Unable to Create a Curve the way I want to

Salutations, SketchUp Users!

Before stating my situation, I feel the necessity of mentioning that I began working with SketchUp not too long ago, meaning that, much like my incapability of producing complex and intricate shapes and models, I am not very knowledgeable with all of SketchUp’s features (and, for that, I apologize).

I’ve been assigned to design a shock-absorbing base for a satellite that my workmates and I are building (it’s nothing too big, and I don’t think that’s very relevant to the problematic). With that in mind, I decided to start creating/modeling a honeycomb-inspired shape (not conceptualized by me, of course), and, as you can observe in the following hyperlink (https://imgur.com/a/FoLQV), I’d say I’m not too far out of what it truly is supposed to be (https://imgur.com/a/QpGZn). I have, however, been having several problems with the creation of this component: It is possible to deduce that, by comparing both the image of what my project looks like and what it should appear to look like, the curves aren’t exactly the same; not only that, but the dimensions (height, more predominantly) of my version don’t really look like the reference’s. I understand that these may seem like rookie problems (which they definitely are!), but without someone’s help, I don’t think ‘improvising’ my way out of this will turn out to be successful in any way.

I thank you for your collaboration and apologize for any inconveniences that I may be causing.

P.S. If you happen to also have suggestions in regards to what I should add/remove in order to make it more shock absorbing (it will be falling from the sky and hitting the floor at a high velocity), I’d be gratified.

Respectfully,
Fidalgo.

No need to apologize, all of us here in the community started somewhere and are here to help.

Looks like you are close. I do see that the example has a compound “bow” curve that flattens out at the ends so the spring ends enter the rigid frame at 90˚ to the downward force. This allows flex over the length of the spring and avoids little force hotspots or rotation moments at the intersection. In your simple arc model imagine that the force is applied in the center of the arc,in order for the arc to bend that intersection at the end of the arc has to act as a sort of rigid fulcrum and rotate downward.

Also, the stacked springs ( arcs above each other) are linked on center in the example. In your drawing the inner springs (lower on top and upper on bottom) are doing nothing and need to be tied to the outer springs on center to have any effect. Unless they are intended to provide a second spring rate at full compression of the outer springs?

It will be easier to help if you if you can include the file you are working on here. Seventh button across the top of the posting window is the upload button. Then we can see how you are working and if it’s easier to modify your drawing or start fresh. Do you have any dimensions of the original you are trying to copy or are you just working off of that picture?

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Thanks for replying!

It is true that no other springs are included in the picture, and my intention is to stack them (eventually); I believe that the way it is presented in the picture (with the actual, physical model) is good enough for the purpose at hand. As for the dimensions, no data regarding the dimensions has been acquired aside from the one you’re able to see in the picture, and those are the ones I’m utilizing. However, and this is something I believe is important, the whole “honeycomb” structure is supposed to fit within a radius of 32.5mm (I do not know if, after modeling, scaling down the complete, stacked springs would be a good way of making it fit).

I recognize how important the curves are, especially considering that this is supposed to work as a shock-absorber, so I’ll go ahead and post the project’s file, as asked. honeycomb.skp (1.5 MB)

Once again, I thank you for your cooperation.

Attentively,
Fidalgo.

I found this paper that has an equation for your curve:

Figure (2) shows this:

image

Figure (4):

image

where w(x) is given by:

image

Assuming you desire a ten-inch beam with one-inch deformation (the 0.5 below is this value divided by 2), the following equations can be used with the UV-PolyGen plugin:

x = u
y = 0.5 * (1.0 - Math.cos(2.0 * Math::PI * u / 10.0))
z = 0

where 0 <= u <= 10

image

The result:

The plugin can be found here: https://sites.google.com/site/spirixcode/code/uv_polygen.rbz

Here’s the model with the above: beam.skp (32.4 KB)

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Thank you so much, jimhami42!

This is precisely what I need, and I thank you for the research and assistance. You just solved my problem!

Also, I’m sorry for giving you all this work (which I now realize I should have done myself); I hope I wasn’t an inconvenience.

Graciously,
Fidalgo.

2 Likes

Not at all, @Fidalgo. I found it to be a fascinating project. I hope you don’t mind, but I created a single cell based on the documentation I found and uploaded it to the Warehouse. You can scale this component and replicate it into an overlapping array that will 3D print very nicely.

4 Likes

Way to go @jimhami42, above and beyond! I find this fascinating too.

@Fidalgo I understand that you were just representing once cell of what will eventually be a multi cell array. The “stacking” I was referring to is the two springs at top and the two springs at bottom of each cell that are stacked and tied together at center so that they can absorb and exert force together as a unit. In your model you are missing the center strut that ties the springs together so the inner springs are not acting. Only the outside spring will bend as a result of the downward force, see?

iK7bPju

Oh, I understand now what you mean, and, yes, it was a mistake on my end. I have it fixed now, thank you!
Regardless, based off of what you mentioned, I didn’t actually think that such a small part of the whole component could be so impactful, and it’s a relief to know that it has been solved.
Also, I should have understood what you meant the first time you said it, and I even feel bad for not having done so. Once again, thank you, endlessfix.

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Commendable job! What you did in a way that seems so natural and simple, I’ve been trying do, but struggling with everything while attempting to do it. Oh, and

I certainly don’t mind!

I have got a question, though, if you wouldn’t mind answering: Would ‘cutting’ the structure’s edges in order to make them have the same radius as that of a cylinder’s base affect the way the structure should behave? I can understand that, maybe, you won’t be able to supply me with an answer, but, perhaps, if you do happen to know, would you mind telling me?

Also, would it be possible if you told me how to acquire your model, through the Warehouse?

Once more, I thank you very, very much!

Respectfully,
Fidalgo.

No problem … just click on the Warehouse icon in my post and use the Download feature:

image

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That’s hard to answer since I’m not quite sure what your final design is supposed to look like. A sketch of the final result you want would help.

If you’re looking for a round version of this, maybe a round approach might work better:

One more iteration that’s more in line with your original design …

Yeah, I guess the way you’ve presented it would be more effective. But without proper testing, it seems hard to be certain, anyway. Would you say, however, that leaving the space inside the ‘casing’ empty would be better than prolonging the cells and filling it? I’m trying to go for a not very heavy structure, so, if leaving it hollow happens to be good, I’ll do exactly that.

Also, I know it’s rather annoying to be always asking it, but could you supply me with both versions of the round ‘honeycomb’? Don’t know if that’s asking for too much (sorry, if it is).

Attentively,
Fidalgo.

I’ve uploaded both of them to the Warehouse:

https://3dwarehouse.sketchup.com/user.html?id=1824658900641239202016828

Keep in mind that I’m just doodling around with the geometry. The stiffness ratio you’re looking for will need to be determined experimentally. The original model should roughly respond to the same force/deflection as documented in the paper, however.

Also, these should be printed in laser-sintered nylon for best results.

Thanks a lot for the input.
Also, yes, I realize that only through experimentation will I actually reach a concrete conclusion.

I intend on utilizing nylon for the effect, of course. Especially after having read more in-depth the document that you supplied (which will also be of great assistance).

I’ll be sure to keep posting, if I happen to find myself having to deal with a difficult problem, again.

Once more, I seriously apprize your help, and I just can’t thank you enough.

Respectfully,
Fidalgo.

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Great, keep us posted. If you print the real thing send a picture! Good luck.

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