cardan joint or universal joint

[marti81]

Hello, everyone. I just joined this forum hoping to get a useful advice. I'm a civil engineer and I've been working on offshore structures for a couple of months. I work in London. My problem is as follows:

- imagine having an auction (not folding and always subject only to traction). I have to have two hinges to the two heads that allow me to rotation at least 35 degrees in all the vertical planes that have as rib the vertical passing for the lower head of the rod I thought to adopt two cardanic joints to the extremes. I realize that use is improper. I would like to know if first of all the cardanic joint can meet the requirements described above thinking that the lower joint will have an arm always firm and unable to rotate. the other arm will be constituted by the auction reached by means of the two pins and the cruise that characterize the cardanic joint.

If the answer is yes, I would like to know if it is feasible to these conditions:
- traction effort: 15000 kn = 15000000 n
- the first joint will be located at sea, at a depth beyond 100 m, while the second at a 20ina below the surface: I have good guarantees on its durability under such environmental conditions (salt water and sand) and no maintenance?

if you think you can make me give me references, directions, norms on how to design it? I imagine that I need to design the straffes in such a way that they do not collide when the main rod (it is a kind of rope) bends 35 degrees. the traction effort given is the maximum one, of course the joint will be subject to efforts of different intensity and in different directions, you understand well why. I think cmq that such joint can resist well fatigue.

I hope I've been clear and posted in the right section and I apologize if I didn't have to use the right technical terminology.

Thank you very much.

 

[gerod]

Hello and welcome.
It would take a pattern because in words I tried to understand the object you call argano but I lost myself.
send us a pattern that we see better. a drawing also by hand.
we are technical and we need drawings (or, if you prefer, drafts!:biggrin
Hi.

 

[cacciatorino]

but what do you have to do, a boa that follows the wavy motion but without possibility to rotate around its vertical axis? In this case, cardan can be the correct solution, problems are all technological of wear resistance and corrosion.

 

[Onda]

I believe that cardani are normally thought and sized to transmit twists and not tractions. I have never seen in a catalog of cardani the maximum transmissible force to traction but always and only the couple and the maximum number of turns.
It is also possible that there are cardani designed for this purpose, but I have never seen it.
it would perhaps be easier to use two pins placed at 90° between them to allow rotations on the two axes. seen also the forces at stake are relevant.


wave

 

[marti81]

here is the design

note the rods are distributed along the circumference of the platform. It's 8. cmq I just need the solution on one.

thanks for the help

 

[zeigs]

if the purpose is to make sure that the floating platform moves without turning something done as the cardan joint seems suitable to me, it is only to be dimensional to bear the effort. In my opinion if you calculate the bearings so as to endure the traction effort, you are already in the size of the cruise. more than roller bearings or ball bearings would look for bronzine and possibly stagne seals. Maybe a nice rubber head that wraps the joint and protects it both from water and sand.

I'm sorry about the size: I can also think of putting cardani to allow movement and prevent rotation, but on 100 meters of cable, because in the end it is to this that is comparable, the imho platform rotates that is a pleasure

question: how flexible is kevlar? Is it not possible to imagine fixing the rod to the foundation and to the platform rigidly at 90° and that I know, for the first meter, to cover it with a reinforcement that makes it bend with a defined minimum radius that prevents him from ripping? I'm thinking about a solution like compressor air tubes: for the first 10 cm are wrapped by a metal spiral that prevents the pipe from crushing at the attack. In this case you no longer have to deal with something that moves but only deforms elastically, so it is not affected by wear or corrosion. Maybe I wrote a caxxata, huh?

Hi.

 

[Onda]

if you use two staggered pins of 90° the second pin takes a stinging moment.
it is necessary to dimensional the fork for this moment inflection.
take a look at the nautical solutions, which of live cables are meant!http://www.oceanyachtsystems.co.uk/kevlar/kevlar_rigging.htmwave

 

[cacciatorino]

I believe that cardani are normally thought and sized to transmit twists and not tractions. I have never seen in a catalog of cardani the maximum transmissible force to traction but always and only the couple and the maximum number of turns.

This is because cardanic joints usually have a telescope to allow the recovery of distance variations between the flanges. In this case, there is no need for the mid-range joint to be eliminated.

 

[cacciatorino]

here is the design

note the rods are distributed along the circumference of the platform. It's 8. cmq I just need the solution on one.

thanks for the help

I believe that, from the cinematic point of view, the solution of the double cardanic joint is correct. to discard instead the cables if your goal is to keep the platform on the floor and prevent it from turning around the vertical axis (if you don't have these needs, I think you can proceed with the cables, as long as you go then you don't "around".
for the dimensionalization, two accounts should be made and see what runs out, it is not difficult to calculate the shooting on each pin, then once you choose the construction technology you make the measurements. more 'than other are worrying two data: the length of the trees (80 mt = how to maintain the bendings in acceptable values?) and the problem of corrosion. for the latter perhaps you would do well to ask in the "naval" section where you could find experienced people.

 

[marti81]

the solution with two staggered pins at 90 degrees was my first solution and the moment stinging on the other pin is not a problem but I would still avoid because fatigue is a bad beast. I'm trying to improve with the cardan joint. I realized that the sizing depends on construction technology. on the central tree constituted by the pull in kevlar there are no flexions. the bending there is in the terminal trees but are so short that the bending moment does not represent a big problem.

thanks to all

 

[Onda]

I remain of the idea that more than one cardan needs such an attack. as from attached image.

wave

 

[lollo3d]

I am not very experienced but the last wave image is beautiful and similar to a cardan, I cannot imagine what kind of forces are at stake in the middle of the sea, the force that can be applied to the surface of your platform, among which I also believe the compression of the tiranti. . .

 

[marti81]

There's no compression in the tie rods.

the image posted by wave is brilliant. I like it. The problem is that to apply it should listen to me about how to make the foundation attack. but they got caught up with something strange.

thank you very much to all and above all to wave for your commitment.

p.s.: I have a question for wave. Did you miss trying to dimensional it and the less you know how much it would weigh that kind of joint?

 

[Onda]

Hi, I'm glad you like my suggestion.
I didn't size it, but I just snapped to let you know what I had in mind.
If you want, and use solidworks, I can post it so that you can change it with the size you need. I just made sure that the size is "congruent" between them so that the final appearance was valid. By the way, it's not even a set but a multibody body, just to hurry!
If you don't have solidworks, I can post you an iges, so you can see it and think about it.
Keep in mind that I designed it as if the piece was made of machine, but it can also be done much more crudely with carpentry parts.
I imagine that the components that are located at the bottom of the sea have robust dimensions and are quite "free" of construction.
wave

 

[sampom]

There's no compression in the tie rods.

the image posted by wave is brilliant. I like it. The problem is that to apply it should listen to me about how to make the foundation attack. but they got caught up with something strange.

thank you very much to all and above all to wave for your commitment.

p.s.: I have a question for wave. Did you miss trying to dimensional it and the less you know how much it would weigh that kind of joint?

But now I'm curious about what that "half-water plate" might be. .:biggrin:

and then I didn't understand well: but are those "tiranti" rigid or just like cables?
and I'm always on fire because the platform "would be" floating if not bound and therefore always under the action of the hydrostatic thrust? in case you give us the maximum size and the material/thickness with which it will be realized?
and again;
in addition to the wave motion and currents which external factors determine the movement / oscillation of the platform? So you go back to the first, what do you need?? :biggrin:

greetings
Marco:smile:

 

[marcof]

There's no compression in the tie rods.

the image posted by wave is brilliant. I like it. The problem is that to apply it should listen to me about how to make the foundation attack. but they got caught up with something strange.

thank you very much to all and above all to wave for your commitment.

p.s.: I have a question for wave. Did you miss trying to dimensional it and the less you know how much it would weigh that kind of joint?

from the design that you have placed I have that piattafprma will rotate abundantly around the point of theoretical balance, lifting and lowering, with the tirants that will grow accordingly. if the rods climbed inclined from a larger (decisively wider) anchorage of the ri-imho platform the system would be decidedly more stable around the vertical rotation axis.
But I'm working on something else, so do a nice tara to what I wrote, because the rotation movement of the cables and consequent lowering of the platform I shaped it in mind:

Hi.

 

[MBT]

... I shaped it in mind:

Hi.

parametric or small??

:36_1_13::hahahah:

 

[marti81]

Excuse me, but don't ask me anything else about that structure. There is no platform or boa, there is something else I can't talk about. It's a prototype structure. it would be very useful to get the tools to change the design provided me kindly by wave that I thank again. I would have come to the same result if one of my friends hadn't bothered me at the supermarket where I was trying to figure out how the swiffer broom could be useful for that app :biggrin:. in fact the base has the same joint, as for the vacuum cleaners.

I'm asking for another aid. according to you an attack like the wave needs to be lubricated (even if I wonder how it can happen)? How can I estimate the lifespan of that wear-resistant attack (by preventing corrosion for the moment)? are peer review questions.

Thanks again, guys. You are great!!

I'm thinking whether to offer a stay in London by wave:wink:

 

[Onda]

to draw you can try to use alibre design express.
free: https://www.alibre.com/register/requestinfo.aspxI think that copn alibre you can open it, then you redesign it according to your needs.
if alibre was no more free there are others. Let me know.
As for wear, you should definitely use bronzine, bronze or synthetic materials. I would use the material with which the pins of the motorboat propellers are made, are lubricated by the same sea water. or the material with which the shells of the boats are made. always lubricated with sea water. There was a post in the naval section of this forum that spoke about it.

to estimate life you should estimate cycles, and then understand what movements are due to.
if they are waves you should take the "maps" of the wavy motion of the area with the periods in the various seasons and thus calculate the number of cycles. at that point, you can calculate the years of life, or if the design is infinite life, the minimum diameter of the pins.

as far as London is concerned. .
I was thinking about going through the New Year's Eve and going to find an old English friend.
But he's busy and so he'll be for another time.
Hi.

wave

 

[marti81]

Thank you very much.

I didn't know what the bushings were. I searched and found. As far as wear is concerned, I had understood the procedure but I would like to have an order of magnitude that may arise from your experience. for example you tell me: given that effort, assuming that it acts constantly and with this cyclicity you will have a wear of 2 mm in a year. But it does nothing. You helped me a lot. tomorrow I try the recommended program and I will try to open your files.

Thank you very much