From 4cdce5dc0a707b5ce52ba88eef82b92ad1b3e7da Mon Sep 17 00:00:00 2001
From: Simon Brooke <simon@journeyman.cc>
Date: Thu, 4 Sep 2025 22:09:22 +0100
Subject: [PATCH] A good enough for now, working, parameterised, four bar
 linkage. Pleased!

---
 model/fourbar.scad | 69 ++++++++++++++++++++++++++++++++++------------
 1 file changed, 52 insertions(+), 17 deletions(-)

diff --git a/model/fourbar.scad b/model/fourbar.scad
index a9c374b..4cd7e7e 100644
--- a/model/fourbar.scad
+++ b/model/fourbar.scad
@@ -5,31 +5,66 @@ 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);
+    h = length * cos(lat_skew) * cos( long_skew);
+    w = length * sin( lat_skew);
+    d = length * sin( long_skew);
     
-    // 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);
+    translate([0, 0-w, 0]) {
+        // upper pivot needs a complex trig transformation!
+        translate([d - (chord/2), w, h + chord])
+            rotate([0, 90+long_skew, 0])
+            color("black")
+            cylinder(h=chord, r=12);
+        
+        // lower pivot: 
+        translate([0 - chord, 0, (chord/2 * sin(long_skew))])
+            rotate([0, 90+long_skew, 0])
+            color("black")
+            cylinder(h=chord, r=12);
+        
+        // aerofoil section
+        skew([0, long_skew, 0, 0, 0, 0])
+            rotate([lat_skew, 0, 180])
+            color("black")
+            airfoil(h=length, L=chord);
+     }
 }
 
 
+module fourbar_axle_half( length, chord) {
+    translate([0, 0, -120])
+        rotate([82, 0, 180])
+        color("black")
+        airfoil(h=length, L=chord);
+    
+    // lower knuckle
+    translate([-chord, length, -60])
+        color("black")
+        cube([chord, chord/4, chord/2]);
+       
+    // wheel
+    translate([0, length + 50, -50])
+        // Pierre Rouzeau's wheel is beautifully modelled and parameterised, but it doesn't seem to be scaled as I'd expect...
+        wheel(rim=451, spoke_nbr=32);
+}
+
+
+
 module fourbar(length=1000, chord=100, long_skew=30, lat_skew=30, shoulder=650) {
+    w = (length * sin( lat_skew)) + ( shoulder / 2);
+
+    
     translate([0, 0-(shoulder/2), 0])
         fourbar_leg( length, chord, long_skew, lat_skew);
     
-    translate([0, shoulder/2, 0])
+    translate([0, (shoulder/2), 0])
         mirror([0, 1, 0])
         fourbar_leg(length, chord, long_skew, lat_skew);
-    }
+    
+    fourbar_axle_half(w, chord);
+    
+    mirror([0, 1, 0])
+        fourbar_axle_half(w, chord);
+}
 
-fourbar(600, 100, 30, 30, 650);
+fourbar(700, 100, 30, 35, 650);