Tiny whoop case with clip-in zigzag springs, flush slider and latch

// Tiny whoop case: the whoop, its charger and a row of 1S batteries in one hinged box,
// printed in PETG, with a smooth outside. The base is filled up to a deck with a
// pocket shaped around the ducts of the whoop and a pocket for the charger in the
// front right corner (seen from the front with the lid open behind). Flat-printed
// zigzag springs with a T clip slide into sockets in the pocket walls: two press the
// charger into its corner, four hold a smaller whoop. A flush slider closes the
// window for the charging cable, a flush snap latch closes the lid. 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 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, slider, charger_springs, whoop_springs]
// Print a coupon set instead: one hinge and the latch in base and lid halves, the
// slider channel with the slider, a charger spring socket with its spring, and one
// battery clip.
test_print = false;
// Show the four whoop springs, and the smaller whoop as ghost, in the assembly.
show_insert = true;
// Show the whoop, the charger and the batteries as ghosts in the assembly.
show_contents = false;

/* [Whoop] */
// The whoop the pocket fits without springs. Motor to motor across the diagonal:
// 80 for a Meteor75 Pro II.
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]

/* [Whoop springs] */
// A smaller whoop held in the pocket by the four whoop springs: wheelbase and duct
// diameter.
insert_wheelbase = 65; // [50:0.5:110]
insert_duct_d = 36; // [25:0.5:65]

/* [Charger] */
// Charger size, port end against the front wall. The springs take a charger from
// 2 mm smaller to about 2 mm larger, in both directions.
charger_l = 90; // [40:1:140]
charger_w = 45; // [20:1:80]
charger_h = 20; // [8:1:40]
// Charging window: 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 = 10; // [9:0.5:30]

/* [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 = 3.2;
floor_t = 2;
top_t = 2;
corner_r = 6;
bot_ch = 1.5;
top_ch = 2;
seam_ch = 0.6;
// deck that fills the base around the pockets, clearance around the whoop, room
// between the charger and its pocket walls for the springs
deck_h = 14;
c_clr = 0.5;
c_gap = 9;
// lip on the base rim, recess in the lid
lip_h = 2;
lip_t = 1.2;
lip_c = 0.25;
// clip-in springs: height, strip, pitch, socket lip, head depth and width, neck
// width, pad thickness, preload
sp_h = 6;
sp_st = 0.8;
sp_p = 2.5;
sp_lip = 1.6;
sp_hd = 2;
sp_hw = 8;
sp_nw = 3;
sp_pad = 2;
sp_pre = 2;
sp_slot = sp_lip + sp_hd + 0.3;
// window and slider
sl_w = 30;
sl_h = 16;
sl_t = 1.6;
sl_travel = 13;
det = 0.5;
// 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 = 10;
tongue_t = 1.6;

sq = whoop_wheelbase / sqrt(2);
whoop_span = sq + duct_d;
drone_need = whoop_span + 2 * c_clr + 2.4;
charger_zone = charger_w + c_gap + sp_slot + 1.2;
bat_pitch = battery_t + 2 * (bat_clr + arm_t) + arm_gap;
Sx_in = max(charger_zone + drone_need, battery_count * bat_pitch + 8);
Sy_in = max(drone_need, charger_l + c_gap + sp_slot + 1.2, battery_l + 12);
Sx = Sx_in + 2 * wall;
Sy = Sy_in + 2 * wall;
fz = floor_t;
cav_h = max(whoop_h + 2, charger_h + 4, deck_h + 4);
base_h = fz + 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 pocket: the charger sits against the outer and the front wall
yf = Sy - wall;
cx_in = wall + charger_w + c_gap;
cy_r = yf - charger_l - c_gap;
c_len = c_gap + sp_pre;
// whoop pocket and its four spring sockets on the diagonals
dx = wall + charger_zone + (Sx_in - charger_zone) / 2;
dy = Sy / 2;
r_out = whoop_wheelbase / 2 + duct_d / 2 + c_clr;
w_len = r_out - (insert_wheelbase / 2 + insert_duct_d / 2) + sp_pre;
w_ok = w_len >= 8;
// window and slider
p_lim = max(0, charger_w / 2 - 9);
px = max(corner_r + sl_w / 2 + sl_t + 1.5, wall + charger_w / 2 + max(-p_lim, min(port_x, p_lim)));
pz = fz + max(9, min(port_z, cav_h - 22));
sl_z0 = pz - sl_h / 2;

// ---- 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);
}

// Whoop outline: four ducts on a square of side s, and the frame between them.
module whoop2d(s, d) {
  for (sx = [-1, 1], sy = [-1, 1]) translate([sx * s / 2, sy * s / 2]) circle(d = d);
  square(s, center = true);
}

// ---- Clip-in spring ----
// Printed flat. A zigzag of thin strips: each is a little wall that bends sideways,
// along its layers. A neck on the middle of the first strip carries a T head that
// drops into a socket from above; a stub on the middle of the last strip carries
// the pad, whose top front edge is chamfered so the whoop or charger pushes it back
// on the way down. Local frame: the pocket face at x = 0, the spring along +x,
// len is the relaxed length from the pocket face to the pad face.

module serp_spring(len, w, pw) {
  x0 = 1;
  avail = len - x0 - 1 - sp_pad;
  n = max(2, floor((avail - sp_st) / sp_p) + 1);
  p = (avail - sp_st) / (n - 1);
  xf = len;
  difference() {
    linear_extrude(sp_h) {
      translate([-sp_lip - sp_hd - 0.15, -sp_hw / 2]) square([sp_hd, sp_hw]);
      translate([-sp_lip - 0.16, -sp_nw / 2]) square([sp_lip + 0.16 + x0 + 0.01, sp_nw]);
      for (i = [0 : n - 1]) translate([x0 + i * p, -w / 2]) square([sp_st, w]);
      for (i = [0 : n - 2]) translate([x0 + i * p, i % 2 == 0 ? w / 2 - sp_st : -w / 2]) square([p + sp_st, sp_st]);
      translate([x0 + (n - 1) * p, -sp_nw / 2]) square([sp_st + 1.01, sp_nw]);
      translate([xf - sp_pad, -pw / 2]) square([sp_pad, pw]);
    }
    translate([0, pw / 2 + 1, 0]) rotate([90, 0, 0]) linear_extrude(pw + 2)
      polygon([[xf + 0.01, sp_h - 1.6], [xf + 0.01, sp_h + 0.01], [xf - 1.6, sp_h + 0.01]]);
  }
}

// Vertical T slot behind a pocket face, open at the top, same local frame.
module spring_socket() {
  translate([0, 0, -0.01]) linear_extrude(deck_h + 0.03) {
    translate([-sp_lip - 0.01, -(sp_nw / 2 + 0.25)]) square([sp_lip + 0.03, sp_nw + 0.5]);
    translate([-sp_slot, -(sp_hw / 2 + 0.2)]) square([sp_slot - sp_lip + 0.01, sp_hw + 0.4]);
  }
}

// Where the charger springs sit: one in the middle of the rear face of the pocket,
// pushing the charger forward, one in the middle of its inner face, pushing it
// against the outer wall.
module at_charger_springs() {
  translate([wall + charger_w / 2, cy_r, fz]) rotate(90) children();
  translate([cx_in, yf - charger_l / 2, fz]) rotate(180) children();
}

// The four whoop springs, one on each diagonal at the outer point of a duct, all
// pushing toward the centre.
module at_whoop_springs() {
  for (sx = [-1, 1], sy = [-1, 1])
    translate([dx + sx * r_out / sqrt(2), dy + sy * r_out / sqrt(2), fz]) rotate(atan2(-sy, -sx)) children();
}

// ---- 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(bot_ch);
        translate([0, 0, bot_ch]) linear_extrude(base_h - bot_ch - seam_ch) outer2d();
        translate([0, 0, base_h - 0.01]) linear_extrude(0.01) inset2d(seam_ch);
      }
      // 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);
  }
}

// The deck fills the base up to deck_h, around the whoop pocket and the charger
// pocket. Slice it with sparse infill.
module deck() {
  translate([0, 0, fz - 0.01]) linear_extrude(deck_h + 0.01) difference() {
    inset2d(wall - 0.01);
    translate([dx, dy]) offset(r = c_clr) whoop2d(sq, duct_d);
    translate([wall - 1, cy_r]) offset(r = 1) offset(delta = -1) square([cx_in - wall + 1, yf - cy_r + 1]);
  }
}

// Window for the charging cable. The top corners are chamfered at 45 degrees, so
// the top is an 8 mm bridge.
module port_cut() {
  translate([0, Sy + 1, 0]) rotate([90, 0, 0]) linear_extrude(wall + 2)
    translate([px, pz]) polygon([[-7, -4.5], [7, -4.5], [7, 1.5], [4, 4.5], [-4, 4.5], [-7, 1.5]]);
}

// Dovetail channel in the outer face of the front wall, from under the window up
// through the rim. The slider sits flush in it and goes in from the top.
module slider_channel() {
  a = sl_w / 2 + 0.2;
  b = sl_w / 2 + sl_t + 0.2;
  translate([px, 0, sl_z0]) linear_extrude(zc + lip_h + 1 - sl_z0)
    polygon([[-a, Sy + 0.01], [a, Sy + 0.01], [b, Sy - sl_t], [b, Sy - sl_t - 0.3], [-b, Sy - sl_t - 0.3], [-b, Sy - sl_t]]);
}

// V grooves in the channel floor where the slider bump clicks in: closed and open.
module detents() {
  for (zg = [sl_z0 + 5, sl_z0 + 5 + sl_travel])
    translate([px + 8.5, 0, 0]) rotate([90, 0, 90]) linear_extrude(5)
      polygon([[Sy - sl_t - 0.29, zg - det], [Sy - sl_t - 0.3 - det, zg], [Sy - sl_t - 0.29, zg + det]]);
}

// Boss inside the front wall behind the latch pocket, with a 45 degree underside.
module latch_boss() {
  hull() {
    translate([Sx / 2 - 14, yf - 3, zc - latch_drop - 3]) cube([28, 3.01, latch_drop + 3]);
    translate([Sx / 2 - 14, yf - 0.01, zc - latch_drop - 6]) cube([28, 0.02, 0.01]);
  }
}

// Recess for the flush tongue, a 45 degree lead-in over the wall top, the pocket the
// hook catches in, a scoop for a fingernail under the tongue, and a notch in the
// rim lip where the tongue passes.
module latch_cut() {
  zt = zc - latch_drop;
  translate([Sx / 2 - latch_w / 2 - 0.5, 0, 0]) rotate([90, 0, 90]) linear_extrude(latch_w + 1) {
    translate([Sy - 1.9, zt - 0.5]) square([3, latch_drop + 2]);
    polygon([[Sy - 1.89, zc - 1], [Sy - 1.89, zc + 1], [Sy - 2.9, zc + 1], [Sy - 2.9, zc]]);
    polygon([[Sy - 1.89, zt - 0.2], [Sy - 2.9, zt + 0.81], [Sy - 2.9, zt + 1.59], [Sy - 1.89, zt + 2.6]]);
    polygon([[Sy - 1.9, zt - 0.49], [Sy + 1, zt - 0.49], [Sy + 1, zt - 3.4]]);
  }
  translate([Sx / 2 - latch_w / 2 - 0.6, Sy - wall - 0.2, zc - 0.01]) cube([latch_w + 1.2, wall + 1.2, lip_h + 1]);
}

module base() {
  difference() {
    union() {
      base_shell();
      knuckles(false);
      deck();
      latch_boss();
    }
    at_charger_springs() spring_socket();
    at_whoop_springs() spring_socket();
    port_cut();
    slider_channel();
    detents();
    latch_cut();
  }
}

// ---- Slider ----
// Prints front face down; its edges flare at 45 degrees into the dovetail. A tongue
// cut into it beside the window bends along its layers and carries a bump on the
// back that clicks into the grooves. Local frame: x across, y up the wall, z from
// the front face to the back face.

module slider_flat() {
  tx0 = sl_w / 2 + 9;
  difference() {
    hull() {
      cube([sl_w, sl_h, 0.01]);
      translate([-sl_t, 0, sl_t - 0.01]) cube([sl_w + 2 * sl_t, sl_h, 0.01]);
    }
    translate([tx0 - 0.7, 3.3, -1]) cube([5.4, 9.7, sl_t + 2]);
  }
  translate([tx0, 4, 0]) cube([4, 9.01, sl_t]);
  translate([tx0, 0, sl_t - 0.01]) rotate([90, 0, 90]) linear_extrude(4) polygon([[4, 0], [5, det], [6, 0]]);
}

module slider_placed() {
  multmatrix([[1, 0, 0, px - sl_w / 2], [0, 0, -1, Sy], [0, 1, 0, sl_z0], [0, 0, 0, 1]]) slider_flat();
}

// ---- Lid ----

module lid_shell() {
  difference() {
    translate([0, 0, zc]) hull() {
      linear_extrude(0.01) inset2d(seam_ch);
      translate([0, 0, seam_ch]) linear_extrude(lid_h - seam_ch - top_ch) outer2d();
      translate([0, 0, lid_h - 0.01]) linear_extrude(0.01) inset2d(top_ch);
    }
    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);
  }
}

// The tongue is the outer skin of the lid front, carried on down past the rim into
// the recess of the base. Its hook rides over the lead-in and catches in the pocket.
module latch_tongue() {
  zt = zc - latch_drop;
  translate([Sx / 2 - latch_w / 2, 0, 0]) rotate([90, 0, 90]) linear_extrude(latch_w) {
    translate([Sy - tongue_t, zt]) square([tongue_t, latch_drop + 4]);
    polygon([[Sy - tongue_t + 0.01, zt], [Sy - 2.7, zt + 1.1], [Sy - 2.7, zt + 1.3], [Sy - tongue_t + 0.01, zt + 2.4]]);
  }
}

// Two slits and a relief behind the tongue free its upper 4 mm from the lid wall,
// so it flexes over latch_drop plus 4 mm.
module tongue_relief() {
  for (s = [-1, 1]) translate([Sx / 2 + s * (latch_w / 2 + 0.3) - 0.3, Sy - wall - 1, zc - 1]) cube([0.6, wall + 2, 5]);
  translate([Sx / 2 - latch_w / 2 - 0.01, Sy - wall - 1, zc - 1]) cube([latch_w + 0.02, wall + 1 - tongue_t, 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() {
  difference() {
    union() {
      lid_shell();
      knuckles(true);
      bat_clips();
      latch_tongue();
    }
    tongue_relief();
  }
}

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

// ---- Spring sets, laid out flat for printing ----

module charger_springs_flat() {
  for (k = [0, 1]) translate([sp_slot, 8 + k * 18, 0]) serp_spring(c_len, 14, 12);
}

module whoop_springs_flat() {
  if (w_ok) for (k = [0 : 3]) translate([sp_slot, 7 + k * 16, 0]) serp_spring(w_len, 12, 10);
  else echo("whoop springs: the smaller whoop is too close in size to the pocket, no room for springs");
}

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

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

module ghost_charger() {
  color("OrangeRed", 0.5) translate([wall, yf - charger_l, 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 = 46;
  // 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 - 7, zc - latch_drop - 8], [Sx / 2 + 16, Sy + 0.1, zc + lip_h + 1]) base();
  translate([g, 22, 0]) coupon([Sx / 2 - 16, -0.1, 0], [Sx / 2 + 16, 7, lid_h + latch_drop + 1]) lid_print();
  // slider channel with the window, and the slider
  translate([2 * g, 0, 0]) coupon([px - 20, Sy - 5, sl_z0 - 3], [px + 20, Sy + 0.1, zc + 0.5]) base();
  translate([2 * g + 6, 12, 0]) slider_flat();
  // the inner charger spring socket with a piece of deck, and one charger spring
  translate([3 * g, 0, 0])
    coupon([cx_in - 8, yf - charger_l / 2 - 9, 0], [cx_in + sp_slot + 3, yf - charger_l / 2 + 9, fz + deck_h]) base();
  translate([3 * g + sp_slot, 30, 0]) serp_spring(c_len, 14, 12);
  // one battery clip
  if (battery_count > 0) {
    yc = Sy / 2 - 0.28 * battery_l;
    bx = bat_x(0);
    translate([4 * g, 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();
  color(color_case) slider_placed();
  color(color_case) at_charger_springs() serp_spring(c_len - sp_pre, 14, 12);
  if (show_insert && w_ok) color(color_case) at_whoop_springs() serp_spring(w_len - sp_pre, 12, 10);
  if (show_contents) {
    if (show_insert && w_ok) ghost_whoop(insert_wheelbase, insert_duct_d);
    else ghost_whoop(whoop_wheelbase, duct_d);
    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 if (part == "slider") color(color_case) slider_flat();
else if (part == "charger_springs") color(color_case) charger_springs_flat();
else if (part == "whoop_springs") color(color_case) whoop_springs_flat();
else assembly();