159 lines
5.2 KiB
OpenSCAD
159 lines
5.2 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 <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 lower_bar_end_knuckle(chord=100, pivot_radius=12, rise=8,lat_skew=30) {
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l_body=chord * 1.5;
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w_body=pivot_radius * 2.5;
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h_axis=pivot_radius * 2.75;
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difference() {
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union () {
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translate([l_body/2, w_body/2, h_axis])
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rotate([0, 90, 0])
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cyl(h=l_body, r=w_body/2, rounding=5);
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// 'except=TOP' in phrase introduces the spurious hulls
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translate([l_body/2, w_body/2, h_axis*.75])
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cuboid([l_body, w_body, h_axis * .75], rounding=5);
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// bulge for wheel axle; the fork insertion end of
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// a lefty axle is 25mm diameter
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translate([chord * 0.25, w_body/2, 0])
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rotate([90, 0, 0])
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cyl(h=w_body, r=25, rounding=5);
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// fairing for this
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translate([chord * 0.25, w_body/2, -3])
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rotate([80, 0, 90])
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prismoid([w_body, 45], [w_body, 10], rounding=5, h=l_body * .75);
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}
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translate([ chord*0.25, -1, pivot_radius * 3])
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cube([chord, pivot_radius * 4, pivot_radius * 4]);
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// scoop for leg-bottom knuckle to rotate within
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translate([ chord*0.25, w_body/2, h_axis])
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rotate([0, 90, 0])
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cylinder(h=chord, r=pivot_radius * 1.3);
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// through hole for pivot axle
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translate([-1, w_body/2, h_axis])
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rotate([0, 90, 0])
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cylinder(h=l_body+2, r=pivot_radius/3);
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// through hole for wheel axle
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translate([ chord * 0.25, w_body +1, 0])
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rotate([90, 0, 0])
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cylinder(h=w_body-5, r=12.5);
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}
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// airfoil stub to be epoxied into the lower bar of
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// the linkage
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translate([chord*1.25, 1, 30])
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rotate([90 + rise, 360 - lat_skew, 0])
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airfoil(h=chord, L=2 - chord);
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// // brake disk
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// translate([(0 - (chord*1.25)), (l_hlb * cos(rise)), 1])
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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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// // wheel (obviously)
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// translate([(0 - (chord*1.25)), (l_hlb * cos(rise)), -10])
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// wheel();
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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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}
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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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translate([-125, 0, 0])
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color("blue")
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lower_bar_end_knuckle();
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translate([-100, 74, 0])
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wheel();
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translate([-100, 34, 0])
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color("silver")
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rotate([90, 0, 0])
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cylinder(h=1.5, r=75);
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// fourbar(length=1000, chord=100, long_skew=30, lat_skew=35, shoulder=650);
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// fourbar_axle_half(1000,100, 30); |