// =====================================================================
// Coupon Test Cell Hardware  (build plan phase 2E)
// Small Zn-MnO2 test cells that match the full cell's plate thickness,
// felt compression and current per area, at 1/124 of the active area.
//
// Parts:
//   clamp_plate  - print 2 per coupon. Sets the stack gap with built-in
//                  standoffs.
//   box, lid     - small electrolyte cup with tab slots and a vent hole.
//   die_base, die_frame, die_punch, notch_shim
//                - press die that makes 30 x 30 x 2.90 mm cathode
//                  coupons with the Ti mesh tab in the middle.
// Units: mm.
// =====================================================================
//
// FILAMENT: PETG (same as the cell case; see cell_module_case.scad).
//   Box, lid, clamp plates: 4 perimeters, 100% infill, 0.2 mm layers.
//   Press die: 100% infill, 6+ perimeters. A PETG die is fine up to
//   about 1-1.5 tonnes on the punch (about 10-15 MPa on the coupon).
//   The punch stops at its shoulder, so the coupon thickness is set by
//   the die, not by the force. If the shoulder won't seat at 1.5 t, the
//   mix is too dry or overweight. For higher force, use this model as a
//   pattern for an aluminum die.
//
// ---------------------------------------------------------------------
// COUPON STACK (front to back):
//   clamp plate | Zn 0.20 | felt 0.88 | cathode 2.90 | felt 0.88 | Zn 0.20 | clamp plate
//   Gap between plates = 5.06 mm, set by standoffs (2.53 mm per plate).
//
// Coupon cathode: 30 x 30 mm, 4.87 g mix (3.65 g MnO2 + 1.22 g carbon
//   + about 0.2 g PTFE solids), with a Ti mesh 30 x 30 + tab 6 wide x 45
//   above the coupon (75 overall).
// Zinc coupons:  30 x 30 x 0.20 mm + tab 6 wide x 45 above (2 per coupon cell).
//                Tab positions: front zinc 6 mm, cathode 15 mm, back zinc
//                24 mm from the coupon's left edge (centres).
// Felt:          34 x 34 mm (2 mm overhang all round), 2 per coupon cell.
// Bolts:         4 x M4 x 20 nylon pan-head + nylon nuts.
// Test current:  28 mA (= 1.56 mA/cm2, same as 3.5 A in the full cell).
// Electrolyte:   about 45 mL to the fill-line groove (flooded; the full cell is lean, so the
//                coupon shows electrode behaviour, not electrolyte limits).
// Join the two zinc tabs together outside the cup with a short wire.
// ---------------------------------------------------------------------

part = "assembly";
// "clamp_plate", "box", "lid", "die_base", "die_frame", "die_punch",
// "notch_shim", "assembly", "print_cell" (box + lid + 2 plates),
// "print_die" (die parts laid out)

$fn = 48;
eps = 0.01;

// ---- coupon stack ----
cp      = 30;      // coupon size
zn_t    = 0.20;
felt_t  = 0.88;    // compressed
cath_t  = 2.90;
gap     = 2*zn_t + 2*felt_t + cath_t;   // 5.06
felt_sz = 34;
tab_w   = 6;
tab_len = 75;      // from coupon bottom: reaches about 20 mm above the lid

// ---- clamp plate ----
pl_w    = 50;      // X
pl_h    = 50;      // Z (height)
pl_t    = 5;       // Y
cp_x0   = (pl_w - cp)/2;   // coupon X start on the plate = 10
cp_z0   = 10;              // coupon bottom height on the plate
bolt_d  = 4.4;             // M4 clearance
bolt_in = 4.5;             // bolt centre from plate edges
pad     = 7;               // standoff pad size
stand_h = gap/2;           // 2.53 per plate

// tab X positions across the coupon (relative to coupon left edge)
tab_cath_x = 15;           // centre
tab_zf_x   = 6;            // front zinc
tab_zb_x   = 24;           // back zinc

// ---- cup ----
wall    = 2.0;
bolt_stick = 6.5;          // M4 head (3 mm) + nut (3.2) + slack, per side
in_x    = pl_w + 4;                          // 54
in_y    = pl_t*2 + gap + 2*bolt_stick;       // about 28
in_z    = 62;
floor_t = 2.0;
lid_t   = 3.0;  lip_h = 3;  lip_w = 1.2;  lip_gap = 0.2;
vent_d  = 2.5;
fill_line = cp_z0 + cp + 8;   // electrolyte level above the floor

// ---- press die ----
die_sz   = 60;
cav      = 30.2;               // cavity (coupon + 0.1 clearance per side)
base_t   = 8;
frame_h  = 14;
pin_d    = 4;  pin_h = 4;  pin_clear = 0.3;
pin_pos  = [[6, 6], [54, 54]];
punch_cl = 0.15;               // punch clearance per side
shoulder = 50;  shoulder_t = 6;
notch_h  = cath_t/2 + 0.1;     // 1.55: tab top at mid thickness
shim_h   = notch_h - 0.2;      // 1.35: sits under the 0.2 mm tab

// =====================================================================
module clamp_plate() {
    // Inner face is at y = pl_t (pads stick out toward the coupon).
    difference() {
        union() {
            cube([pl_w, pl_t, pl_h]);
            for (x = [bolt_in, pl_w - bolt_in], z = [bolt_in, pl_h - bolt_in])
                translate([x - pad/2, pl_t - eps, z - pad/2])
                    cube([pad, stand_h + eps, pad]);
        }
        for (x = [bolt_in, pl_w - bolt_in], z = [bolt_in, pl_h - bolt_in])
            translate([x, -1, z]) rotate([-90, 0, 0])
                cylinder(d = bolt_d, h = pl_t + stand_h + 2);
    }
}

module coupon_stack_ghost() {
    // visual only: zinc, felt, cathode and tabs between the plates
    y0 = pl_t;
    layers = [["zn", zn_t], ["felt", felt_t], ["cath", cath_t], ["felt", felt_t], ["zn", zn_t]];
    color("Silver") translate([cp_x0, y0, cp_z0]) cube([cp, zn_t, cp]);
    color("Khaki") translate([cp_x0 - 2, y0 + zn_t, cp_z0 - 2]) cube([felt_sz, felt_t, felt_sz]);
    color("DimGray") translate([cp_x0, y0 + zn_t + felt_t, cp_z0]) cube([cp, cath_t, cp]);
    color("Khaki") translate([cp_x0 - 2, y0 + zn_t + felt_t + cath_t, cp_z0 - 2]) cube([felt_sz, felt_t, felt_sz]);
    color("Silver") translate([cp_x0, y0 + gap - zn_t, cp_z0]) cube([cp, zn_t, cp]);
    // tabs
    color("Silver") translate([cp_x0 + tab_zf_x - tab_w/2, y0, cp_z0 + cp]) cube([tab_w, zn_t, tab_len - cp]);
    color("LightSlateGray") translate([cp_x0 + tab_cath_x - tab_w/2, y0 + gap/2 - 0.1, cp_z0 + cp]) cube([tab_w, 0.2, tab_len - cp]);
    color("Silver") translate([cp_x0 + tab_zb_x - tab_w/2, y0 + gap - zn_t, cp_z0 + cp]) cube([tab_w, zn_t, tab_len - cp]);
}

module clamp_pair() {
    // front plate, then the back plate mirrored so the pads meet
    clamp_plate();
    translate([0, 2*pl_t + gap, 0]) mirror([0, 1, 0]) clamp_plate();
}

// =====================================================================
// position of the clamp pair inside the cup (inner corner = origin)
stack_x = (in_x - pl_w)/2;
stack_y = (in_y - (2*pl_t + gap))/2;

module box() {
    difference() {
        cube([in_x + 2*wall, in_y + 2*wall, in_z + floor_t]);
        translate([wall, wall, floor_t]) cube([in_x, in_y, in_z + 1]);
        // fill line groove on the outside, 0.4 mm deep
        translate([-eps, -eps, floor_t + fill_line])
            cube([in_x + 2*wall + 2*eps, 0.4, 0.6]);
    }
    // two locating rails on the floor so the clamp pair sits centred
    for (y = [stack_y - 1.2, stack_y + 2*pl_t + gap])
        translate([wall + stack_x + 8, wall + y, floor_t - eps])
            cube([pl_w - 16, 1.2, 2 + eps]);
}

module lid() {
    // underside at z = 0
    difference() {
        union() {
            cube([in_x + 2*wall, in_y + 2*wall, lid_t]);
            translate([wall + lip_gap, wall + lip_gap, -lip_h])
                difference() {
                    cube([in_x - 2*lip_gap, in_y - 2*lip_gap, lip_h + eps]);
                    translate([lip_w, lip_w, -eps])
                        cube([in_x - 2*lip_gap - 2*lip_w, in_y - 2*lip_gap - 2*lip_w, lip_h + 3*eps]);
                }
        }
        // tab slots (tab + 1 mm each way)
        sy = wall + stack_y + pl_t;
        tab_slot(wall + stack_x + cp_x0 + tab_zf_x, sy);
        tab_slot(wall + stack_x + cp_x0 + tab_cath_x, sy + gap/2);
        tab_slot(wall + stack_x + cp_x0 + tab_zb_x, sy + gap);
        // vent hole
        translate([wall + in_x - 6, wall + in_y/2, -lip_h - 1]) cylinder(d = vent_d, h = 20);
        // labels
        translate([wall + stack_x + cp_x0 + tab_cath_x, wall + 3, lid_t - 0.6])
            linear_extrude(1) text("+", size = 4, halign = "center", valign = "center");
        translate([wall + stack_x + cp_x0 + tab_zf_x, wall + 3, lid_t - 0.6])
            linear_extrude(1) text("-", size = 4, halign = "center", valign = "center");
    }
}

module tab_slot(xc, yc) {
    translate([xc - (tab_w + 2)/2, yc - 1.2, -lip_h - 1])
        cube([tab_w + 2, 2.4, lid_t + lip_h + 2]);
}

// =====================================================================
// Press die: base with pins, removable frame, stepped punch.
// Use: frame on base -> notch shim in notch -> half the mix ->
// mesh (tab out through the notch, resting on the shim) -> rest of mix ->
// punch -> press until the shoulder seats -> remove punch -> lift the
// frame straight up -> slide the coupon off.
module die_base() {
    difference() {
        cube([die_sz, die_sz, base_t]);
    }
    for (p = pin_pos)
        translate([p[0], p[1], base_t - eps]) cylinder(d = pin_d, h = pin_h + eps);
}

module die_frame() {
    c0 = (die_sz - cav)/2;
    difference() {
        cube([die_sz, die_sz, frame_h]);
        translate([c0, c0, -1]) cube([cav, cav, frame_h + 2]);
        for (p = pin_pos)
            translate([p[0], p[1], -1]) cylinder(d = pin_d + pin_clear, h = pin_h + 1.5);
        // tab notch through the +X wall, open at the bottom
        translate([c0 + cav - 1, die_sz/2 - (tab_w + 0.6)/2, -1])
            cube([c0 + 2, tab_w + 0.6, notch_h + 1]);
        // mark the tab side
        translate([die_sz - 4, die_sz/2, frame_h - 0.6])
            linear_extrude(1) text("TAB", size = 3, halign = "center", valign = "center");
    }
}

module die_punch() {
    // Upside down for printing: shoulder on the bed, body upward.
    // Body length = frame_h - cath_t, so the punch face stops 2.90 mm
    // above the base when the shoulder sits on the frame.
    body = cav - 2*punch_cl;
    union() {
        translate([-shoulder/2, -shoulder/2, 0]) cube([shoulder, shoulder, shoulder_t]);
        translate([-body/2, -body/2, shoulder_t - eps]) cube([body, body, frame_h - cath_t + eps]);
    }
}

module notch_shim() {
    // fills the notch under the tab so powder can't escape
    c0 = (die_sz - cav)/2;
    cube([c0, tab_w + 0.4, shim_h]);   // flush with the cavity wall
}

// =====================================================================
if (part == "clamp_plate") {
    rotate([90, 0, 0]) clamp_plate();   // outer face on the bed, pads up
} else if (part == "box") {
    box();
} else if (part == "lid") {
    translate([0, 0, lip_h]) lid();
} else if (part == "die_base") {
    die_base();
} else if (part == "die_frame") {
    die_frame();
} else if (part == "die_punch") {
    die_punch();
} else if (part == "notch_shim") {
    notch_shim();
} else if (part == "print_cell") {
    box();
    translate([in_x + 2*wall + 8, 0, lip_h]) lid();
    translate([0, in_y + 2*wall + 10 + pl_h, 0]) rotate([90, 0, 0]) clamp_plate();
    translate([pl_w + 8, in_y + 2*wall + 10 + pl_h, 0]) rotate([90, 0, 0]) clamp_plate();
} else if (part == "print_die") {
    die_base();
    translate([die_sz + 8, 0, 0]) die_frame();
    translate([2*die_sz + 16 + shoulder/2, shoulder/2, 0]) die_punch();
    translate([0, die_sz + 8, 0]) notch_shim();
} else if (part == "assembly") {
    color("LightSteelBlue", 0.35) box();
    translate([wall + stack_x, wall + stack_y, floor_t]) {
        color("SteelBlue") clamp_pair();
        coupon_stack_ghost();
    }
    color("SteelBlue", 0.5) translate([0, 0, floor_t + in_z + 15]) lid();
    // die, shown beside the cup
    translate([in_x + 30, 0, 0]) {
        color("Gainsboro") die_base();
        color("LightGray") translate([0, 0, base_t]) die_frame();
        color("DarkGray") translate([die_sz/2, die_sz/2, base_t + frame_h + shoulder_t + 20])
            mirror([0, 0, 1]) die_punch();
    }
}