Recessed gas struts for hatch

[_Ryan_]

I had an idea to recess the gas struts for the hatch into the hatch frame itself. An original problem with my design, which you can see in my design thread, was that my cabinets didn't leave enough room for the strut installation. I didn't want to redesign and give up vertical cabinet space to fit struts, and I also didn't want to cut a notch into the ends of the cabinets either. I think ith this solution I can get the best of both worlds.

As you can see I would double up the 3/4" ribs on either side of the hatch and cut a space for the strut to be installed. The struts I want to install are 3/4" in diameter so I will also take advantage of the 1/4" gap between the hatch and sidewall which will give me 1" of space.

I need a 70 degree angle for my hatch to open to the height so I had to figure out the open and closing length for the struts, 20" and 12" respectively. This puts the upper installation point 9 1/2" from the hinge. Also you cant see it here but the outer skin of the hatch will fully cover the struts and extend to the outer edge of the side walls. The inside skin will be trimmed to allow the struts to open and the hatch to extend.








I would love any comments or suggestions you might have. Thanks!

Ryan

[Thawley]

An original problem with my design, which you can see in my design thread, was that my cabinets didn't leave enough room for the strut installation. I didn't want to redesign and give up vertical cabinet space to fit struts, and I also didn't want to cut a notch into the ends of the cabinets either. I think ith this solution I can get the best of both worlds.

Perhaps I'm raising an obvious question, but could you not just mount the hatch-end to the hatch's inner panel and the other to the inside wall of the galley? Or to the cabinet frame above a door?

Your solution is VERY well engineered. It's also complex. The strut is exposed and in view whenever the hatch is open anyway. Your method seems to be best suited to conceal the stut when the hatch is closed, and no one can see it. This is an observation, not a criticism. I'm plenty sympathetic to (and often guilty of) putting design and craftsmanship above ease of construction. Either way, I can see you're gonna make it clean...

[_Ryan_]

An original problem with my design, which you can see in my design thread, was that my cabinets didn't leave enough room for the strut installation. I didn't want to redesign and give up vertical cabinet space to fit struts, and I also didn't want to cut a notch into the ends of the cabinets either. I think ith this solution I can get the best of both worlds.

Perhaps I'm raising an obvious question, but could you not just mount the hatch-end to the hatch's inner panel and the other to the inside wall of the galley? Or to the cabinet frame above a door?

Here's a better picture of the problem. The cabinets will be in the way if the strut is dropped much below the hatch frame. The plan is to attach the the sidewall at the bottom of the strut, and the side of the hatch frame at the top. To mount the strut flat to the underside of the inside skin it would have to be lowered. Does this answer your question or am I missing something?

Your solution is VERY well engineered. It's also complex. The strut is exposed and in view whenever the hatch is open anyway. Your method seems to be best suited to conceal the stut when the hatch is closed, and no one can see it. This is an observation, not a criticism. I'm plenty sympathetic to (and often guilty of) putting design and craftsmanship above ease of construction. Either way, I can see you're gonna make it clean...

Haha, yes it's complex and there is no benefit to hiding them but to solve my cabinet problem. The only advantage is that the bracket for the strut will be located higher on the sidewall and be slightly more out of the way, also it is the best way to keep it clean as you have said!

Thanks for the feedback! I always appreciate your insights.

[Thawley]

To mount the strut flat to the underside of the inside skin it would have to be lowered. Does this answer your question or am I missing something?

Yeah, I see now.

...The only advantage is that the bracket for the strut will be located higher on the sidewall and be slightly more out of the way, also it is the best way to keep it clean as you have said!

Got it. Other options would require different cabinet design or more rearward hinge location with shorter hatch. I think I'm on the same page, now.

[Thawley]

Just curious, what do you have planned for the "shelf" area between the galley cab and the interior cab? Open storage of some kind? I ask because it presents a usable horizontal surface – a magnet for clutter in my house. I can see myself inadvertently forgetting I'd set something there with the hatch open and then later closing the hatch on it without thinking. (I'm sure... I'm more prone to that than most.)

[_Ryan_]

If you are referring to the top of the upper cabinet in the galley then the answer is I'm not sure exactly. Probably place a wire rack to contain spices or other small things as I have seen in other builds. If you have any ideas let me know.

[Thawley]

Hydroponic herb garden. Duh...

[KCStudly]

My first thought was that the strut would not be doing anything, or very little, to help lift the hatch during the initial stages of opening due to it being pointed straight at the hinge. However, I am not too familiar with this style of strut. Are they progressive in their strength like a spring, or do they provide a fairly constant force?

I guess for a light weight hatch where the only concern is holding it up once open, that would do fine, but for a heavier hatch where assistance is needed to lift, maybe a problem.

That being said, I can't recall ever reading anyone say, "damn, I wish I had made my hatch weigh more."

"I should have built lighter", or "it came out heavier than I expected", yes, plenty of times.

By my way of thinking the strut would be much more effective if it was at 90 deg to a radii from the hinge when at mid stroke (assuming the force curve from the strut is close to linear).

You asked. These are my thoughts.

Again, great design work on the model/sketches.

[_Ryan_]

My first thought was that the strut would not be doing anything, or very little, to help lift the hatch during the initial stages of opening due to it being pointed straight at the hinge. However, I am not too familiar with these style of struts. Are the progressive in their strength like a spring, or do they provide a fairly constant force?

I guess for a light weight hatch where the only concern is holding it up once open, that would do fine, but for a heavier hatch where assistance is needed to lift, maybe a problem.

That being said, I can't recall ever reading anyone say, "damn, I wish I had made my hatch weigh more." "I should have built lighter", or "it came out heavier than I expected", yes, plenty of times.

By my way of thinking the strut would be much more effective if it was at 90 deg to a radii from the hinge when at mid stroke (assuming the force curve from the strut is close to linear).

You asked, these are my thoughts.

Again, great design work on the model/sketches.

I believe that the force applied is linear during the entire stroke, except for a damping at the end.

You have a great point about the angle. If it were 90 degress at mid stroke it would be better positioned for lifting throughout the entire movement. I'll play around with the angles and lengths and see what I get thanks!

[aggie79]

Ryan,

You are doing a fantastic job on your teardrop!

The way you have your struts oriented is the more traditional arrangement for teardrops. In most situations, this design works out well. However, in some cases, with the hatch closed, the struts are pushing up against the hatch and can cause either the hatch to bow and/or lift at the hurricane hinge.

After seeing Planovet's strut arrangement, I decided to do it his way. In the picture below, you can see that mounting point on the sidewall is closer to the bulkhead than the hatch mounting point and the hatch mounting point is aft of the sidewall mounting point.



In this arrangement, for the closed position, the force of the struts helps to keep the hatch closed and aligns with the structure. The downside of this arrangement is that it protrudes more into the galley area so you have to be sure that you clear both the upper cabinets - I offset mine - and the counter.

If I may, I'd like to offer one other item for thought. However, you design your strut arrangement, try too use a strut length for which there are many different pressure strengths available. For me, it was the third set that worked. (The first was too weak and the second was too strong.) If you design is uses a strut length for which there is just one strength available, you could be in for some serious re-working if that strength does not lift the hatch.

Regarding KC's question, my hatch lift seems progressive. The most effort - which there is very little - is at the closed position. At about midway, the struts exert enough force to lift the hatch by itself.

Take care,
Tom

[_Ryan_]

Ryan,

You are doing a fantastic job on your teardrop!

The way you have your struts oriented is the more traditional arrangement for teardrops. In most situations, this design works out well. However, in some cases, with the hatch closed, the struts are pushing up against the hatch and can cause either the hatch to bow and/or lift at the hurricane hinge.

After seeing Planovet's strut arrangement, I decided to do it his way. In the picture below, you can see that mounting point on the sidewall is closer to the bulkhead than the hatch mounting point and the hatch mounting point is aft of the sidewall mounting point.



In this arrangement, for the closed position, the force of the struts helps to keep the hatch closed and aligns with the structure. The downside of this arrangement is that it protrudes more into the galley area so you have to be sure that you clear both the upper cabinets - I offset mine - and the counter.

If I may, I'd like to offer one other item for thought. However, you design your strut arrangement, try too use a strut length for which there are many different pressure strengths available. For me, it was the third set that worked. (The first was too weak and the second was too strong.) If you design is uses a strut length for which there is just one strength available, you could be in for some serious re-working if that strength does not lift the hatch.

Regarding KC's question, my hatch lift seems progressive. The most effort - which there is very little - is at the closed position. At about midway, the struts exert enough force to lift the hatch by itself.

Take care,
Tom

Thanks tom!

I have gone back to the drawing board after doing some more research. I believe that I will use this positioning which will give me better force on the hatch and at the same time reduce the strength of the struts I will need to use. The attachment to the hatch will still be recessed but the sidewall attachment will not. I can still avoid my cabinets this way.



As far as your suggestion to use struts with many forces available I plan to order through McMaster at the following link. They have a wide variety of different lengths and force combinations. I did the design with part # 9416K2 and think I will start with #80 and see what happens. I will need to install them before the hatch is complete to get the angle correct, but if they turn out to be too weak I can return them later and upgrade to 90, 100, 110, 120, 130; all with the same dimentions. :-)

http://www.mcmaster.com/#gas-springs/=layidu

As far as strut force and installation the following links are packed with great info. Mounting with the shaft up ensures proper lubrication and less failures in the long run. Apparently in this position they provide a damping effect as well as the strut pushes through the oil at the end of the stroke. The force is indeed linear but slowly increasing throughout the stroke.

I have also given myself about 1/2" of extra room so that the strut will not be fully compressed. This will allow some extra insurance that the strut will not bottom out as well as make it a bit easier to install if my measurements are off in the slightest.

http://www.industrialgassprings.com/uk/calculate_basics.asp
http://www.stabilus.co.jp/fileadmin/docs/english/Print-brochures/Industry/Utility_Vehicles/Stab_Fahrzeugbau_06__GB_.pdf
http://www.dacoglu.com/desotocd/14_Body/Proprods-Technical_guide.pdf

[Jiminsav]

wanna know what I found out?..those struts put a damn big burden on whatever you mount them too..they just want to extend..they bent the hell out of the side walls they were attached too.

[_Ryan_]

wanna know what I found out?..those struts put a damn big burden on whatever you mount them too..they just want to extend..they bent the hell out of the side walls they were attached too.

Sorry to hear about your experience, but there are many here that have been successful using them in this way. Could you tell us what force struts you were using and how you had them mounted?

[KCStudly]

On a thin ply wall (1/2 inch thick or less) or true foamie (i.e. without suitable wood substructure) I could see this easily being the case (TLAR method).

I am currently in the throws of designing the gas strut option on TPCE and the forces and leverage involved are considerable (my other option is linear actuators with a completely different geometry). It would be entirely conceivable to bow a galley wall out on a lightly built TD with a heavy hatch or poor strut geometry.

It is for just this reason that I am considering looking closer at how Aggie79 Tom did his struts on the Silver Beatle. He has his wall mounted strut end very close to the bulkhead (nice and rigid) and the hatch side mounted far away from the hinge for a good leverage ratio on the hatch CG.

Hatch strut geometry is probably one of the more complicated aspects of the design process to grasp. I'm a mechanical engineer and I must admit that I am spending a fair amount of time studying and designing in my 3D model, even planning on looking at the FEA to verify forces and strut ratings.

I'd guess that for every build that I have read at least half did not get it right the first time, either in placement or in strut force rating. Even with careful study and my design resources, I am assuming that my results will be about the same odds.

Something to be said for a nice light weight hatch and simple fixed rod supports with tie down pins to prevent flipping over in the wind.