Wider minor-radii of PCO-1881 threads

.gitignore

@@ -0,0 +1,5 @@
+build/*.stl
+.DS_Store
+.vscode
+*.stl
+*.psd

LICENSE

@@ -0,0 +1,25 @@
+BSD 2-Clause License
+
+Copyright (c) 2019, Adrian Schlatter
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1. Redistributions of source code must retain the above copyright notice, this
+   list of conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice,
+   this list of conditions and the following disclaimer in the documentation
+   and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Makefile

@@ -0,0 +1,15 @@
+.PHONY: all
+all: imgs build
+
+.PHONY: imgs
+imgs:
+	@$(MAKE) -C docs/imgs
+
+.PHONY: build
+build:
+	@$(MAKE) -C build
+
+.PHONY: clean
+clean:
+	@$(MAKE) -C docs/imgs clean
+	@$(MAKE) -C build clean

PN1_3_narrow_fins.scad

@@ -0,0 +1,10 @@
+use <rocket_fins.scad>
+
+
+module 3_narrow_fins() {
+    rocket_fins(nfins=3, Hcenter=40, Htip=20, shift=24,
+                clearance_r=32, clearance_z=-6);
+};
+
+
+3_narrow_fins();

PN2_3_broad_fins.scad

@@ -0,0 +1,10 @@
+use <rocket_fins.scad>
+
+
+module 3_broad_fins() {
+    rocket_fins(nfins=3, Hcenter=60, Htip=30, shift=19,
+                clearance_r=50, clearance_z=-20);
+};
+
+
+3_broad_fins();

PN3_5_narrow_fins.scad

@@ -0,0 +1,10 @@
+use <rocket_fins.scad>
+
+
+module 5_narrow_fins() {
+    rocket_fins(nfins=5, Hcenter=40, Htip=20, shift=24,
+                clearance_r=32, clearance_z=-6);
+};
+
+
+5_narrow_fins();

bottle.scad

@@ -0,0 +1,31 @@
+/*
+A PET-Bottle
+
+:author: Adrian Schlatter
+*/
+
+use <pco-1881.scad>
+
+
+module bottle () {
+    profile = [[0, 0],
+               [26.19/2, 0],
+               [46, 70],
+               [46, 254],
+               [0, 254]];
+
+    translate([0, 0, 20])
+        union() {
+            rotate_extrude()
+                polygon(points=profile);
+
+            translate([0, 0, 254])
+                sphere(r=46);
+
+            translate([0, 0, -20])
+                pco1881();
+        };
+};
+
+
+bottle();

build/Makefile

@@ -0,0 +1,14 @@
+os = /usr/local/bin/openscad
+opts =
+stls = PN1_3_narrow_fins.stl PN2_3_broad_fins.stl PN3_5_narrow_fins.stl
+
+.PHONY: all
+all: $(stls)
+
+%.stl: ../%.scad
+	$(os) $(opts) -o $@ $<
+
+
+.PHONY: clean
+clean:
+	-rm $(stls) 2> /dev/null || true

docs/README.md

@@ -0,0 +1,49 @@
+# Fins for PET-Bottle Water-Rockets
+
+<p align="middle">
+<img alt="Image strip showing finned Coke-bottle water-rocket launch" src="imgs/rocket_launch.jpg" width="100%">
+</p>
+
+PET-bottle water rockets are fun. And if you have children, you already have
+an engineering-, launch-, and recovery team. Let an adult take responsibility
+for [safety](http://www.aircommandrockets.com/safety.htm): Exploding
+pressure tanks (i.e., water rockets) are dangerous!
+To learn more about water rockets, check out the excellent articles by 
+[Air Command Water Rockets](http://www.aircommandrockets.com).
+The usual way to create a very simple rocket is:
+
+- glue fins to PET bottle
+- glue nozzle to PET bottle
+- tape nose cone to PET, possibly adding some weight for stable flight
+
+Then bring your launch pad to some vast, empty area, fuel your rocket
+with water, pressurize using a bicycle pump, and launch.
+
+_Tricky part_: Glueing to PET.
+
+_Solution_: Screw-on fins that also provide
+a thread-adapter from PCO-1881 (PET-bottle thread) to 1" British
+Standard Pipe Thread (Gardena(tm) tap-connector).
+
+<p align="left">
+<img src="imgs/assembly.png" width="100%">
+</p>
+
+Note that the threads in C2 do _not_ act as seals: The lip of the bottle C1
+will directly seal to the gasket inside the tap connector C3.
+
+Some bottle-shapes may not fit into the fin-adapter. Coke bottles work nicely,
+though. It should not matter much which type of garden hose connector you use
+as long as it has a 1" British Standard Pipe Thread (often abbreviated
+as G-1"). I use [these](https://www.gardena.com/int/products/watering/hose-fittings/tap-connector-33-3-mm-g-1/967312601/).
+
+
+## Rocket-Fin Variants
+
+These variants for C2 are currently available:
+
+| Part-# | Name           | Picture                                              |
+| -------| -------------- |----------------------------------------------------- |
+|   PN1  | 3 narrow fins  | <img src="imgs/PN1_3_narrow_fins.png" height="50px"> |
+|   PN2  | 3 broad fins   | <img src="imgs/PN2_3_broad_fins.png" height="50px">  |
+|   PN3  | 5 narrow fins  | <img src="imgs/PN3_5_narrow_fins.png" height="50px"> |

docs/imgs/Makefile

@@ -0,0 +1,17 @@
+os = /usr/local/bin/openscad
+im = /usr/local/bin/magick
+opts =
+imgs = PN1_3_narrow_fins.png PN2_3_broad_fins.png PN3_5_narrow_fins.png
+
+.PHONY: all
+all: $(imgs)
+
+%.png: ../../%.scad
+	$(os) $(opts) --camera=0,0,0,52.2,0,168.5,700 --imgsize=2048,2046 \
+				  -o $@ $<
+	$(im) mogrify -transparent "rgb(255, 255, 229)" $@
+	$(im) mogrify -trim $@
+
+.PHONY: clean
+clean:
+	-rm $(imgs) 2> /dev/null || true

gardena.scad

@@ -69,7 +69,7 @@ module nozzle_gardena_G1 () {
 intersection() {
     translate([-50, 0, -50])
         color("Green")
-            cube(100, 100, 100);
+            cube(100);
     union() {
         gasket_gardena_G3o4();
         nozzle_gardena_G3o4();

pco-1881.scad

@@ -44,6 +44,6 @@ module pco1881 () {
 intersection() {
     color("Green")
         translate([-50, 0, -50])
-            cube(100, 100, 100);
+            cube(100);
     !pco1881($fn=120);
-}
+}

rocket.scad

@@ -0,0 +1,45 @@
+/*
+Water Rocket Exploded Model
++++++++++++++++++++++++++++++
+
+:author: Adrian Schlatter
+*/
+
+use <gardena.scad>
+use <bottle.scad>
+use <PN1_3_narrow_fins.scad>
+use <PN2_3_broad_fins.scad>
+use <PN3_5_narrow_fins.scad>
+
+
+  // rocket with rocket fins variant _3:
+union() {
+    // bottle:
+    translate([0, 0, 50])
+        rotate([0, 0, 3])
+            color("Silver")
+                bottle($fn=120);
+
+    // rocket fins _3:
+    color("Gold")
+        5_narrow_fins();
+
+    // nozzle:
+    translate([0, 0, -2.8 - 20]) {
+        rotate([0, 0, -65])
+            color("Gray")
+                nozzle_gardena_G1();
+        gasket_gardena_G1();
+    };
+
+};
+
+// rocket fins variant _1:
+translate([-200, 0, 0])
+    color("Gold")
+        3_narrow_fins();
+
+// rocket fins variant _2:
+translate([-200, 0, +70])
+    color("Gold")
+        3_broad_fins();

WaterRocketAdapter1.scad → rocket_fins.scad

@@ -1,5 +1,5 @@
 /*
-WaterRocketAdapter Type 1
+Rocket Fin Adapter
 ++++++++++++++++++++++++++
 
 Connects a PCO-1881-thread bottle to a Gardena G1 nozzle. The PET bottle seals 
@@ -11,15 +11,16 @@ directly on the gasket of the Gardena nozzle. Key design aspects:
 
 :author: Adrian Schlatter
 :date: 2019-04-18
-
 */
 
 use <threadlib/threadlib.scad>
 use <gardena.scad>
-use <pco-1881.scad>
+use <bottle.scad>
 use <fins.scad>
 
-module WaterRocketAdapter1($fn=120)
+
+module rocket_fins(nfins=3, Hcenter=40, Htip=20, shift=24,
+                  clearance_r=32, clearance_z=-6, $fn=120)
 {
     tol = 0.2;
     pco1881_Rmajor = thread_specs("PCO-1881-int")[2] / 2;
@@ -37,7 +38,8 @@ module WaterRocketAdapter1($fn=120)
                [Rbrim + tol, 9.5 + Hgrip], [Rbrim + tol, 15.5],
                [pco1881_Rmajor, 9.0], [pco1881_Rmajor, dH]];
     clearance = [[0, section[6][1] + 10], section[6] + [8, 10],
-                 section[7] + [0.5, 0], section[3], [50, -20], [0, -20]];
+                 section[7] + [0.5, 0], section[3], [clearance_r, clearance_z],
+                 [0, clearance_z]];
     union() {
         rotate_extrude()                                    // entire body of adapter
             offset(r=-1)
@@ -61,8 +63,8 @@ module WaterRocketAdapter1($fn=120)
             translate([0, 0, dH + 3 * P_pco / 4])
                 thread("PCO-1881-int", turns=1.95);
         difference() {                                      // fins
-            translate([0, 0, 19])
-                    fins(Hcenter=60, Htip=30, r=0.5, nfins=3);
+            translate([0, 0, shift])
+                    fins(Hcenter=Hcenter, Htip=Htip, r=0.5, nfins=nfins);
             rotate_extrude()
                 polygon(points=clearance);
         };
@@ -73,19 +75,22 @@ module WaterRocketAdapter1($fn=120)
 intersection() {
     translate([-100, 0, -100])
         color("Green")
-            cube([200, 200, 200]);
+            cube(200);
     rotate([0, 0, 0])
     union() {
-        rotate([0, 0, 3])
-        color("White")                                      // botte neck
-            pco1881($fn=120);
-        translate([0, 0, -2.8]) {                           // gardena nozzle
+        translate([0, 0, 50])
+            rotate([0, 0, 3])
+                color("Silver")                              // bottle
+                    bottle($fn=120);
+
+        color("Gold")                                  // Adapter
+            !rocket_fins();
+
+        translate([0, 0, -2.8 - 20]) {                      // gardena nozzle
             rotate([0, 0, -65])
                 color("Gray")
                     nozzle_gardena_G1();
-            *gasket_gardena_G1();                            // gasket
+            gasket_gardena_G1();                            // gasket
         };
-        color("FireBrick")                                  // Adapter
-            !WaterRocketAdapter1();
     };
-};
+};