From 98bbc039884f5593654c3fc5b7e829d1b395621b Mon Sep 17 00:00:00 2001
From: Justin Lin <justin.sdk@gmail.com>
Date: Wed, 24 Mar 2021 10:51:42 +0800
Subject: [PATCH] add spiral_plate

---
 examples/spiral_polygons/spiral_plate.scad | 49 ++++++++++++++++++++++
 1 file changed, 49 insertions(+)
 create mode 100644 examples/spiral_polygons/spiral_plate.scad

diff --git a/examples/spiral_polygons/spiral_plate.scad b/examples/spiral_polygons/spiral_plate.scad
new file mode 100644
index 00000000..a742b4ee
--- /dev/null
+++ b/examples/spiral_polygons/spiral_plate.scad
@@ -0,0 +1,49 @@
+use <ellipse_extrude.scad>;
+use <util/sum.scad>;
+
+beginning_radius = 15;
+fn = 5;
+number_of_polygons = 10;
+layer_height = 1.5;
+
+spiral_plate(beginning_radius, fn, number_of_polygons, layer_height);
+
+module spiral_plate(beginning_radius, fn, n, layer_height) {
+    theta = 180 / fn;
+	
+	y = beginning_radius - beginning_radius * cos(theta);
+	dr = y / cos(theta);
+	pw = pow((beginning_radius + dr) * sin(theta), 2);
+	
+	function a(ri, ro, i) = acos((pow(ro, 2) + pow(ri, 2) - pw * pow(0.985, i)) / (2 * ro * ri));
+	
+	module drawPolygon(r) {
+		circle(r, $fn = fn);
+	}
+	
+	rs = [for(i = [0: n - 1]) beginning_radius + i * dr];
+	as = [for(i = [1: n - 1]) a(rs[i - 1], rs[i], i) / 2];
+	
+	difference() {
+	    h = layer_height * (n + 1);
+		
+	    translate([0, 0, h])
+		rotate(sum([for(j = [0:n - 2]) as[j]]))
+		mirror([0, 0, 1])
+		ellipse_extrude(layer_height * (n + 5), h)
+			drawPolygon(rs[n - 1] + y);	
+			
+		translate([0, 0, layer_height * 1.01]) {
+			rotate(-as[0])
+			linear_extrude(layer_height)
+				drawPolygon(beginning_radius);
+
+			for(i = [1:n - 1]) {
+				translate([0, 0, layer_height * i])
+				rotate(sum([for(j = [0:i - 1]) as[j]]))
+				linear_extrude(layer_height)
+					drawPolygon(rs[i]);	
+			}
+		}
+	}
+}
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