Gas Strut - ideal mounting position & Force Calculation

[Vatech]

TL;DR

A pair of gas springs is needed to be installed on a top opening aluminum extrusion frame.
The position methods differ. Motion results also.I am a computer engineer, this is out of my field so i would be thankful for some help.

I have a construction made from 4040 aluminum extrusion.
The top frame is opening at 90deg with external hinge.
the weight of the top is 6Kg
The dimensions are 50X75cm externally
and 42X67 internally (as the frame width is 4cm)
If pictures with dimensions would help please let me know.

 

[berkeman]

If pictures with dimensions would help please let me know

Yes, please. Diagrams/pictures always help.

 

[Vatech]

I was kind of in a hurry so i designed the basic structure to be able to select the stroke and length needed.
i found that a total legth of 342mm hardly matches, so the next length i found is 402mm which fits easilly.
About the force i though of buying adjustable air spring and remove pressure until i get the expected result. What do you think?
Also, thank you for your time.

 

[onatirec]

"Ideal" mounting position... It's not all that clear to me what you're asking.

To maximize the effectiveness of strut force, you'd want to increase the angle (i.e. move the bottom mount further towards the front of the enclosure) and keep the upper mounting point far away from the hinge...

In your drawing, it looks like the bottom mount point is quite close to the lid hinge. when the lid is closed, the force vector would be practically aligned with the surface of the lid, instead of perpendicular to it...

With enough force from the strut, the two positional considerations I mentioned above don't matter much.

 

[Vatech]

I need less force when the top is in open position . This means that the Bottom bracket of the strut would be reasonable close to hinge. When its in close position Yes , logically to be aligned with the top bracket would not help, that's why i is some cm below .
I am not an Engineer, that's why i come here for help.
By search on different installations i fould that on top opening applications they use that layout of bracket positions.
Just for reference :

 

[onatirec]

Because the angle of the lid is changing, there will almost certainly be less "opening" force when the lid is opened, compared to when it is closed.

The way you would check the adequacy of the force of the strut, is by decomposing the weight of the lid and strut force into vectors perpendicular to the lid and taking the moment about the hinge. Moment = force x distance. So you'll have something like mgcos(a)*d1 = F(strut,perpendicular)*d2.

The perpendicular component of the strut would be Fsin(b) as I have it drawn here, but it might be easier to define it from a different angle, depending on your actual placement.