Simon Brooke
35376827d1
I'm still having problems with fudge factors which I need to resolve; I need to learn more about filletting, rounding, radiusing and fairing.
103 lines
3.2 KiB
OpenSCAD
103 lines
3.2 KiB
OpenSCAD
// fourbar.scad
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// (c) Simon Brooke 2025; CC-BY-SA
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include <BOSL2/std.scad>
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include <NACAAirfoils/files/Naca4.scad>
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include <library/skew.scad>
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include <lowerknuckle.scad>
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include <wheel.scad>
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$fn=64;
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// Wherever you see unexplained numbers in this file, they are
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// fudge because I don't yet properly understand the coordinate
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// transforms and can't remember enough of the trigonometry I
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// learned 60 years ago. There REALLY should not be any unexplained
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// numbers.
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module fourbar_leg(length=1000, chord=100, lat_skew=35, long_skew=30) {
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h = length * cos(lat_skew) * cos( long_skew);
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w = length * sin( lat_skew);
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d = length * sin( long_skew);
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pivot_radius = 12;
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translate([0, 0-w, 0]) {
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// upper pivot needs a complex trig transformation!
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translate([d - (chord/2), w, h + chord])
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rotate([0, 90+long_skew, 0])
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color("black")
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cylinder(h=chord, r=12);
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// lower pivot:
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translate([0 - chord, 0, (chord/2 * sin(long_skew))])
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rotate([0, 90+long_skew, 0])
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color("black")
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difference() {
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cylinder(h=chord, r=12);
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// through hole for pivot axle
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translate([0, -1, 0])
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cylinder(h=chord+2, r=pivot_radius/3);
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}
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// aerofoil section
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sskew([0, long_skew, 0, 0, 0, 0])
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rotate([lat_skew, 0, 180])
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color("black")
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airfoil(h=length, L=chord);
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}
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}
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module fourbar_axle_half( length=1000, chord=100, lat_skew=35, long_skew=30, shoulder=650) {
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rise=8;
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// I've got something wrong in computing the half-lower-bar
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// length, and I don't know what. It scales with lat_skew, but
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// (unsurprisingly) not liniarly. Fudge of 23 works for lat_skew of 30; 34 works for lat_skew of 35
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fudge=0;
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w = ((length * cos(lat_skew) ));
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l_hlb= w * (1/cos(rise)) + fudge;
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v_offset=(l_hlb * sin(rise)) + 38;
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translate([-15, 0, 0 - v_offset])
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rotate([90-rise, 0, 180])
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color("black")
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airfoil(h=l_hlb, L=chord);
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// lower knuckle
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rotate([0, long_skew, 0])
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translate([(0 - (chord*1.25)), (l_hlb * cos(rise) + 72), -62])
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lower_bar_end_knuckle(chord, 12, rise, lat_skew);
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rotate([0, long_skew, 0])
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translate([(0 - (chord*1.25)), (l_hlb * cos(rise) + 155), -62])
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wheel();
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rotate([0, long_skew, 0])
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translate([(0 - (chord*1.25)), (l_hlb * cos(rise) + 115), -62])
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rotate([90, 0, 0])
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color("silver")
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cylinder( h=1.5, r=75);
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}
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module fourbar(length=1000, chord=100, lat_skew=30, long_skew=30, shoulder=650) {
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translate([0, 0-(shoulder/2), 0])
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fourbar_leg( length, chord, lat_skew, long_skew);
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translate([0, (shoulder/2), 0])
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mirror([0, 1, 0])
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fourbar_leg(length, chord, lat_skew, long_skew);
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fourbar_axle_half(length, chord, lat_skew, long_skew, shoulder);
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mirror([0, 1, 0])
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fourbar_axle_half(length, chord, lat_skew, long_skew, shoulder);
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}
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// fourbar(length=1000, chord=100, long_skew=30, lat_skew=35, shoulder=650);
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// fourbar_axle_half(); |