rocket.scad: three-part model rocket

diff --git a/rocket.scad b/rocket.scad
new file mode 100644 (file)
index 0000000..12d0378
--- /dev/null
+++ b/rocket.scad
@@ -0,0 +1,273 @@
+
+// The Estes A8-3 and C6-7 motors have diameter of 17.7 mm,
+// length 69.5 mm. The Estes Alpha launch pad has rod diameter 3.4 mm.
+
+motor_diam = 17.7 + 0.5; // add some tolerance
+motor_len  = 69.5 + 0.5;
+motor_wall = 2;
+
+segment_overlap = 15;
+
+thin_wall = 1.0; // depends on the print width
+thick_wall = 2.5*thin_wall;
+
+clip_spring_angle = 45;
+clip_spring_depth = 20;
+
+rod_diam = 4;
+
+eps = 0.01;
+infty = 1000;
+
+//----------------- MOTOR MODULE -----------------------------
+
+module fin() {
+       assign(h1 = 2*motor_len/3, // near end height
+               h2 = 20,        // far end height
+               h_off = motor_len, // height offset of the far height
+               w = 30, // distance of the far height
+               fin_w = thin_wall)
+       translate([0, -fin_w/2, -h1])
+       hull() { 
+               cube([eps, fin_w, h1]); // near end
+               translate([w, 0, h_off]) // far end
+                       cube([eps, fin_w, h2]);
+       };
+};
+
+// alternative fin layout
+module fin2() {
+       assign(h1 = motor_len/2, // near end height
+               w2 = 18,        // bottom/far end width
+               h_off = 50, // height offset of the far height
+               w = 30, // distance of the far height
+               fin_w = thin_wall)
+       translate([0, -fin_w/2, -h1])
+       hull() { 
+               cube([eps, fin_w, h1]); // near end
+               translate([w-w2, 0, h_off]) // far end
+                       cube([w2, fin_w, eps]);
+       };
+};
+
+rod_hole_height = 15;
+rod_hole_side = 1.5*(rod_diam + thin_wall);
+
+module motor_module_solid()
+{
+       // the lowest part is for joining the segments
+       cylinder(r = motor_diam/2 + thin_wall, h = segment_overlap + eps);
+
+       // conical joint between the two cylinders
+       translate([0, 0, segment_overlap - thick_wall + thin_wall])
+               cylinder(r1 = motor_diam/2 + thin_wall,
+                       r2 = motor_diam/2 + thick_wall,
+                       h = thick_wall - thin_wall + eps);
+
+       // protrusions to hold the main tube in place
+       for (a = [60, 180, 300]) {
+               rotate([0, 0, a]) {
+                       translate([motor_diam/2 - thin_wall, 0, 0])
+                               cylinder(r1 = thick_wall-thin_wall/2, r2 = thick_wall, h = segment_overlap/3 + eps);
+                       translate([motor_diam/2 - thin_wall, 0, segment_overlap/3])
+                               cylinder(r = thick_wall, h = 2*segment_overlap/3 + eps);
+               };
+       };
+
+       // the thick cylinder above it
+       translate([0, 0, segment_overlap])
+               cylinder(r = motor_diam/2 + thick_wall,
+               h = motor_len + motor_wall - segment_overlap);
+
+       // clip spring
+       translate([0, 0, motor_len + motor_wall])
+               intersection() {
+                       translate([motor_diam/2+6, infty/2, 4])
+                       rotate([90, 0, 0])
+                               cylinder(r = 8, h = infty);
+                       cylinder(r = motor_diam/2 + thick_wall, h = infty);
+                       rotate([0, 0, -clip_spring_angle/2+eps])
+                               cube(infty);
+                       rotate([0, 0, clip_spring_angle/2-eps])
+                               scale([1, -1, 1])
+                               cube([infty, infty, 8]);
+               };
+
+       // fins
+        for (a = [60, 180, 300]) {
+                rotate([0, 0, a])
+                translate([motor_diam/2 + thick_wall-thin_wall, 0, motor_wall + motor_len])
+                        // fin();
+                        fin2();
+        };
+
+       // rod hole holder
+       hull() {
+               translate([motor_diam/2 + thick_wall - rod_diam/2 - thin_wall,
+                       0, segment_overlap])
+                       scale([1, 1.4, 1])
+                       cylinder(r = rod_diam/2 + thin_wall, h = eps);
+               translate([motor_diam/2 + thick_wall + rod_diam/2, 0, segment_overlap + rod_hole_side])
+                       scale([1, 1.1, 1])
+                       cylinder(r = rod_diam/2 + thin_wall, h = rod_hole_height);
+               translate([motor_diam/2 + thick_wall - rod_diam/2 - thin_wall,
+                       0, segment_overlap + 2*rod_hole_side + rod_hole_height])
+                       scale([1, 1.4, 1])
+                       cylinder(r = rod_diam/2 + thin_wall, h = eps);
+       };
+
+};
+       
+module motor_module() {
+       difference() {
+               motor_module_solid();
+
+               // top ring to hold the motor inside
+               translate([0, 0, -eps])
+                       cylinder(r = motor_diam/2 - motor_wall,
+                               h = motor_wall + 2*eps);
+
+               // motor hole
+               translate([0, 0, motor_wall - eps])
+                       cylinder(r = motor_diam/2, h = motor_len + 2*eps);
+
+               // three rails inside the motor hole
+               translate([0, 0, segment_overlap + thick_wall]) difference() {
+                       union() {
+                               cylinder(r = motor_diam/2 + thin_wall,
+                                       h = motor_len - segment_overlap - 2*thick_wall + eps);
+                               translate([0, 0, motor_len - segment_overlap - 2*thick_wall])
+                                       cylinder(r1 = motor_diam/2 + thin_wall, r2 = motor_diam/2, h = thick_wall + eps);
+                       };
+                       for (a = [60, 180, 300]) rotate([0, 0, a])
+                               translate([motor_diam/2 + 2.5, 0, -eps])
+                                       cylinder(r = 3, h = infty);
+               };
+
+               // clip spring
+               for (r = [-clip_spring_angle/2, clip_spring_angle/2]) {
+                       rotate([0, 0, r])
+                       translate([-thin_wall/2, 0, motor_len + motor_wall - clip_spring_depth])
+                               cube([infty, thin_wall, infty]);
+               };
+               translate([0, 0, motor_len - eps])
+               intersection() {
+                       cylinder(r = motor_diam/2 + thin_wall,
+                               h = thick_wall + 2*eps);
+                       rotate([0, 0, -clip_spring_angle/2+eps])
+                               cube(infty);
+                       rotate([0, 0, clip_spring_angle/2-eps])
+                               scale([1, -1, 1])
+                               cube([infty, infty, 8]);
+               };
+               
+
+               // rod hole
+               translate([motor_diam/2 + thick_wall + eps + rod_diam/2, 0, 0])
+                       cylinder(r = rod_diam/2, h = infty);
+       };
+};
+
+// -------------------- CENTRAL TUBE ---------------------
+
+central_tube_h = 80;
+
+module central_tube_solid() {
+       cylinder(r = motor_diam/2 + thick_wall, h = central_tube_h);
+};
+
+module central_tube() {
+       difference() {
+               central_tube_solid();
+               translate([0, 0, -eps])
+                       cylinder(r = motor_diam/2 + thick_wall - thin_wall,
+                               h = infty);
+       };
+};
+
+//------------------------- FRONT CONE -----------------------
+cone_h = 45;
+cone_resolution = 40;
+
+function bez_i4(t, ctls) =
+       (pow(1-t, 3) * ctls[0])
+       + (3 * t * pow(1-t, 2) * ctls[1])
+       + (3 * pow(t, 2) * (1-t) * ctls[2])
+       + (pow(t, 3) * ctls[3]);
+
+module bezier_cone(cps, res)
+{
+       for (t = [0:1:res])
+               translate([0, 0, (bez_i4(t/res, cps))[0]])
+                       cylinder(r1 = (bez_i4(t/res, cps))[1],
+                               r2 = (bez_i4((t + 1)/res, cps))[1],
+                               h = (bez_i4((t + 1)/res, cps))[0]
+                                   - (bez_i4(t/res, cps))[0] + eps);
+};
+
+module front_cone_body() {
+       translate([0, 0, segment_overlap])
+               bezier_cone([
+                       [ 0, motor_diam/2 + thick_wall ], // start
+                       [ cone_h/2, motor_diam/2 + thick_wall ], // cp 1
+                       [ cone_h - motor_diam/2 - thick_wall, motor_diam/2 + thick_wall ], // cp 2
+                       [ cone_h, 0 ],
+               ], 40);
+
+       translate([0, 0, segment_overlap-thick_wall+thin_wall])
+               cylinder(r1 = motor_diam/2+thin_wall,
+                       r2 = motor_diam/2 + thick_wall,
+                       h = thick_wall - thin_wall + eps);
+
+       cylinder(r = motor_diam/2+thin_wall, h = segment_overlap + eps);
+};
+
+module front_cone() {
+       difference() {
+               front_cone_body();
+               translate([0, 0, segment_overlap])
+                       bezier_cone([
+                               [ 0.7*thin_wall, motor_diam/2 + thick_wall - thin_wall ], // start
+                       [ cone_h/2-0.7*thin_wall, motor_diam/2 + thick_wall - thin_wall], // cp 1
+                       [ cone_h - motor_diam/2 - thick_wall + thin_wall - 1.4*thin_wall, motor_diam/2 + thick_wall - thin_wall ], // cp 2
+                       [ cone_h - 1.4*thin_wall, 0 ],
+               ], 40);
+
+               translate([0, 0, segment_overlap-thick_wall+1.7*thin_wall])
+                       cylinder(r1 = motor_diam/2,
+                               r2 = motor_diam/2 + thick_wall-thin_wall,
+                               h = thick_wall-thin_wall + eps);
+
+               translate([0, 0, -eps])
+                       cylinder(r = motor_diam/2, h = segment_overlap + 2*eps);
+
+               // debug
+               // translate([0, 0, -eps]) cube(infty);
+       };
+};
+
+module thread_holder() {
+       rotate([0, 90, 0]) {
+               translate([0, 0, -1.5]) difference() {
+                       cylinder(r = 10, h = 3);
+                       translate([0, 0, -eps])
+                               cylinder(r = 8, h = 3 + 2*eps);
+               };
+       };
+}
+
+// thread_holder();
+
+$fn = 128;
+
+translate([motor_diam + thick_wall, 0, 0])
+       motor_module();
+
+rotate([0, 0, 120])
+translate([motor_diam + thick_wall, 0, 0])
+       central_tube();
+
+rotate([0, 0, 240])
+translate([motor_diam + thick_wall, 0, 0])
+       front_cone();
+