Request for help - a catenary

grzegorz_kondracki

Hi,
I often have to draw the power of the hoist using flat cables. As it is in the drawing.




These are a catenary. Now it draws with bows and lines but as I change the size of the overhang or spacing between the cable trolleys it spoils everything. Then I use sweet.


The second thing is a bit hard and boring work. In addition, the cables are twisted and it's just fun. How fast can you do and if you change the spacing etc. do not spoil and do it faster.

I was thinking about FeatureScript, sometimes I do my own featureScript, but I do not know whether it is with this handle, curves, tangency, etc. It would have to be similar to wire but for flat wires.

Maybe someone has an idea. You can do it "manually" but it is very time consuming and boring. Then change and red everything on sketch.

Grzegorz (Greg) Kondracki

michał_1

Hi Grzegorz, how about already existing 3D Spline script (https://cad.onshape.com/documents/573f7b36e4b02e83c71782fc/v/4e54a08374e12db1056f3bc2/e/5718da06c22e7b08a5fb58b3) and a sweep?
To drive 3D spline I draw semi-constrained frame:

 I'm sure you can find rules for the frame to constrain cable to update in desired way.
https://cad.onshape.com/documents/5b67de4c7e846adea64d7893/w/4b0cb527c4659e0dab414a41/e/48b1f0e6f9c867711b6122b7

PS. Miło zobaczyć kogoś z Polski.
Powodzenia
Michał

owen_sparks

@grzegorz_kondracki

Just to clarify are you looking to:-
(a) Change the design and have the cable update to the correct size
(b) Keep the existing design but have the cable rebuild as the trolleys move (keeping the total cable length the same).

I feel with some combination of the existing measure distance featurescript and some In-Context design either should be possible.

Regards OwS.

grzegorz_kondracki

Hi,

Thank you for your help. I did not think about the 3d Spline script - unless this solves my problem.

I will try and write about the results - it may be a little simplistic but probably enough.

Greg


PS. Dzięki Michał. Miło spotkać kogoś z Polski - teraz wiem, że nie jesteśmy sami :-)
Powodzenia
Grzegorz

michał_1

Some tests for in-context editing:

The cable length is incorrect, but it's due to the fixed angle of my driving frame. Angle should vary, and It would be a complex relation, rather.

ilya_baran

I think the solution depends on how accurate your catenaries need to be.  If the goal is largely visual, then Michał's solution is simple and makes sense.  If the goal is more accuracy, than computing the catenary equations in FeatureScript, sampling, and using opFitSpline, will give you much closer results (and better control over the lengths of your segments).

michał_1

That's a nice puzzle. I'm wondering if it's feasible when it's driven through an assembly.

Ben_Misegades

Don't forget that you can dimension the length of a Spline, that way you can have a "fixed" length of cable.

michał_1

@ben_misegades435 how that is? I know we can constraint ends of spline with dimension constraint, but not the length.

grzegorz_kondracki

Hi, now I had to work diligently on another matter but again i have a small problem again. I am now doing a preliminary project of a mobile port crane - I present it in the drawing. My problem is the rope on the fold. How to do it so that you can tilt the boom and rope properly behaved? In-Context and update? The rope between the jib and the crane changes and the rope descends from the pulley at the end of the jib - as we tilt the jib. Any ideas?

grzegorz_kondracki

Still a short film - jib movement

https://youtu.be/KjdKWM5Rw5A

michał_1

tangent mate?

michał_1

One more thing I'm wondering about, do you need these cables to behave naturally for any engineering purposes or it's just to impress the client?

Another thing, your file is public, you know now it's under MIT license (at least similar), anyone can use it for any purpose.

grzegorz_kondracki

I used the end of the jib and parallel but the rope is moving around the disc - you see the film.

In addition, it shows the rope route diagram - sorry for handwriting drawing

grzegorz_kondracki

Wires and ropes are needed in both cases. To show the customer and I have to do it quickly but in the future I would like to measure the length of a rope or cable. These are hard calculations and often a lack of cable or rope and especially for young engineers it gets problematic. He's counting and then I have to check it out.

michał_1

Only In-Context edit, and maybe some FS to calculate how much of a rope is hanging at the end. Of course length calculated when loaded only.

grzegorz_kondracki

A good idea. I also thought so. In the beginning of the in-context and 3d-spline - now I have to pre-draw it. Then I'll think about the exact calculation.

michał_1

Pulleys are not in line so it will be a lot of work to make it work.

Ben_Misegades

michał_1 said:

@ben_misegades435 how that is? I know we can constraint ends of spline with dimension constraint, but not the length.

Like so:

michał_1

Don't know how I came to the conclusion that this way I somehow specify the radius/curvature (at pike maybe). Now it sounds as ridiculous as it is. Thanks for the tip. Can we get something similar for arcs?

owen_sparks

@michał_1 you're not alone, I too thought you couldn't dimension a spline...

Ben_Misegades

I'm actually a little surprised that we can't already dimension arcs. In Solidworks you simply use the dimension tool and select both endpoints and the arc itself and you're given an arc length dimension...this doesn't seem to work in OS

I take it back, I just did it, somehow....stand by

Ben_Misegades

OK, so somehow it works by picking endpoints and the arc, but it seems very buggy and only works sometimes. I'm trying to figure out the exact workflow to get it to work, but I think an IR may be in order to make it work more consistently.

Ben_Misegades

OK, draw your arc, pick the dimension tool, select each endpoint of the arc, then hover the pointer over the arc, that seems to activate the arc dimension functionality

Paul_J_Premakumar

For more information on awakening dimensions : https://cad.onshape.com/help/#sketch-tools-dimension.htm