// =============================================================================
// Cyclone Separator Inlet Adapter
// =============================================================================
//
// Geometry:
//   * Vertical inlet: 40 mm OD, 35 mm ID
//   * 90 deg elbow (centerline radius 40 mm)
//   * Horizontal outlet: 70 mm long
//       - First 10 mm:  ID tapers 35 -> 30 mm  (converging)
//       - Last  60 mm:  ID widens  30 -> 32.1 mm (opening)
//
// Wall thickness: 2.5 mm constant (OD = ID + 5 mm everywhere)
//
// Construction:
//   Built as the difference between two swept hulls (outer envelope minus
//   inner envelope) along the 3D centerline. This guarantees a smooth bore
//   and a smooth outside that follows the internal contour.
//
// Print orientation suggestion:
//   Place the inlet opening face-down on the print bed so the entire
//   internal bore can be printed with minimal support material.
// =============================================================================

$fn = 80;

// ---------- User-tunable parameters (mm) ----------
inlet_length  = 15;     // length of the straight vertical inlet section
od_inlet      = 40;     // outer diameter at the inlet
id_inlet      = 35;     // inner diameter at the inlet and through the elbow
elbow_radius  = 40;     // centerline radius of the 90 deg elbow
outlet_length = 70;     // total length of the horizontal outlet
narrow_length = 10;     // length of the converging region (35 -> 30 mm ID)
id_narrow     = 30;     // inner diameter at the narrow point
id_outlet     = 32.1;   // inner diameter at the outlet opening
n_elbow       = 20;     // number of cross-sections along the elbow arc

// Internal diameter at a distance s past the elbow exit (0 <= s <= outlet_length).
function id_at(s) =
    s <= narrow_length
      ? id_inlet - (id_inlet - id_narrow) * s / narrow_length
      : id_narrow + (id_outlet - id_narrow) * (s - narrow_length) / (outlet_length - narrow_length);


module adapter() {
    // Coordinates where the elbow ends and the straight outlet begins.
    ex = elbow_radius;
    ez = inlet_length + elbow_radius;

    difference() {
        // =============================================================
        // Outer envelope: hull of outer cross-section discs
        // =============================================================
        hull() {
            // Vertical inlet straight section
            translate([0, 0, 0])
                cylinder(d = od_inlet, h = 1);
            translate([0, 0, inlet_length])
                cylinder(d = od_inlet, h = 1);

            // 90 deg elbow: arc in the XZ plane.
            //   start: (0, 0, inlet_length)         tangent +Z
            //   end:   (R, 0, inlet_length + R)    tangent +X
            for (i = [0 : n_elbow]) {
                theta = 180 - i * 90 / n_elbow;
                x_pos = elbow_radius + elbow_radius * cos(theta);
                z_pos = inlet_length + elbow_radius * sin(theta);
                // Tangent direction at angle theta: (sin(theta), 0, -cos(theta)).
                // Rotation around Y by (180 - theta) maps +Z to that tangent.
                translate([x_pos, 0, z_pos])
                rotate([0, 180 - theta, 0])
                    cylinder(d = od_inlet, h = 1);
            }

            // Horizontal outlet cross-sections (s = distance from elbow exit).
            //   OD(s) = ID(s) + 5 mm  (constant 2.5 mm wall).
            for (s = [0, 5, 10, 40, 70]) {
                translate([ex + s, 0, ez])
                    cylinder(d = id_at(s) + 5, h = 1);
            }
        }

        // =============================================================
        // Inner envelope: hull of inner cross-section discs.
        // Subtracted from the outer envelope to create the bore.
        // =============================================================
        hull() {
            translate([0, 0, 0])
                cylinder(d = id_inlet, h = 1);
            translate([0, 0, inlet_length])
                cylinder(d = id_inlet, h = 1);

            for (i = [0 : n_elbow]) {
                theta = 180 - i * 90 / n_elbow;
                x_pos = elbow_radius + elbow_radius * cos(theta);
                z_pos = inlet_length + elbow_radius * sin(theta);
                translate([x_pos, 0, z_pos])
                rotate([0, 180 - theta, 0])
                    cylinder(d = id_inlet, h = 1);
            }

            for (s = [0, 5, 10, 40, 70]) {
                translate([ex + s, 0, ez])
                    cylinder(d = id_at(s), h = 1);
            }
        }
    }
}

adapter();