30.9", Compressed Length 17.1"

I'm assuming I subtract 17.1 from 30.9 to get the stroke length? If so, that's 13.8"

Bottom line, calculator says I need 33.6" at 90 lb force, and hook it up at 11.73" from hinge ctr pt.

I can get 30.9" at 100 lb force ... should I still be attaching that at 11-3/4" or 12" or so?

 

[Mark Gunter]

Hmmm, looks like I can get a 35" at 100 lbs. Gonna try that in calculator.

 

[Tony Latham]

I buy my gas springs from McMaster. They have a great selection and if they don't work, you can exchange them.

https://www.mcmaster.com/products/gas-springs

I'm assuming I subtract 17.1 from 30.9 to get the stroke length? If so, that's 13.8"

Yep. McMaster has diagrams of all their gas springs in PDF.

Tony

 

[Onajourney]

I used this one and they worked great. They are also very price competitive.

https://www.gasspringsshop.com/gas-spring-calculator/

 

[Mark Gunter]

Thanks Tony & Onajourney!

Man that's a damn fine calculator at gasspringsshop.com, I’m much impressed

 

[Mark Gunter]

Just an update to say that I went with the gasspringsshop website and calculator and my struts are scheduled to arrive today. Thanks for the tip, Ona

 

[JP2023]

Hi Dan, thanks for the strut calculator! You have really helped a lot of builders on this forum, and that is awesome!!

I am in the final stages of my build. All I have left to do are the gas struts (saving the best for last!)

I am little nervous that I will place these wrong, since everything that could go wrong has gone wrong with this trailer. Especially since that rear hatch door is my finest carpentry work yet.

When I install the strut using the measurements in the calculator, I will have to compress the strut about 4" to mount it. Does that sound correct? Do I raise the hatch higher in order to attach the strut when it is fully extended? Is there an easy way to compress the spring to install them?

Overall hatch length is 56.25,
Extended length of spring is 32.25
Stroke is 12.5
Hatch Dead Weight is 58 lbs
Spring LBS each- 67lbs

Here are a couple of pics of my rear galley hatch-

 

[Tony Latham]

I will have to compress the strut about 4" to mount it. Does that sound correct?

No, it doesn't. I think you need shorter struts. I can't imagine what it would take to compress those beasts and get them mounted.

Dan's calculator is great, but I couldn't use the suggested spring length because of the configuration of my countertop and stove location. I just went with shorter springs. Also, my 55-pound hatch needed two 90-pounders.

https://youtu.be/5t_Ujc6oEl0?si=dPtmTgyWvuB9ZcLr


Tony

From my book:

During the planning phase of this design, I used an Excel-based calculator that Dan Lott had specifically created for this task –calculating gas strut lengths and weights for teardrop hatches. You weigh the hatch and put that and its length into the calculator. It suggests the ideal attachment points, length, and weight rating for the springs.

If you do a search on the Teardrops and Tiny Travel Trailers forum (http://www.tntt.com) for “Hatch Gas Spring/Strut Calculator” you’ll find the calculator. For this build, the spreadsheet suggested a 27” gas spring. Using Sketchup CAD software, that length put the lower attachment point below the counter and thus wouldn’t work with my stove installation.

The next shorter springs I found have an extended length of 20.12”. Using Sketchup, I could see that they would work by attaching them above the countertop.

If you are not using my profile and galley layout–and if you don’t do CAD– you can use your template along with a hatch-end profile made from scrap to see what will work. Lay the two templates on the floor and use two sticks to mimic the open and closed strut lengths.
Here’s what the struts look like on this build with both the hatch open and closed:

You’ll note that I have room for my 5’ 9” height to access the galley, depending on the trailer frame height. Also note that the hatch is approaching the hinge’s maximum opening of about 95º.

To determine what spring weight you need, weigh and measure your hatch using Dan Lott’s diagram.

My upper attachment point (on the hatch) is 8-3/16” from the center of the hinge. With previous builds, I’ve used blocking built into the hatch frame. For this build, I made a bump-out on the hatch gusset to bolt the strut bracket to.

To find where to place the lower bracket, I drew two circles. The first was a 20.12” (12-1/8”) radius –that’s the extended length of the struts– from the upper attachment point of the open hatch.

The second radius 12.85” (12-7/8”) is drawn with the hatch closed. The compressed strut is 11.85”. To get that 12.85”number, I added an inch to the compressed strut to keep it from bottoming out during closing. Where these two arcs meet is the lower attachment point. Here’s what it looks like:

I hope this helps.

 

[JP2023]

Thank you Tony! I will take a look at your notes and see how it works!

 

[pistolriver]

Hello Tony, I cant thank you enough!!! I installed my hatch struts 3 times before I found your Gas Strut Calculator. I wont go into details as to the advice from experts that lead to 3 failure's, but useing your calculator worked the first time I applied my measurements. I cant tell you the relief I felt the first time I closed the hatch. It even helped pull it closed a little right before it is closed. Now my chore is to patch and hide the holes I made, lol. Thanks again, Good Job!!!