Alwyn pointed me at his Lego wheel, so many thanks for that, I don't have one here yet to take measurements from. I rejigged the Openscad code so that I have a base to work from to design a Quad truck wheel. So this is my new starting point. Same wheel (but with 4 spokes) and less code.
hub();
//**************************
module hub () {
$fn=100;
difference(){
difference (){
union () {
translate ([0,0,-3])cylinder(18,17,17);
translate ([0,0,-3])cylinder(1.5,19,19);
translate ([0,0,13.5])cylinder(1.5,19,19);
translate ([0,0,0])cylinder(1.5,21.5,21.5);
translate ([0,0,10.5])cylinder(1.5,21.5,21.15);
}
translate ([0,0,-6])cylinder(15,15.5,15.5);
translate ([0,0,11])cylinder(5,15.5,15.5);
translate ([0,0,0])cylinder(16,1.3,1.3);
}
}
difference(){
union(){
translate ([0,0,10.5])cylinder(2,10,9);
translate ([0,0,-3.5])cylinder(19,4,4);
translate([0,0,6])rotate ([0,0,0]) cube ([32,2,8],center=true);
translate([0,0,6])rotate ([0,0,90]) cube ([32,2,8],center=true);
}
translate([0,0,-4.9])rotate([0,0,30])cylinder(30,3.5,3.5,$fn=6,center=true);
translate ([0,0,0])cylinder(16,1.3,1.3);
translate ([0,0,11])cylinder(16,2.7,2.7);
}
}