Not very constructive comments. Not helpful. Adrian Mariano wrote: > Also, cutting and pasting answers from your code back into the code is > never the answer. Imagine if you had to do that 1000 times to get to the > solution you wanted---just not practical. That’s not at all what I had in mind. I said …using a function or whatever…

I calculate beziers of a specific length or minimum z value to model cable strips for a 3D printer. The code is here: https://github.com/nophead/NopSCADlib/blob/master/utils/bezier.scad. The code is specific for U shaped curves but the technique could probably be adapted for other shapes. To get the length I just evaluate 100 points and sum the distances between them. To change the length I move the inner two control points up or down using Newton Raphson. On Tue, 21 Apr 2026 at 03:02, Caddiy via Discuss <discuss@lists.openscad.org> wrote: > Not very constructive comments. Not helpful. > > Adrian Mariano wrote: > > Also, cutting and pasting answers from your code back into the code is > never the answer. Imagine if you had to do that 1000 times to get to the > solution you wanted---just not practical. > > That’s not at all what I had in mind. > > I said …using a function or whatever… > > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org

revised one Change in the length is negligible. [image: Screenshot 2026-04-21 at 10.26.54 PM.png] But it's not an openscad code. Hard coded openscad file attached python code: from openscad4 import * a=arc(30,20,70) b=rot2d(90,a) # center cam driving the piston rods, there are 21 positions defined s1=[ [a[i],b[i],[0,0]] for i in range(len(a))] # defining control points for bezier "cp2" are control points and "cp3" is bezier cp1=[mirror_line(c23([a[i],b[i]]),c23(line_as_axis([a[i],b[i]])),a[i]+[0]) for i in range(len(s1))] cp2=[p+[[100,19,0],[120,19,0],[200,19,0]] for p in cp1] cp3=[ bezier(p,20) for p in cp2] # center line of cylinder l1=[[-200,19],[200,19]] # length of the piston rod 157 (starts at 3 and ends at 160) with 51 points l2=m_points1_o([[0,3],[0,160]],50) # super-imposing the line l2 over beziers cp4=[ wrap_around(l2,p) for p in cp3] # same is repeated for the left side cp5=[mirror_line(c23([b[i],a[i]]),c23(line_as_axis([a[i],b[i]])),b[i]+[0]) for i in range(len(s1))] cp6=[p+[[-100,19,0],[-120,19,0],[-200,19,0]] for p in cp5] cp7=[ bezier(p,20) for p in cp6] cp8=[ wrap_around(l2,p) for p in cp7] # calculation for length and end point position lx=[l_lenv_o(p) for p in cp4] # length of the rod xv=[ p[-1][0] for p in cp4] # end point of the rod for 51 different positions fo(f''' //center line of cylinder %color("grey",.3) p_line3d({l1},.3); //cam color("blue") for(p=[s1[abs(round(20*sin($t*180)))]])p_line3dc(p,1); //initial bezier on which the line l2 is super-imposed //color("magenta") for(p=[cp3[abs(round(20*sin($t*180)))]])p_line3d(p,1); //right side piston rod color("black") for(p=[cp4[abs(round(20*sin($t*180)))]])p_line3d(p,1.1); // left side piston rod color("black") for(p=[cp8[abs(round(20*sin($t*180)))]])p_line3d(p,1.1); // text for line length color("magenta") translate([30,50,0])rotate([0,0,0])linear_extrude(0.05) text(str("line_length : ",lx[abs(round(20*sin($t*180)))]),10); // text for end point position color("magenta") translate([30,70,0])rotate([0,0,0])linear_extrude(0.05) text(str("end_point : ",xv[abs(round(20*sin($t*180)))]),10); // calculation in python and hard coded points in openSCAD s1={s1}; //center cam cp3={cp3}; //original bezier cp4={cp4}; // super-imposed piston rod on bezier rhs cp8={cp8}; // super-imposed piston rod on bezier lhs lx={lx}; // line lengths xv={xv}; // end positons ''') On Mon, 20 Apr 2026 at 20:33, Sanjeev Prabhakar <sprabhakar2006@gmail.com> wrote: > Code can be written in more comprehensive manner later. > > First point is whether this is the correct understanding of the problem. > > If this is correct, exact bezier length can be modeled as per me. > > Now does it stop here, only in 1 plane e.g. this is in x-z plane or the > entire thing has to be rotated around x-axis as well. > > More interesting would be to understand the purpose, it feels like an NVH > (Noise Vibration and Harshness) simulation of a beam. > > Thanks > > > > > > On Mon, 20 Apr, 2026, 10:37 am Caddiy via Discuss, < > discuss@lists.openscad.org> wrote: > >> Sanjeev Prabhakar wrote: >> >> Maybe this comes closer[image: Screenshot 2026-04-20 at 8.18.59 AM.png] >> >> How do you get all those numbers? Could be useful for complex 3D surfaces. >> >> Nice constant-length bezier, but the code is beyond me! >> >> It would be nice to be able to get the difference between the actual >> length of the bezier, and what it should be, and feed that as a correction >> back into the bezier. But I think it would make the computer go round and >> round in ever-decreasing circles. >> >> However, it could be done with two identical beziers, a “real” one and a >> “dummy”. The dummy calculates the correction and that is fed not back into >> the dummy but into the real bezier, using a function or whatever. I’m just >> wondering whether both beziers can be obtained from a single module, or >> whether the dummy would have to be cut and pasted from the real one. Is >> that mathematically permissible? >> >> I’ll try it out tomorrow. >> _______________________________________________ >> OpenSCAD mailing list >> To unsubscribe send an email to discuss-leave@lists.openscad.org > >