Swining Bridge

[Red]

Is it possible to script a tube/cylinder to be 30’ long and sag down in the mid 2’? What I’m using it for is a swinging bridge. Or is there a better way to achieve this?

[Frank Beister]

Have you ever used the tube-command? This should work with a calculated path for the tube.

[Frank Beister]

I gave it a try. See attached object.

The solution is TUBE indeed. The shape is a cylind, the path is a parable, as we know at least since Antonio Gaudi. Which order is the most real I don't know, but I took (for not doing too much math) the second order:

y = aa * x^2

By knowing 2 Points (left and right hight L and R) and their distance (width of object A) you can calculate the factor aa by:

aa= R / ( (A*SQR(R/L)/(1+SQR(R/L) )^2

P.S. For getting a feeling to the system of the parable I found a nice link:
Parable calculation

[Anonymous]

you could also make it very easily using trussmaker



bill

[Red]

Thanks to you both. I will try your part out. Also I never thought about trussmaker!

[gerd]

... or you can also try the profiler, but hen you have to draw the parabel by yourselve, what is not easy without gdl (same problem with trussmaker).

and gdl is much more elegant!

@ F.Beister:
if I remember right, the form of the parabel depends also on the weight of the cable (kg/m) (and G of course). this may be a more or less useful addition to your nice gdl!
a further idea: the parabel calculation could be also used inside the tentmaker object. perhaps a little more realistic than sin/cos method, but in most cases this will not be recognized.

best regards!

[Frank Beister]

Hello Gerd.

if I remember right, the form of the parabel depends also on the weight of the cable (kg/m) (and G of course). this may be a more or less useful addition to your nice gdl!

Formulas. Give me formulas Or a link to the physics.

a further idea: the parabel calculation could be also used inside the tentmaker object. perhaps a little more realistic than sin/cos method, but in most cases this will not be recognized.

Thats right. SIN/COS is not the kings way. I have seen this and discussed with zzyzx, I think you know him by the german talk. Tentmaker is nice and was pretty improved by the users. The single working object in the spirit of openGDL. 😉 But it has limited options, because it creates the surface by its border.

I have started an object, which draws a mesh with caculated hights by primitives. If I can solve some basic problems it will be possible to have some points inside the tent/surface to risen it. Splines are nothing else than quadric equations by a higher order. I have a link to a solution in 2D, but still missing the transfer to 3D. It is my aim to make curved surfaces, parametric and with moveable hotspots.

[Red]

I ended up going the trussmaker route and using solid element operations.

[Anonymous]

i'm pretty sure that the shape of the parabola does not depend on the weight of the cable

otherwise the inverted models that Gaudi made from chains (i think) to calculate the most efficient structure for Sagrada Familia wouldn't have worked



bill

[Red]

Truthfully is model will be imported into 3d max to be tweaked and then it’s going into a Battlefield 2 Mod. I will forever be a gamer.