Formula for determining the placement of gas shocks on hatch

[Mike C.]

Thanks for the help you all have offered, but with Miriam's health issues on my mind, I haven't really had time to respond.

I will review this and see what we can do.

Thanks

[angib]

Miriam (and Mike), I'm wishing you well and hope you get good news soon.

In the meantime, I thought I'd leave this work where you can find it, while I remember that I've done it (which may last for, ooh, minutes....).

In positioning struts, you have to think of their 'hatch down' position as well as their 'hatch up' position. Here's a diagram of how that works on your yellow 48" strut example:



When you close the hatch, the hatch end of the strut, point A, swings down around the hatch hinge and ends up at point B (see - proper jommitry, wiv' letters an' all). So your 48" (extended) strut has now compressed down to about 6" long, which is impossible - a strut can only compress down to a little over half its extended length.

All of the examples you drew suffer from this same problem. So, what can be done? Here is one solution, if you can find 60" (extended) struts:



I bet 60" struts are made, though sourcing them may be difficult - you might try any truck body builders in your area, as they might use them.

But this will only lift the hatch as high as you have it in the photo - and I'm guessing you wanted it to go higher than this, but you didn't have a longer step ladder handy!

As I can roughly work out the leverage from this diagram, I'd say you would need struts (one each side, yeah?) each rated at between 2 and 2.5 times the weight you get if you put your bathroom scales on top of the step ladder and weight the end of the hatch.

Andrew

[Miriam C.]

Ahhhh Andrew you amaze me. I will think about 60". We have a lot of truck industry here. You are right in assuming we want the hatch higher but have not a bigger ladder. Besides I cannot lift it higher anyway. I did the measurements with Mike holding the ladder in position so they are in fact correct. We propped it again so I could make visible markers. The measurements are correct for the space as needed but for reference only and dont' reflect where the strut has to go.

I really appreciate your information. It will make is easier to know what to find. Napa had some pretty long struts and the boating industry has some too. I can also remake that end of the cabinet some. Still need to raise it and be sure it will clear the inlet. The 120vac can be moved.

[angib]

So here is plan C (or is it D?). Boating is probably a good source of longer struts - their engine bay hatches are often much bigger and heavier than teardrop hatches. And you can decide to let Christmas come early and treat yourselves to the electrically powered hydraulic type that will open themselves, like Len's Slumbercoach.....

To make a 60" strut open the hatch higher than it does in the previous post, the hatch end has to be moved nearer to the hinge. That means you have to notch the corner of the cabinets you've made, but it's either that or not lifting the hatch as high. I think this is about high enough to clear your head on the end of the hatch - you want it only 'high enough', so that you can still reach it to pull it down.



The leverage is about 1:4 between the struts and the end of the hatch, so I would suggest you try a pair of struts with a rating at least 3 times the weight of the end of the hatch - you may want to go nearer to 4 times the hatch end weight to get a really positive lift - let's say that's where you have to pull down on the end of the hatch with a force of 100 pounds to get it to close.

Andrew

[Mike C.]

Andrew,

I appreciate the help with Plan C or was it D, well anyway it looks like all I need to do, is find two realy long struts with a large lift capacity and position them as close to the marks you made and I am home free.

Now on to the internet to find such.

So, again thank you for your detailed drawings and technical expertise. We may talk more as we get into the project and I have the lift shocks in hand.

[angib]

...well anyway it looks like all I need to do, is find two realy long struts...

You also need to find a good-sized metal bucket - I reckon you can balance that on top of the steps, to get the hatch to open as far as you want it to.....

Andrew