I had a chat with Serge, consulting with him our progress in this space and he came with some interesting ideas. But let’s recap a bit first.
This is our cylindrical vector thrust exhaust Mk I.

Also after hearing Risa calling Hairdryer I spent few hours in OpenSCAD and replaced that central cylinder with a sphere.

I am adding that code here just for reference.
use <ShortCuts.scad>
use <Naca4.scad>
//Sphere-based vector thrust exhaust
module outer_solid(dm, size, diff) {
cylinder(size+diff+10, dm-7, dm-7, center = false);
sphere(dm);
}
module outer_part() {
difference() {
union() {
difference() {
outer_solid(40, 55, 0);
outer_solid(38.5, 55, 2);
}
}
//outlet cutout
difference() {
Tz(-39)
scale([1,3,0.555])
sphere(60);
//axel clamp meat
Rx(90)Tz(39.2)
cylinder(4, 8, 8, center = true);
//axel clamp meat
Rx(90)Tz(-39.2)
cylinder(4, 8, 8, center = true);
}
//axel holes
Rx(90)Tz(39)
cylinder(2, 6.2, 6.1, center = true);
Rx(90)Tz(-39)
cylinder(2, 6.1, 6.2, center = true);
}
}
module inner_solid(dm, diff) {
//main bowl
sphere(dm);
//exhoust
Rx(180)Tz(5)
scale([0.9,1.4,1])
cylinder(65+diff/2, 27-diff/2, 20-diff/2, center = false);
}
module axel(tz, flexIn, flexOut, noSlide) {
difference() {
Rx(90)Tz(tz)
cylinder(2, flexIn, flexOut, center = true);
r = tz > 0 ? -8 : 8;
tz2 = tz > 0 ? tz+7.8 : tz-7.8;
if (noSlide) {
//servo gear hole
Rx(90)
Tz(tz-1) {
difference() {
cylinder(9, 2.6, 2.6, center = true);
n=12;
for(w=[0:360/n:359])
Rz(w)
Tx(2.7)
cylinder(9.2, 0.4, 0.4, center = true);
}
}
} else {
//slide
T(0, -tz2, 0)
Rx(r)
cube(15, center = true);
}
}
}
module inner_part() {
//inner cylinder
Rz(180)
difference() {
inner_solid(38.2, 0);
inner_solid(36.7, 2);
T(0, 0, -120)
cube(60, center = true);
//inlet cutout
Tz(31)
scale([0.62,0.6,1])
sphere(60);
//Upper Axel cutout
Rx(90)Tz(-39.5)
cylinder(4.5, 2.8, 2.8, center = true);
}
//axels
axel( 38.3, 6.1, 6, true); //upper axel
axel(-38.3, 6.1, 6, false); //bottom axel
}
I did a print in 1:2 not to loose too much of material and it worked out pretty well again.

However, Serge came with an idea that having a cone exhaust like this – forming a jet – might cost us too much on overall efficiency. So I’ve designed something else!
use <ShortCuts.scad>
use <Naca4.scad>
//Rudder-based vector thrust exhaust
module servo_gear_hole(dm) {
T(dm-1,0,dm)Ry(90) {
T(0,0,-4)
cylinder(6, 1, 5, center = true);
difference() {
cylinder(4, 10, 10, center = true);
//servo gear hole
Tz(-1) {
difference() {
cylinder(9, 2.5, 2.5, center = true);
n=12;
for(w=[0:360/n:359])
Rz(w)
Tx(2.5)
cylinder(9.2, 0.4, 0.4, center = true);
}
}
}
}
}
module bottom_axel_hole(dm) {
T(-dm+1,0,dm)Ry(270) {
T(0,0,-4)
cylinder(6, 1, 5, center = true);
cylinder(2, 10, 10, center = true);
}
}
module cone(dm, height, diff) {
//left tube
T(0,60,-height)Rx(31)
cylinder(height+18+diff, dm-diff, dm-diff, center = false);
//right tube
T(0,-60,-height)Rx(-31)
cylinder(height+18+diff, dm-diff, dm-diff, center = false);
//central part
Tz(-60)
scale([dm*2-diff*7,1.5,1.5])
R(0,270,0)
circle(dm+diff/2,$fn=3);
}
module body(dm, wall) {
height = 100;
Tz(height/2)
intersection() {
difference() {
union() {
Tz(height/2-25)
cylinder(height/2+20, dm, dm, center = true);
cone(dm, height, 0);
}
cylinder(height+wall+20, dm-wall, dm-wall, center = true);
cone(dm, height, wall);
}
//nice conic trim
scale([2,2,2])
sphere(dm);
}
}
module rudder(dm, wall) {
$fn=50;
//main plange
Tz(dm)
R(0,90,90)
minkowski() {
cube([30,1,1]);
cylinder(r=dm-wall*1.5, h=2, center=true);
}
//reinforcement 1
Ry(90)T(-dm,0,dm/3)
scale([5,1,1])
cylinder(2, 7, 7, center = true);
//reinforcement 2
Ry(90)T(-dm,0,-dm/3)
scale([5,1,1])
cylinder(2, 7, 7, center = true);
}
$fn = 100;
dm = 42;
wall = 1.5;
body(dm, wall);
servo_gear_hole(dm);
bottom_axel_hole(dm);
rudder(dm, wall);
What OpenSCAD translates into this beauty:

And then I set it to move 😉
… and now we are ready to do some new printing! 🙂
Hummm… I think with this system you loose the JET effect, you loose the trust advantage of the jet.
……………………………….. -Sent by “either” Robin or Serge. -Mail may be from; acrohc@me.com, acrohc@iCloud.com or acrohc@yahoo.com They are all valid. -Also, any bad grammar or spelling is due to self correcting!!!
>
Darn, we’ll need to plan some testing around it! Let’s print all of those in the same size, connect those to our EDF unit and get some data 🙂
Nemyslím