add spiral_polygon_fidget

examples/spiral_polygons/spiral_polygon_fidget.scad

@@ -0,0 +1,54 @@
+use <ellipse_extrude.scad>;
+use <util/sum.scad>;
+
+beginning_radius = 7.5;
+fn = 5;
+number_of_polygons = 10;
+height = 30;
+thickness = 1.5;
+
+spiral_plate(beginning_radius, fn, number_of_polygons, height);
+
+module spiral_plate(beginning_radius, fn, n, height) {
+    theta = 180 / fn;
+	
+	y = beginning_radius - beginning_radius * cos(theta);
+	dr = y / cos(theta) + thickness * 1.5;
+	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]) beginning_radius + i * dr];
+	//as = [for(i = [1: n]) a(rs[i - 1], rs[i], i) / 2];
+
+	s = [for(i = [1: n]) (rs[i] * 1.2) / rs[i - 1]];
+	
+	half_height = height / 2;
+	
+	module half() {
+	    translate([0, 0, -half_height]) {
+			linear_extrude(half_height, scale = s[0])
+			difference() {
+				drawPolygon(beginning_radius);
+				drawPolygon(beginning_radius - thickness);
+			}
+				
+			for(i = [1:n - 1]) {
+				//rotate(as[i] * 2)
+				linear_extrude(half_height, scale = s[i])
+				difference() {
+					drawPolygon(rs[i]);
+					drawPolygon(rs[i] - thickness);
+				}					
+			}
+		}
+	}
+	
+	half();	
+	mirror([0, 0, 1])
+	    half();
+}