// ======================================================================
// Crowned Pulley for 2" Flat Belt (FRC)
// UNITS & EXPORT BEHAVIOR:
// - All *input parameters* marked *_IN are in INCHES. *_MM variables are in millimeters.
// - Internally, the model is built in MILLIMETERS (OpenSCAD geometry is unitless).
// - Most slicers/CAD import STL as MM. If yours assumes INCHES, enable export_in_inches.
// - The "crown" is a DEGREE-based cosine profile: edges fixed at input OD, center raised.
//
// Defaults:
//   - Edge OD: 4.000" (at belt edges)
//   - Belt width: 2.000"
//   - Crown: 0.035" (thousandths override = 35)
//   - Flanges: ON
//   - Hex: 1/2" with 0.006" radial clearance
// ======================================================================

inch = 25.4; // 1 inch = 25.4 mm

// ------------------------------
// GENERAL SIZE (INCHES)
// ------------------------------
pulley_edge_d_od_IN = 4.000;    // Edge OD (inches) — running diameter at belt edges   [0.75:0.0625:6.00]
belt_width_IN        = 2.000;    // Belt nominal width (inches)                         [0.50:0.010:3.00]
face_overhang_IN     = 0.400;    // Extra crowned span beyond belt width (inches)       [0.10:0.010:0.75]

// ------------------------------
// FLANGE OPTIONS
// ------------------------------
make_flanges         = true;     // Include flanges? (checkbox)                          [true:false]
flange_height_IN     = 0.080;    // Flange radial height (inches)                        [0.04:0.005:0.15]
flange_thickness_IN  = 0.080;    // Flange axial thickness (inches)                      [0.05:0.005:0.15]
flange_z_overlap_IN  = 0.020;    // Flange axial overlap into crowned span (inches)      [0.000:0.001:0.050]
flange_r_overlap_IN  = 0.015;    // Flange inner radius undercuts edge (inches)          [0.000:0.001:0.040]

// ------------------------------
// BORE (INCHES)
// ------------------------------
hex_across_flats_IN  = 0.500;    // 1/2" hex across flats (inches)                       [0.375:0.001:0.500]
hex_clearance_IN     = 0.006;    // Radial clearance for print fit (inches)              [0.000:0.001:0.012]

// ------------------------------
// CROWN CONTROLS (INCHES)
// ------------------------------
// Option A: Floating override (if your Customizer supports 0.001" steps)
crown_override_IN    = 0.000;    // Manual crown height at center (inches)               [0.000:0.001:0.100]
// Option B: Thousandths override (robust). 35 => 0.035"
crown_override_thou  = 35;       // Crown thousandths of an inch at center (integer)     [0:1:100]
crown_scale_debug    = 1.0;      // Visual multiplier (2.0 doubles crown) (unitless)     [0.1:0.1:5.0]

// ------------------------------
// DEBUG & EXPORT
// ------------------------------
debug_slice          = false;    // Show a thin cross-section slice?                      [false:true]
slice_thickness_IN   = 0.080;    // Slice thickness (inches)                              [0.010:0.010:0.200]
circum_res_min       = 240;      // circumferential smoothness ($fn)
crown_steps          = 240;      // axial samples for crown profile

// Export control: set true to export STL "in inches" (scaled down by 25.4 so mm tools show inch sizes)
export_in_inches     = false;    // Export STL scaled for inch-sized numbers?             [false:true]

// ------------------------------
// DERIVED (MM)
// ------------------------------
pulley_edge_d_od_MM = pulley_edge_d_od_IN * inch;
belt_width_MM       = belt_width_IN       * inch;
face_overhang_MM    = face_overhang_IN    * inch;

flange_height_MM    = flange_height_IN    * inch;
flange_thickness_MM = flange_thickness_IN * inch;
flange_z_overlap_MM = flange_z_overlap_IN * inch;
flange_r_overlap_MM = flange_r_overlap_IN * inch;

hex_af_MM           = hex_across_flats_IN * inch;
hex_clearance_MM    = hex_clearance_IN    * inch;

face_width_MM = belt_width_MM + face_overhang_MM;  // crowned span (between inner flange faces)
r_edge_MM     = pulley_edge_d_od_MM / 2;           // running radius at the edges

// Auto crown (inches) -> clamp 0.015"–0.035", then override/scale.
// For 4.000" OD, auto = min(0.035", 0.016 + 0.006*4 = 0.040") = 0.035"
crown_auto_IN         = max(0.015, min(0.035, 0.016 + 0.006 * pulley_edge_d_od_IN));
crown_from_float_IN   = (crown_override_IN > 0) ? crown_override_IN : crown_auto_IN;
crown_from_thou_IN    = (crown_override_thou > 0) ? (crown_override_thou / 1000.0) : 0.0;
crown_height_IN       = (crown_override_thou > 0) ? crown_from_thou_IN : crown_from_float_IN;
crown_height_MM       = crown_height_IN * inch * crown_scale_debug;

// Flange radii (inner slightly SMALLER than edge radius to overlap)
flange_inner_r_MM = max(0.1, r_edge_MM - flange_r_overlap_MM);
flange_outer_r_MM = flange_inner_r_MM + flange_height_MM;

// Axial Z range for crowned face
z0_MM = -face_width_MM/2;
z1_MM =  face_width_MM/2;

// Flange center positions (pulled inward for axial overlap)
z_flange_pos_MM = face_width_MM/2 + flange_thickness_MM/2 - flange_z_overlap_MM;

// Circumferential facets (target ~0.5 mm chord length)
circum_fn = max(circum_res_min, ceil(PI * pulley_edge_d_od_MM / 0.5));

// Debug slice thickness (mm)
slice_thickness_MM = slice_thickness_IN * inch;

// ------------------------------
// HELPERS (DEGREE-BASED TRIG)
// ------------------------------
// Cosine crown: edges fixed at r_edge; center at r_edge + crown_height.
// OpenSCAD uses DEGREE trig: cos(180 * (2*z/W))
function crown_r_MM(zMM) = r_edge_MM + crown_height_MM * 0.5 * (1 + cos(180 * (2*zMM/face_width_MM)));

// Across-flats → circumradius for $fn=6 hex: AF = 2*R*cos(30°) => R = AF / sqrt(3)
function hex_circum_r_MM(afMM, clrMM) = (afMM / sqrt(3)) + clrMM;

// Revolve profile [ [x=r, y=z], ... ] closed to axis (x=0)
function crown_profile_pts(n) =
    concat(
        [ for (i = [0:n])
            let(z = z0_MM + (face_width_MM * i / n))
            [ crown_r_MM(z), z ]
        ],
        [ [0, z1_MM], [0, z0_MM] ] // close along axis
    );

// ------------------------------
// GEOMETRY
// ------------------------------
module crowned_body() {
    rotate_extrude(angle=360, $fn=circum_fn)
        polygon(points = crown_profile_pts(crown_steps));
}

module flange_at(z_center_MM) {
    translate([0,0,z_center_MM])
        difference() {
            cylinder(h=flange_thickness_MM,     r=flange_outer_r_MM, center=true, $fn=circum_fn);
            cylinder(h=flange_thickness_MM+0.4, r=flange_inner_r_MM, center=true, $fn=circum_fn);
        }
}

module hex_bore() {
    cylinder(h = face_width_MM + (make_flanges ? 2*flange_thickness_MM : 0) + 10,
             r = hex_circum_r_MM(hex_af_MM, hex_clearance_MM),
             center = true,
             $fn = 6);
}

module crowned_pulley_solid() {
    if (make_flanges) {
        union() {
            crowned_body();
            flange_at(+z_flange_pos_MM);
            flange_at(-z_flange_pos_MM);
        }
    } else {
        crowned_body();
    }
}

module crowned_pulley() {
    difference() {
        crowned_pulley_solid();
        hex_bore();
    }
}

module slice_view(th_MM = 2.0) {
    // Slab normal to X to expose radius-vs-Z profile
    intersection() {
        crowned_pulley();
        rotate([0,90,0]) cube([th_MM, pulley_edge_d_od_MM + 2*inch, face_width_MM + (make_flanges ? 2*flange_thickness_MM : 0) + 12], center=true);
    }
}

// ------------------------------
// RENDER / EXPORT
// ------------------------------
module render_root() {
    if (debug_slice) {
        slice_view(th_MM = slice_thickness_MM);
    } else {
        crowned_pulley();
    }
}

// ======== DEBUG: Echo the *actual* sizes in the console ========
echo("Pulley edge OD (IN): ", pulley_edge_d_od_IN);
echo("Pulley edge OD (MM): ", pulley_edge_d_od_IN * 25.4);
echo("Face width (IN): ", belt_width_IN + face_overhang_IN);
echo("Face width (MM): ", (belt_width_IN + face_overhang_IN) * 25.4);
echo("Crown height (IN): ", crown_height_IN);

// Final export scaling: true -> scale by 1/25.4 so mm tools show inch-sized numbers
scale(export_in_inches ? [1/25.4, 1/25.4, 1/25.4] : [1,1,1]) render_root();