Tiny whoop case with sprung charger bay and 1S battery clips

// Tiny whoop case: the whoop, its charger and a row of 1S batteries in one hinged box.
// Printed in PETG. Seen from the front with the lid open behind, the whoop sits on
// the left in a locating ring and the charger on the right, pressed into the front
// right corner by two springs, with a window in the front wall for its charging
// cable. The lid holds the batteries standing on their side in snap clips. Two pin
// hinges with an M3 bolt each at the rear, a snap latch at the front. Every part
// prints without supports.
//
// Coordinates: y = 0 at the rear (hinges), y = Sy at the front (latch). Seen from
// the front, the viewer's right is low x: the charger corner is at low x, high y.
// The lid is modelled closed and flipped for printing.

/* [Part] */
// The whole case with the lid open, or one part in print orientation.
part = "assembly"; // [assembly, base, lid]
// Print a coupon set instead: one hinge and the latch in base and lid halves, one
// charger spring and one battery clip. Checks every fit in about an hour.
test_print = false;
// Show the whoop, the charger and the batteries as ghosts in the assembly.
show_contents = false;

/* [Whoop] */
// Motor to motor across the diagonal. A 75 mm class whoop is about 80.
whoop_wheelbase = 80; // [60:0.5:120]
// Outer diameter of one duct.
duct_d = 50; // [30:0.5:70]
// Total height of the whoop, camera included.
whoop_h = 40; // [20:1:60]

/* [Charger] */
// Charger footprint, port end against the front wall. The springs take a charger
// from 1.5 mm smaller to about 3.5 mm larger, in both directions.
charger_l = 90; // [40:1:140]
charger_w = 45; // [20:1:80]
// Height of the charger: the springs catch over its top edge.
charger_h = 20; // [8:1:40]
// Charging window in the front wall: offset of its centre from the middle of the
// charger toward the whoop, and height of its centre above the floor.
port_x = 0; // [-30:0.5:30]
port_z = 8; // [3:0.5:30]

/* [Batteries] */
// 1S batteries in the lid, standing on their side. 0 for an empty lid.
battery_count = 8; // [0:1:12]
// Length with the plug, width (its height as it stands) and thickness.
battery_l = 62; // [40:1:80]
battery_w = 13.5; // [8:0.5:20]
battery_t = 9; // [5:0.5:14]

/* [Colour] */
// Display only, the STL carries no colour.
color_case = "SteelBlue"; // [SteelBlue, White, DimGray, Black, FireBrick, Goldenrod, ForestGreen, MediumPurple]

/* [Hidden] */
$fn = 48;
wall = 2.6;
floor_t = 2;
top_t = 2;
corner_r = 4;
// whoop locating ring
w_clr = 1;
ring_t = 1.2;
ring_h = 3;
// lip on the base rim, recess in the lid
lip_h = 2;
lip_t = 1.2;
lip_c = 0.25;
// charger springs: leaf thickness, travel room behind it, preload into the charger,
// pad depth from the leaf face, pad width, slot clearance
s_t = 1.6;
travel = 5;
preload = 1.5;
pad_d = 3;
pad_w = 6;
slot_c = 0.6;
// battery clips
bat_clr = 0.25;
arm_t = 1.4;
arm_w = 6;
arm_gap = 1.6;
bump = 0.7;
// hinges: knuckle radius, axis behind the rear face, segment width and gap
bolt_d = 3.4;
rk = 4;
hk = rk + 0.5;
seg_w = 8;
seg_gap = 0.4;
hinge_in = 22;
// latch
latch_w = 20;
latch_drop = 8;
tongue_t = 1.6;
ridge_d = 1;
latch_gap = 0.3;

sq = whoop_wheelbase / sqrt(2);
whoop_span = sq + duct_d;
drone_need = whoop_span + 2 * (w_clr + ring_t) + 2;
spring_room = (pad_d - preload) + s_t + travel + slot_c + 2;
left_need = charger_w + spring_room;
bat_pitch = battery_t + 2 * (bat_clr + arm_t) + arm_gap;
Sx_in = max(left_need + drone_need, battery_count * bat_pitch + 8);
Sy_in = max(drone_need, charger_l + spring_room, battery_l + 12);
Sx = Sx_in + 2 * wall;
Sy = Sy_in + 2 * wall;
fz = floor_t;
cav_h = max(whoop_h + 2, charger_h + 6);
base_h = floor_t + cav_h;
zc = base_h;
lid_cav = max(battery_w + 2.5, 9);
lid_h = top_t + lid_cav;
pb = zc + lid_h - top_t;
// charger: outer side against the wall at low x, front face against the front wall
xi = wall + charger_w;
yf = Sy - wall;
yr = yf - charger_l;
// spring along the rear face (from the side wall) and along the inner side (from
// the front wall); free lengths
la = min(0.6 * charger_w + 3, charger_w - 2);
lb = min(max(25, 0.55 * charger_l), charger_l - 6);
// underside of the catch lip on the spring pads
zl0 = fz + charger_h + 0.2;
// whoop centre, in the zone right of the charger springs
dx = wall + left_need + (Sx_in - left_need) / 2;
dy = Sy / 2;
// latch ridge
zr = zc - latch_drop + 2.4;

// ---- 2D helpers ----

module outer2d() {
  offset(r = corner_r) offset(delta = -corner_r) square([Sx, Sy]);
}

module inset2d(k) {
  offset(r = -k) outer2d();
}

module ring2d(a, b) {
  difference() { inset2d(a); inset2d(b); }
}

// Horizontal hole that prints without support: the tip points up in 2D y.
module teardrop2d(r) {
  circle(r = r);
  rotate(45) square(r);
}

module whoop2d() {
  for (sx = [-1, 1], sy = [-1, 1]) translate([sx * sq / 2, sy * sq / 2]) circle(d = duct_d);
  square(sq, center = true);
}

// ---- Hinge ----
// Knuckle profile in (y, z) about the hinge axis, which sits hk behind the rear face
// at rim height. Its underside runs into the wall at 45 degrees. The lid mirrors it
// about the rim, so both halves print without support.

module knuckle_profile() {
  difference() {
    hull() {
      translate([-hk, 0]) circle(r = rk);
      translate([-0.01, -hk - 1.42 * rk]) square([1, hk + 1.42 * rk - 2]);
    }
    translate([-hk, 0]) teardrop2d(bolt_d / 2);
  }
}

module knuckle2d(upper) {
  translate([0, zc]) {
    if (upper) mirror([0, 1]) knuckle_profile();
    else knuckle_profile();
  }
}

// Two hinges, each base-lid-base on one M3 x 30 bolt with a nut.
module knuckles(upper) {
  for (gx = [hinge_in, Sx - hinge_in], k = upper ? [0] : [-1, 1])
    translate([gx + k * (seg_w + seg_gap) - seg_w / 2, 0, 0])
      rotate([90, 0, 90]) linear_extrude(seg_w) knuckle2d(upper);
}

// ---- Base ----

module base_shell() {
  difference() {
    union() {
      hull() {
        linear_extrude(0.01) inset2d(0.5);
        translate([0, 0, 0.5]) linear_extrude(base_h - 0.5) outer2d();
      }
      // lip on the inner half of the rim, it locates the lid
      translate([0, 0, base_h - 0.01]) linear_extrude(lip_h + 0.01) ring2d(wall - lip_t, wall);
    }
    translate([0, 0, floor_t]) linear_extrude(base_h + lip_h) inset2d(wall);
  }
}

// Low ring around the ducts and the frame: the whoop drops in and cannot slide.
module whoop_ring() {
  translate([dx, dy, fz - 0.01]) linear_extrude(ring_h + 0.01)
    difference() {
      offset(r = w_clr + ring_t) whoop2d();
      offset(r = w_clr) whoop2d();
    }
}

// Ridge on the front wall that the latch hook catches; both faces at 45 degrees.
module latch_ridge() {
  translate([Sx / 2 - (latch_w + 4) / 2, 0, 0]) rotate([90, 0, 90]) linear_extrude(latch_w + 4)
    polygon([[Sy - 0.5, zr - 1.5], [Sy + ridge_d, zr], [Sy + ridge_d, zr + 0.6], [Sy - 0.5, zr + 2.1]]);
}

// ---- Charger springs ----
// An upright leaf that hangs from a wall at its root (u = 0) and bends sideways.
// Printed upright, a sideways bend loads it along its layers. It stands on the bed
// in a slot through the floor, so it is joined to the case only at the root. The
// pad at the free end reaches preload into the charger; its top is a 45 degree ramp
// the charger edge pushes back on the way down, ending in a lip that catches over
// the charger. Local frame: u along the leaf, v toward the charger, z up.

module spring(len) {
  translate([-0.5, -s_t, 0]) cube([len + 0.5, s_t, zl0 + 2]);
  translate([len - pad_w, 0, 0]) rotate([90, 0, 90]) linear_extrude(pad_w)
    polygon([[-0.01, 0], [pad_d, 0], [pad_d, zl0], [pad_d + 1, zl0 + 1], [-0.01, zl0 + pad_d + 2.01]]);
}

module spring_slot(len) {
  translate([0, -s_t - travel - slot_c, -1])
    cube([len + slot_c, s_t + travel + slot_c + pad_d + slot_c, fz + 1.01]);
}

// Where the two springs sit: one along the rear face of the charger, hanging from
// the side wall and pushing it forward; one along its inner side, hanging from the
// front wall and pushing it against the side wall.
module spring_a() {
  translate([wall, yr - (pad_d - preload), 0]) children();
}

module spring_b() {
  translate([xi + (pad_d - preload), yf, 0]) mirror([1, 0, 0]) rotate(-90) children();
}

// Window for the charging cable, with a 45 degree roof instead of a flat top.
module port_cut() {
  lim = max(0, charger_w / 2 - 8);
  px = wall + charger_w / 2 + max(-lim, min(port_x, lim));
  pz = fz + min(port_z, cav_h - 12);
  translate([0, Sy + 1, 0]) rotate([90, 0, 0]) linear_extrude(wall + 2)
    translate([px, pz]) polygon([[-7, -4.5], [7, -4.5], [7, 2.5], [0, 9.5], [-7, 2.5]]);
}

module base() {
  difference() {
    union() {
      base_shell();
      knuckles(false);
      whoop_ring();
      latch_ridge();
    }
    spring_a() spring_slot(la);
    spring_b() spring_slot(lb);
    port_cut();
  }
  spring_a() spring(la);
  spring_b() spring(lb);
}

// ---- Lid ----

module lid_shell() {
  difference() {
    translate([0, 0, zc]) hull() {
      linear_extrude(lid_h - 0.5) outer2d();
      translate([0, 0, lid_h - 0.01]) linear_extrude(0.01) inset2d(0.5);
    }
    translate([0, 0, zc - 1]) linear_extrude(lid_cav + 1) inset2d(wall);
    // recess for the lip of the base
    translate([0, 0, zc - 1]) linear_extrude(lip_h + 0.3 + 1) ring2d(wall - lip_t - lip_c, wall + 0.01);
  }
}

// Snap tongue on the front. Its hook catches under the ridge of the base; the lip
// at its end is for a fingernail.
module latch_tongue() {
  yt = Sy + ridge_d + latch_gap;
  zt = zc - latch_drop - 3;
  translate([Sx / 2 - latch_w / 2, 0, 0]) rotate([90, 0, 90]) linear_extrude(latch_w) {
    translate([Sy - 0.5, zc + 4]) square([yt + tongue_t - (Sy - 0.5), lid_h - 4]);
    translate([yt, zt]) square([tongue_t, zc + 4.01 - zt]);
    polygon([[yt + 0.01, zr + 0.2], [Sy + latch_gap, zr - 0.8], [Sy + latch_gap, zr - 1.4], [yt + 0.01, zr - 2.4]]);
    polygon([[yt + tongue_t - 0.01, zt], [yt + tongue_t + 1.5, zt], [yt + tongue_t - 0.01, zt + 1.5]]);
  }
}

function bat_x(i) = Sx / 2 + (i - (battery_count - 1) / 2) * bat_pitch;

// 1S batteries stand on their side, thickness across x, plug end along y. Two pairs
// of arms per battery, each with a 45 degree bump that snaps over its free edge.
// arm_gap between neighbouring arms leaves room for an arm to give while the next
// slot is full.
module bat_clips() {
  if (battery_count > 0)
    for (i = [0 : battery_count - 1], yc = [Sy / 2 - 0.28 * battery_l, Sy / 2 + 0.28 * battery_l], s = [-1, 1]) {
      f = bat_x(i) + s * (battery_t / 2 + bat_clr);
      zb = pb - battery_w - 0.15;
      translate([0, yc + arm_w / 2, 0]) rotate([90, 0, 0]) linear_extrude(arm_w) {
        translate([s < 0 ? f - arm_t : f, pb - battery_w - 1.6]) square([arm_t, battery_w + 1.6 + 0.01]);
        polygon([[f + s * 0.01, zb], [f - s * bump, zb - bump], [f + s * 0.01, zb - 2 * bump]]);
      }
    }
}

module lid() {
  lid_shell();
  knuckles(true);
  bat_clips();
  latch_tongue();
}

module lid_print() {
  translate([0, Sy, zc + lid_h]) rotate([180, 0, 0]) lid();
}

// ---- Ghost contents ----

module ghost_whoop() {
  color("Gainsboro", 0.5) translate([dx, dy, fz]) {
    for (sx = [-1, 1], sy = [-1, 1]) translate([sx * sq / 2, sy * sq / 2, 0])
      difference() { cylinder(d = duct_d, h = 16); translate([0, 0, -1]) cylinder(d = duct_d - 2, h = 18); }
    translate([-12, -16, 0]) cube([24, 32, whoop_h]);
  }
}

module ghost_charger() {
  color("OrangeRed", 0.5) translate([wall, yr, fz]) cube([charger_w, charger_l, charger_h]);
}

module ghost_batteries() {
  if (battery_count > 0)
    color("DimGray", 0.6) for (i = [0 : battery_count - 1])
      translate([bat_x(i) - battery_t / 2, Sy / 2 - battery_l / 2, pb - battery_w]) cube([battery_t, battery_l, battery_w]);
}

// ---- Test coupons ----

module coupon(lo, hi) {
  translate(-lo) intersection() { children(); translate(lo) cube(hi - lo); }
}

module test_layout() {
  g = 42;
  // hinge, base and lid half
  coupon([hinge_in - 16, -hk - rk - 1, zc - 14], [hinge_in + 16, 6, zc + lip_h + 1]) base();
  translate([0, 22, 0]) coupon([hinge_in - 16, Sy - 6, 0], [hinge_in + 16, Sy + hk + rk + 1, lid_h + 12]) lid_print();
  // latch, base and lid half
  translate([g, 0, 0]) coupon([Sx / 2 - 16, Sy - 6, zc - 14], [Sx / 2 + 16, Sy + 5, zc + lip_h + 1]) base();
  translate([g, 22, 0]) coupon([Sx / 2 - 16, -6, 0], [Sx / 2 + 16, 6, lid_h + latch_drop + 5]) lid_print();
  // the spring on the inner side of the charger, with its floor slot and wall root
  translate([2 * g, 0, 0])
    coupon([xi - 4, yf - lb - 4, 0], [xi + (pad_d - preload) + s_t + travel + 1.5, Sy + 0.1, zl0 + pad_d + 3]) base();
  // one battery clip
  if (battery_count > 0) {
    yc = Sy / 2 - 0.28 * battery_l;
    bx = bat_x(0);
    translate([2 * g + 24, 0, 0])
      coupon([bx - bat_pitch / 2 - 1, Sy - yc - arm_w / 2 - 4, 0], [bx + bat_pitch / 2 + 1, Sy - yc + arm_w / 2 + 4, lid_h + 1]) lid_print();
  }
}

// ---- Layout ----

module assembly() {
  color(color_case) base();
  if (show_contents) { ghost_whoop(); ghost_charger(); }
  // lid swung open flat behind the base
  translate([0, -hk, zc]) rotate([180, 0, 0]) translate([0, hk, -zc]) {
    color(color_case) lid();
    if (show_contents) ghost_batteries();
  }
}

if (test_print) color(color_case) test_layout();
else if (part == "base") color(color_case) base();
else if (part == "lid") color(color_case) lid_print();
else assembly();