Initial import

diff --git a/OpenSCAD-Tetramag_spheres_holder.scad b/OpenSCAD-Tetramag_spheres_holder.scad
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+/*
+ * Draw a support to tie Tetramag spheres to a bike wheel.
+ * 
+ * Copyright (C) 2018  Antonio Ospite <ao2@ao2.it>
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * Using a formula from:
+ * https://math.stackexchange.com/questions/12166/numbers-of-circles-around-a-circle
+ */
+
+function calc_inner_radius(sphere_radius, number_of_spheres) = (
+    let(ratio = sin(180 / number_of_spheres) / (1 - sin(180 / number_of_spheres)))
+    sphere_radius / ratio
+);
+
+module draw_spheres(sphere_radius, number_of_spheres) {
+     if (sphere_radius <= 0) {
+        echo("Radius of outer spheres cannot be zero");
+     }
+
+    if (number_of_spheres < 3) {
+        echo("Number of outer spheres cannot be smaller than 3");
+    }
+
+    inner_radius = calc_inner_radius(sphere_radius, number_of_spheres);
+    
+    for (i = [0:number_of_spheres]) {
+        theta = i * 360 / number_of_spheres;
+       
+       /* 
+        cx = sin(theta) * (inner_radius + sphere_radius); 
+        cy = cos(theta) * (inner_radius + sphere_radius);
+        translate([cx, cy, 0]) {
+            sphere(sphere_radius, $fn=2);
+        }
+        */
+       
+        /* A better version which also rotates the objects radially. */
+        rotate ([0, 0, theta]) {
+            translate([0, inner_radius + sphere_radius, 0]) {
+                sphere(sphere_radius, $fn=40);
+            }
+        }
+    }
+}
+
+module draw_cylinder(sphere_radius, number_of_spheres) {
+    radius = calc_inner_radius(sphere_radius, number_of_spheres) + sphere_radius / 2;
+    cylinder(sphere_radius * 2, r = radius, center=true, $fn=100);
+}
+
+module draw_mounting_holes(hole_radius) {
+    /* 9 is the number of the bike spokes to attach the holder to. */
+    mounting_holes = 9;
+    cube_size = 2;
+    cube_spacing = 2;
+    
+    for (i = [0:mounting_holes]) {
+        theta = i * 360 / mounting_holes;
+        rotate ([0, 0, theta]) {
+            translate([-cube_spacing, hole_radius + cube_size, 0]) {
+                cube([cube_size, cube_size, cube_size * 10], true);
+            }translate([cube_spacing, hole_radius + cube_size, 0]) {
+                cube([cube_size, cube_size, cube_size * 10], true);
+            }      
+        }
+    }
+    
+}
+
+module draw_holes(height, hole_radius) {
+    cylinder(height, r = hole_radius, center=true, $fn=100);
+    mounting_holes = 9;
+    cube_size = 2;
+    cube_spacing = 2;
+    
+    draw_mounting_holes(hole_radius);
+}
+
+/* The actual parameters */
+sphere_radius = 2.5;
+number_of_spheres = 38;
+hole_radius = 47 / 2; // 47mm is the hole diameter
+
+difference() {
+    draw_cylinder(sphere_radius, number_of_spheres);
+    draw_spheres(sphere_radius, number_of_spheres);
+    draw_holes(sphere_radius * 3, hole_radius);
+}