add cargo bed, replace frame stub with board implementation

1 files changed, 37 insertions, 6 deletions

diff --git a/lasttretrad.scad b/lasttretrad.scad
index 6c9e2d8..f0dd6a0 100644
--- a/lasttretrad.scad
+++ b/lasttretrad.scad
@@ -1,16 +1,46 @@
 use <wheel.scad>;
 
+// total outer dimension of the lasttretrad
+ltr_length = 3000;
+ltr_width  = 1000;
+ltr_height = 160;
+
+bed_height = 18;
+
 module frame() {
-    l=3000;
-    w=1000;
-    h=160;
-    translate([-l/2, -w/2, 0])
-    cube([l, w, h]);
+    board_width=25;
+    board_height=120;
+    bessel=sqrt(3/2) -1;
+    
+    // translate([-l/2, -w/2, 0])
+    // cube([l, w, h]);
+    translate([0, 0, -board_height - bed_height]) {
+	// front/back boards
+	for (pos = [-0.9, -0.4, 0, 0.4, 0.9])
+	translate([pos * (ltr_length - board_width)/2 - board_width + board_width/2, -ltr_width/2, 0])
+	cube([board_width, ltr_width, board_height]);
+
+	// left/right boards
+	
+	//   Positioned at the bessel points (yields minimal mean bend
+	//   assuming equal load on the cargo bed); see
+	//   https://de.wikipedia.org/wiki/Bessel-Punkt
+	for (pos = [-1,1])
+	translate([-ltr_length/2, pos * (1 - 2*bessel) * (ltr_width - board_width)/2 - board_width/2, 0])
+	cube([ltr_length, board_width, board_height]);
+    }
 }
 
+// use a large plywood board
+module cargo_bed() {
+    translate([0, 0, -bed_height/2])
+    cube([ltr_length, ltr_width, bed_height], center=true);
+}
+
+
 // specify (f)ront/(c)enter/(b)ack as -1/0/1 and (l)eft/(r)ight as -1/1
 module wheel_position(fcb, lr) {
-    translate([1300 * fcb, 450 * lr, -250])
+    translate([1300 * fcb, 450 * lr, -350])
     children();
 }
 
@@ -28,6 +58,7 @@ module powered_wheel(lr=-1) {
 
 module lasttretrad() {
     frame();
+    cargo_bed();
     
     for (lr = [-1,1])
     for (fb = [-1,1])