Start made on the four-bar linkage. I need to remember trigonometry.

model/Library/NACAAirfoils/LICENSE.txt

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+This thing was created by Thingiverse user Parkinbot, and is licensed under Creative Commons - Attribution - Non-Commercial

model/Library/NACAAirfoils/README.txt

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+NACA Airfoils - 4 digit fully parametric OpenSCAD library  by Parkinbot on Thingiverse: https://www.thingiverse.com/thing:898554
+
+Summary:
+Are you playing around with airfoils? Better have a fast airfoil data generator at hand. I found some code doing airfoils in this forum, but that wasn't flexible enough as it didn't take advantage of the new vector features of OpenSCAD 2015.So I coded my own little library to always have a fully customizable 4 digit NACA airfoil data generator at hand.   What you geta fully parametric library  a bunch of usage examples  help functionality  well documented code (but very tough in the core part)  In my next post I'll show how to do objects that sweep smoothly between different airfoil types being freely shifted and rotated in 3D space. Stay tuned.   

model/Library/NACAAirfoils/files/Naca4.scad

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+// Naca4.scad - library for parametric airfoils of 4 digit NACA series
+// Code: Rudolf Huttary, Berlin 
+// June 2015
+// commercial use prohibited
+
+
+// general use: for more examples refer to sampler.scad
+// naca = naca digits or 3el vector  (default = 12 or [0, 0, .12])
+// L    = chord length [mm]      (default= 100)
+// N    = # sample points        (default= 81)
+// h    = height [mm]            (default= 1)
+// open = close at the thin end? (default = true)
+// two equivalent example calls
+// airfoil(naca = 2408, L = 60, N=1001, h = 30, open = false); 
+// airfoil(naca = [.2, .4, .32], L = 60, N=1001, h = 30, open = false); 
+
+module help_Naca4()
+{
+  echo(str("\n\nList of signatures in lib:\n=================\n", 
+  "module help() - displays this help\n",
+  "module help_Naca() - displays this help\n",
+  "module help_Naca4() - displays this help\n",
+  "module airfoil(naca=2412, L = 100, N = 81, h = 1, open = false) - renders airfoil object\n", 
+  "module airfoil(naca=[.2, .4, .12], L = 100, N = 81, h = 1, open = false) - renders airfoil object using percentage for camber,  camber distance and thicknes\n", 
+  "function airfoil_data(naca=12, L = 100, N = 81, open = false)\n",
+  "=================\n")); 
+}
+
+module help() help_Naca4(); 
+
+// help(); 
+// this is the object
+module airfoil(naca=12, L = 100, N = 81, h = 1, open = false)
+{
+  linear_extrude(height = h)
+  polygon(points = airfoil_data(naca, L, N, open)); 
+}
+
+// this is the main function providing the airfoil data
+function airfoil_data(naca=12, L = 100, N = 81, open = false) = 
+  let(Na = len(naca)!=3?NACA(naca):naca)
+  let(A = [.2969, -0.126, -.3516, .2843, open?-0.1015:-0.1036])
+  [for (b=[-180:360/(N):179.99]) 
+    let (x = (1-cos(b))/2)  
+    let(yt = sign(b)*Na[2]/.2*(A*[sqrt(x), x, x*x, x*x*x, x*x*x*x])) 
+    Na[0]==0?L*[x, yt]:L*camber(x, yt, Na[0], Na[1], sign(b))];  
+
+// helper functions
+function NACA(naca) = 
+  let (M = floor(naca/1000))
+  let (P = floor((naca-M*1000)/100)) 
+  [M/100, P/10, floor(naca-M*1000-P*100)/100];  
+
+function camber(x, y, M, P, upper) = 
+  let(yc = (x<P)?M/P/P*(2*P*x-x*x): M/(1-P)/(1-P)*(1 - 2*P + 2*P*x -x*x))
+  let(dy = (x<P)?2*M/P/P*(P-x):2*M/(1-P)/(1-P)*(P-x))
+  let(th = atan(dy))
+  [upper ? x - y*sin(th):x + y*sin(th), upper ? yc + y*cos(th):yc - y*cos(th)];
+
+

model/Library/NACAAirfoils/files/Sampler.scad

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+// Sampler.scad - library for parametric airfoils of 4 digit NACA series
+// Code: Rudolf Huttary, Berlin 
+// June 2015
+// commercial use prohibited
+
+ use <ShortCuts.scad>  // see: http://www.thingiverse.com/thing:644830
+ use <Naca4.scad>
+ 
+place_in_rect(110, 70) // arange that stuff in a grid
+{
+// duct
+  T(50, 30, 0)
+  rotate_extrude($fn = 100)
+  translate([30, 100, 0])
+  R(0, -180, 90)
+  polygon(points = airfoil_data([-.1, .4, .1], L=100)); 
+
+// drop
+T(50, 30, 0)
+scale([1, 2])
+rotate_extrude()
+Rz(90)
+difference()
+{
+  polygon(points = airfoil_data(30)); 
+  square(100, 100); 
+}
+
+// some winding airfoils
+linear_extrude(height = 100, twist = 30, scale = .5)
+  polygon(points = airfoil_data(30)); 
+
+translate([50, 0, 0])
+linear_extrude(height = 100, twist = 30, scale = .5)
+translate([-50, 0, 0])
+  polygon(points = airfoil_data(30)); 
+
+translate([100, 0, 0])
+linear_extrude(height = 100, twist = 30, scale = .5)
+translate([-100, 0, 0])
+  polygon(points = airfoil_data(30)); 
+
+T(30)
+ airfoil(naca = 2432, L = 60, N=101, h = 30, open = false); 
+
+// some airfoil objects, Naca values defined with number or vector
+ airfoil ();                  // NACA12 object 
+ airfoil (2417);              // NACA2417 object 
+ airfoil ([.2, .4, .17]);     // NACA2417 object 
+ airfoil ([-.10101, .52344, .17122]); // inverted precise curvature
+
+help();  // show help in console
+
+// end of sampler
+
+}
+
+
+
+

model/Library/NACAAirfoils/files/ShortCuts.scad

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+// ShortCuts.scad 
+// Autor: Rudolf Huttary, Berlin 2015
+//
+$fn = 100; 
+
+
+//show_examples(); 
+
+module show_examples()
+	place_in_rect(30, 30)
+	{
+		Cy(h = 10); 
+		CyH(h = 10); 
+		CyH(h = 10, w = 30); 
+		CyS(h = 10); 
+		CyS(h = 10, w1 = 25, w2 = 75); 
+		Cu(10); 
+		Ri(h = 10); 
+		RiH(h = 10); 
+		RiS(h = 10, w1 = 10); 
+		RiS(h = 10, w1 = 30, w2 = 300); 
+		Sp(); 
+		SpH(10, 30, 30); 
+	}
+
+
+
+module help()
+{
+echo("==============="); 
+echo("help(): shows this help"); 
+echo("show_examples(): shows some examples"); 
+echo("place_in_rect(): places children objects in grid"); 
+echo("Transformations:"); 
+echo(" transform :  T(x=0, y=0, z=0), Tx(x=0) , Ty(y=0), Tz(z=0)"); 
+echo(" rotate :  R(x=0, y=0, z=0), Rx(x=0) , Ry(y=0), Rz(z=0)"); 
+echo(" scale :  S(x=1, y=1, z=1), Sx(x=1) , Sy(y=1), Sz(z=1)"); 
+echo("Logical"); 
+echo(" difference :  D()"); 
+echo(" union :  U()"); 
+echo(" intersection : *missing*"); 
+echo("Primitives"); 
+echo(" circle :  Ci(r=10)"); 
+echo(" circle_half :  CiH(r=10, w=0)")
+echo(" circle_segment :  CiS(r=10, w1=0, w2=90)")
+echo(" square :  Sq(x=10, y=0, center=true))"); 
+echo(" cylinder :  Cy(r=10, h=1, center=true)"); 
+echo(" cylinder_half :  CyH(r=10, w=0)")
+echo(" cylinder_segment: CyS(r=10, h=1, w1=0, w2=90,center=true)"); 
+echo(" cylinder_segment: Pie(r=10, h=1, w1=0, w2=90,center=true)"); 
+echo(" cube :  Cu(x=10, y=0, z=10, center=true)"); 
+echo(" ring :  Ri(R=10, r=5, h=1, center=true)"); 
+echo(" ring_half :  RiH(R=10, r=5, h=1, w=0 center=true)"); 
+echo(" ring_segment :  RiS(R=10, r=5, h=1, w1=0, w2=90, center=true)"); 
+echo(" sphere:  Sp(r=10))"); 
+echo(" sphere_half:  SpH(r=10, w1 = 0, w2 = 0))"); 
+echo("==============="); 
+}
+
+
+// Euclidean Transformations
+
+module T(x=0, y=0, z=0){translate([x, y, z])children(); }
+module Tx(x) { translate([x, 0, 0])children(); }
+module Ty(y) { translate([0, y, 0])children(); }
+module Tz(z) { translate([0, 0, z])children(); }
+
+
+module R(x=0, y=0, z=0){rotate([x, y, z]) children();}
+module Rx(x=90){rotate([x, 0, 0]) children();}
+module Ry(y=90){rotate([0, y, 0]) children();}
+module Rz(z=90){rotate([0, 0, z]) children();}
+
+module S(x=1, y=1, z=1){scale([x, y, z]) children();}
+module Sx(x=1){scale([x, 1, 1]) children();}
+module Sy(y=1){scale([1, y, 1]) children();}
+module Sz(z=1){scale([1, 1, z]) children();}
+
+
+module D() difference(){children(0); children([1:$children-1]);}
+module U() children([0:$children-1]);
+// module I() intersection()children([0:$children-1]); // does not work for some reason
+
+
+// primitives - 2D
+
+module Sq(x =10, y = 0, center = true)
+{
+   if(y==0)
+		square([x, x], center = center); 
+	else
+		square([x, y], center = center); 
+}
+module Ci(r = 10)
+{
+	circle(r = r); 
+}
+
+// derived primitives - 2d
+module CiH(r = 10, w = 0)
+  circle_half(r, w); 
+
+module CiS(r = 10, w1 = 0, w2 = 90)
+  circle_segment(r, w1, w2); 
+
+
+// primitives - 3d
+module Cy(r = 10, h = 1, center = true)
+{
+	cylinder(r = r, h = h, center = center); 
+}
+module Cu(x = 10, y = 0, z = 10, center = true)
+{
+  if (y==0)
+	cube([x, x, x], center = center); 
+  else
+	cube([x, y, z], center = center); 
+}
+
+// derived primitives - 3d
+module CyH(r = 10, h = 1, w = 0, center = true)
+  cylinder_half(r, h, w, center); 
+
+module CyS(r = 10, h = 1, w1 = 0, w2 = 90, center = true)
+  cylinder_segment(r, h, w1, w2, center); 
+
+module Ri(R = 10, r = 5, h = 1, center = true)
+  ring(R, r, h, center); 
+
+module RiS(R = 10, r = 5, h = 1, w1 = 0, w2 = 90, center = true)
+   ring_segment(R, r, h, w1, w2, center); 
+
+module RiH(r1 = 10, r2, h = 1, w = 0, center = true)
+   ring_half(r1, r2, h, w, center); 
+module Pie(r = 10, h = 1, w1 = 0, w2 = 90, center = true)
+  cylinder_segment(r, h, w1, w2, center);  
+module Sp(r = 10)
+  sphere(r); 
+module SpH(r = 10, w1 = 0, w2 = 0)
+  sphere_half(r, w1, w2); 
+module SpS(r = 10, w1 = 0, w2 = 90, w3 = 90)
+  sphere_segment(r, w1, w2); 
+
+
+
+
+// clear text definitions
+module circle_half(r = 10, w = 0)
+{
+	difference()
+	{
+		circle(r); 
+     rotate([0, 0, w-90])
+     translate([0, -r])
+		square([r, 2*r], center = false); 
+	}
+}
+
+module circle_segment(r = 10, w1 = 0, w2 = 90)
+{
+  W2 = (w1>w2)?w2+360:w2; 
+  if (W2-w1 < 180)
+    intersection()
+		{
+       circle_half(r, w1); 
+       circle_half(r, W2-180); 
+ 		}
+	else
+    union()
+		{
+       circle_half(r, w1); 
+       circle_half(r, W2-180); 
+ 		}
+}
+
+module cylinder_half(r = 10, h = 1, w = 0, center = true)
+{
+  linear_extrude(height = h, center = center)
+  circle_half(r, w); 
+} 
+
+module cylinder_segment(r = 10, h = 1, w1 = 0, w2 = 90, center = true)
+{
+  linear_extrude(height = h, center = center)
+  circle_segment(r, w1, w2); 
+} 
+
+module ring(R = 10, r = 5, h = 1, center = true)
+{
+	difference()
+	{
+	cylinder(r = R, h = h, center = center); 
+   translate([0, 0, -2*h])
+	cylinder(r = r, h = 4*h, center = false); 
+	}
+}
+
+module ring_half(R = 10, r = 5, h = 1, w = 0, center = true)
+{
+	difference()
+	{
+		ring(R, r, h, center); 
+     rotate([0, 0, w])
+     translate([0, -R/2, 0])
+		cube([2*R, R, 3*h], center = true); 
+	}
+}
+
+module ring_segment(R = 10, r = 5, h = 1, w1 = 0, w2 = 90, center = true)
+{
+  W2 = (w1>w2)?w2+360:w2; 
+  if (W2-w1 < 180)
+    intersection()
+		{
+       ring_half(R, r, h, w1, center); 
+       ring_half(R, r, h, W2-180, center); 
+ 		}
+	else
+    union()
+		{
+       ring_half(R, r, h, w1, center); 
+       ring_half(R, r, h, W2-180, center); 
+ 		}
+}
+
+
+module sphere_half(r = 10, w1 = 0, w2 = 0)
+{  
+	difference()
+	{
+   	sphere(r); 
+      rotate([-w1, -w2, 0])
+     	translate([0, 0, r])
+		cube(2*r, 2*r, r, center = true); 
+	}
+
+}
+
+
+// additional code
+module place_in_rect(dx =20, dy=20)
+{
+  cols = ceil(sqrt($children)); 
+  rows = floor(sqrt($children)); 
+  for(i = [0:$children-1])
+	{ 
+	  T(dx*(-cols/2+(i%cols)+.5), dy*(rows/2-floor(i/cols)-.5))
+		 children(i); 
+	}
+}
+

model/Library/skew.scad

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+/* Taken from https://gist.github.com/boredzo/fde487c724a40a26fa9c?permalink_comment_id=4258747 */
+
+/* skew takes an array of six angles:
+ * x along y
+ * x along z
+ * y along x
+ * y along z
+ * z along x
+ * z along y
+ */
+module skew(dims) {
+matrix = [
+	[ 1, dims[0]/45, dims[1]/45, 0 ],
+	[ dims[2]/45, 1, dims[4]/45, 0 ],
+	[ dims[5]/45, dims[3]/45, 1, 0 ],
+	[ 0, 0, 0, 1 ]
+];
+multmatrix(matrix)
+children();
+}
+
+/* example:
+ * skew([45, 0, 0, 0, 0, 0])
+ * cube([10,10,10]);
+ */
+
+// Skews the child geometry.
+// xy: Angle towards X along Y axis.
+// xz: Angle towards X along Z axis.
+// yx: Angle towards Y along X axis.
+// yz: Angle towards Y along Z axis.
+// zx: Angle towards Z along X axis.
+// zy: Angle towards Z along Y axis.
+module skew2(xy = 0, xz = 0, yx = 0, yz = 0, zx = 0, zy = 0) {
+	matrix = [
+		[ 1, tan(xy), tan(xz), 0 ],
+		[ tan(yx), 1, tan(yz), 0 ],
+		[ tan(zx), tan(zy), 1, 0 ],
+		[ 0, 0, 0, 1 ]
+	];
+	multmatrix(matrix)
+	children();
+}

model/fourbar.scad

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+// fourbar.scad
+
+include <Library/BentSim/Bike_accessories.scad>
+include <Library/NACAAirfoils/files/Naca4.scad>
+include <Library/skew.scad>
+
+module fourbar_leg(length=1000, chord=100, long_skew=30, lat_skew=30) {
+    // upper pivot needs a complex trig transformation!
+    translate([(length * cos(long_skew) * cos(lat_skew)) - (2 * chord), 
+    length * cos(long_skew) * sin(lat_skew), 0])
+        rotate([0, 90+long_skew, 0])
+        cylinder(h=chord, r=12);
+    
+    // lower pivot: 
+    translate([0-chord, -12, (chord/2) * sin(long_skew) * sin(lat_skew)])
+        rotate([0, 90+long_skew, 0])
+        cylinder(h=chord, r=12);
+    
+    // aerofoil section
+    skew([0, long_skew, 0, 0, 0, 0])
+        rotate([lat_skew, 0, 180])
+        airfoil(h=length, L=chord);
+}
+
+
+module fourbar(length=1000, chord=100, long_skew=30, lat_skew=30, shoulder=650) {
+    translate([0, 0-(shoulder/2), 0])
+        fourbar_leg( length, chord, long_skew, lat_skew);
+    
+    translate([0, shoulder/2, 0])
+        mirror([0, 1, 0])
+        fourbar_leg(length, chord, long_skew, lat_skew);
+    }
+
+fourbar(600, 100, 30, 30, 650);