+ hull() {
+ cylinder(r = wheel_d/2, h = wheel_h, $fn = 128);
+ translate([0, 0, wheel_h/2-eps])
+ cylinder(r = wheel_d1/2, h = 2*eps, $fn = 128);
+ }
+ translate([0,0,min_wall-eps])
+ cylinder(r1 = wheel_d/2 - wheel_thick_inner,
+ r2 = wheel_d/2 - wheel_thick_outer,
+ h = wheel_h - min_wall+ 2*eps);