Wheeled bipedal balancer

// Wheeled bipedal balancer, printable parts.
// Two straight legs, each with a roll joint on the body, a pitch joint below
// it and a driven wheel. Two-shell chassis with electronics bays. Separate
// rigid hub and TPU tyre per wheel.

/* [Part] */
// What to render: the assembly, or one printable part in print orientation.
part = "assembly"; // [assembly, body_tray, body_lid, hip_bracket, leg, wheel_hub, tire]

/* [Actuators] */
// Hip actuator, used for both the roll and the pitch joint.
hip_actuator = "STS3250"; // [STS3215, STS3250]
// Wheel drive actuator, one per wheel.
wheel_actuator = "STS3215"; // [STS3215, STS3250]

/* [Leg] */
// Pitch pivot to wheel axle.
leg_length = 140; // [60:1:260]
// Diameter measured over the tyre tread.
wheel_diameter = 140; // [60:5:240]
// Width across the tyre.
wheel_width = 26; // [14:1:60]

/* [Body] */
// Fore-aft length of the chassis.
body_length = 150; // [120:1:200]
// Width of the chassis.
body_width = 80; // [70:1:140]
// Height of the chassis, tray plus lid.
body_height = 70; // [56:1:120]
// All-up mass for the torque check. Changes no geometry.
mass_g = 1200; // [400:50:3000]

/* [Pose] */
// Leg swung forward from vertical, degrees. Negative is back.
leg_pitch = 0; // [-60:1:60]
// Leg swung outward from vertical, degrees. Negative is in.
leg_roll = 0; // [-30:1:45]

/* [Sensor] */
// What sits on the body.
sensor = "lidar"; // [none, lidar, camera, both]

/* [Hidden] */
$fn = 36;
wall = 2.4;
corner_r = 8;
corner_in = 9;           // screw post inset from the corner
split_z = 46;            // tray height; lid takes the rest
hip_z = 34;              // roll axis above the tray floor
insert_d = 4.0;          // M3 heat-set insert hole
m3_clear = 3.4;
m3_head = 6.4;
m2_hole = 2.2;
horn_circle = 14;        // horn bolt circle, 4 holes -- measure your horn
horn_hole = 2.2;
horn_thick = 6;          // servo face to mating face, horn included
shaft_off = 10;          // shaft centre from the near end of the case -- check
side_hole_in = 6;        // side mounting holes inset from case ends/faces -- measure
face_hx = 10;            // top-face mounting holes around the shaft -- measure
face_hz = 8;
lt = 6;                  // leg plate thickness
pt = 3;                  // bracket plate thickness
tire_t = 12;             // tyre radial thickness
tread_n = 28;

// Servo case [L, W, H]. Shaft on the L x W face, shaft_off from one L end.
function act_size(n)  = n == "STS3250" ? [45.2, 24.7, 35.0] : [44.8, 24.0, 35.5];
function act_stall(n) = n == "STS3250" ? 50 : 30;

hip_size  = act_size(hip_actuator);
whl_size  = act_size(wheel_actuator);
hip_stall = act_stall(hip_actuator);
whl_stall = act_stall(wheel_actuator);
hip_rated = hip_stall * 0.25;

rL = hip_size[0]; rW = hip_size[1]; rH = hip_size[2];
wheel_r = wheel_diameter / 2;
mass_kg = mass_g / 1000;
lid_h   = body_height - split_z;

// Right-leg frame, origin on the roll axis. Left leg is a mirror.
roll_y       = body_width / 2 + rW / 2;
shelf_top    = -(rL - shaft_off) - 1;
pitch_face_y = -rW / 2 + rH;
pitch_z      = shelf_top - pt - 0.5 - rW / 2;
leg_y_in     = pitch_face_y + horn_thick;
wheel_yl     = leg_y_in + lt + horn_thick + wheel_width / 2;

// Wheel centre in world coordinates, right leg.
zz   = pitch_z - leg_length * cos(leg_pitch);
wy_r = wheel_yl * cos(leg_roll) - zz * sin(leg_roll);
wz_r = wheel_yl * sin(leg_roll) + zz * cos(leg_roll);
wc_y = roll_y + wy_r;
wc_z = hip_z + wz_r;

ground_z = wc_z - wheel_r * cos(leg_roll);
stance_h = -ground_z;
track_w  = 2 * wc_y + wheel_width * cos(leg_roll);
sensor_h = (sensor == "lidar" || sensor == "both") ? 36 : 0;
total_h  = stance_h + body_height + sensor_h;

pitch_need = abs(mass_kg / 2 * leg_length * sin(leg_pitch) / 10);
roll_need  = abs(mass_kg / 2 * wy_r / 10);
roll_stand = mass_kg / 2 * wheel_yl / 10;
arm_lim    = hip_rated / (mass_kg / 2);
pitch_max  = arm_lim >= leg_length / 10 ? 90 : asin(arm_lim / (leg_length / 10));
rim_force  = whl_stall / (wheel_r / 10);
leg_print  = leg_length + 34;

// Electronics bay positions along x, front is +x.
pi_x  = body_length / 2 - wall - 4 - 32.5;
bat_x = -body_length / 2 + wall + 4 + 20.5;
drv_x = ((pi_x - 32.5) + (bat_x + 20.5)) / 2;
lidar_x = body_length / 4;

echo(str("stance height, tray floor to ground: ", round(stance_h), " mm; overall ", round(total_h), " mm; track ", round(track_w), " mm"));
echo(str("pitch joint: ", round(pitch_need*10)/10, " kg.cm now, holds up to ", round(pitch_max), " deg on ", hip_rated, " kg.cm rated"));
echo(str("roll joint: ", round(roll_need*10)/10, " kg.cm now; ", round(roll_stand*10)/10, " kg.cm just standing, from the wheel offset"));
echo(str("wheel rim force at stall: ", round(rim_force*10)/10, " kg against ", mass_kg, " kg"));
echo(str("bed check (180 mm): body ", body_length, ", wheel ", wheel_diameter, ", leg ", leg_print, leg_print > 180 ? " -- lay the leg diagonally" : ""));
echo("fasteners: 4x M3 heat-set insert, 4x M3x10 (lid); servo M2 screws for hips, brackets, legs and hubs; tyre snaps on");

// ---------- primitives ----------
module rbox(l, w, h, r) {
  hull() for (sx = [-1, 1], sy = [-1, 1])
    translate([sx * (l / 2 - r), sy * (w / 2 - r), 0]) cylinder(h = h, r = r);
}

// Servo with shaft along +z, shaft centre at the origin, case below z=0.
module servo(sz) {
  color("Goldenrod") {
    translate([-shaft_off, -sz[1] / 2, -sz[2]]) cube([sz[0], sz[1], sz[2]]);
    cylinder(h = 4, d = 6);
  }
}

module horn_holes(h) {
  for (a = [0 : 90 : 270]) rotate([0, 0, a])
    translate([horn_circle / 2, 0, 0]) cylinder(h = h, d = horn_hole, center = true);
}

// ---------- body tray ----------
module battery_rib() {
  difference() {
    translate([-23, -1.5, 0]) cube([46, 3, wall + 14]);
    for (i = [-1, 1]) translate([i * 10.5, 0, wall + 11])
      rotate([90, 0, 0]) cylinder(h = 5, d = 19, center = true);
  }
}

module body_tray() {
  difference() {
    union() {
      difference() {
        rbox(body_length, body_width, split_z, corner_r);
        translate([0, 0, wall]) rbox(body_length - 2 * wall, body_width - 2 * wall, split_z, corner_r - wall);
      }
      for (sx = [-1, 1], sy = [-1, 1])
        translate([sx * (body_length / 2 - corner_in), sy * (body_width / 2 - corner_in), 0]) cylinder(h = split_z, d = 9);
      for (sx = [-1, 1], sy = [-1, 1])
        translate([pi_x + sx * 29, sy * 11.5, 0]) cylinder(h = wall + 5, d = 5.5);
      for (sx = [-1, 1])
        translate([drv_x + sx * 20, 0, 0]) cylinder(h = wall + 5, d = 5.5);
      for (sy = [-1, 1]) translate([bat_x, sy * 30, 0]) battery_rib();
    }
    for (sx = [-1, 1], sy = [-1, 1])
      translate([sx * (body_length / 2 - corner_in), sy * (body_width / 2 - corner_in), split_z - 8]) cylinder(h = 9, d = insert_d);
    for (sx = [-1, 1], sy = [-1, 1])
      translate([pi_x + sx * 29, sy * 11.5, wall]) cylinder(h = 6, d = m2_hole);
    for (sx = [-1, 1])
      translate([drv_x + sx * 20, 0, wall]) cylinder(h = 6, d = m2_hole);
    // roll servo mounting screws through the side walls
    for (side = [-1, 1], hx = [-(rH - side_hole_in), -side_hole_in], hz = [shaft_off - side_hole_in, -(rL - shaft_off - side_hole_in)])
      translate([hx, side * body_width / 2, hip_z + hz]) rotate([90, 0, 0]) cylinder(h = wall * 3, d = m2_hole, center = true);
    // vents, front and rear thirds of each side
    for (side = [-1, 1], i = [0 : 3]) {
      translate([body_length / 2 - 16 - i * 9, side * body_width / 2, split_z / 2 + 4]) rotate([0, 20, 0]) cube([3, wall * 3, 18], center = true);
      translate([-body_length / 2 + 16 + i * 9, side * body_width / 2, split_z / 2 + 4]) rotate([0, -20, 0]) cube([3, wall * 3, 18], center = true);
    }
    // rear switch or charge lead
    translate([-body_length / 2, 0, split_z - 12]) cube([wall * 3, 14, 9], center = true);
  }
}

// ---------- body lid ----------
module body_lid() {
  difference() {
    union() {
      hull() {
        rbox(body_length, body_width, 1, corner_r);
        translate([0, 0, lid_h - 1]) rbox(body_length - 10, body_width - 10, 1, corner_r - 4);
      }
      translate([0, 0, -4]) rbox(body_length - 2 * wall - 0.6, body_width - 2 * wall - 0.6, 4.01, corner_r - wall);
      for (sx = [-1, 1], sy = [-1, 1])
        translate([sx * (body_length / 2 - corner_in), sy * (body_width / 2 - corner_in), -4]) cylinder(h = lid_h + 4, d = 9);
      if (sensor == "lidar" || sensor == "both")
        translate([lidar_x, 0, lid_h - 0.01]) cylinder(h = 3, d = 44);
      for (sx = [-1, 1]) translate([sx * 9, 0, wall]) cylinder(h = lid_h - 2 * wall - 4, d = 5);
    }
    translate([0, 0, -5]) rbox(body_length - 4 * wall - 0.6, body_width - 4 * wall - 0.6, lid_h - wall + 5, corner_r - 2 * wall);
    for (sx = [-1, 1], sy = [-1, 1]) {
      translate([sx * (body_length / 2 - corner_in), sy * (body_width / 2 - corner_in), -5]) cylinder(h = lid_h + 10, d = m3_clear);
      translate([sx * (body_length / 2 - corner_in), sy * (body_width / 2 - corner_in), lid_h - 3.5]) cylinder(h = 6, d = m3_head);
    }
    if (sensor == "lidar" || sensor == "both")
      translate([lidar_x, 0, lid_h - 10]) {
        cylinder(h = 20, d = 12);
        for (a = [45 : 90 : 315]) rotate([0, 0, a]) translate([15, 0, 0]) cylinder(h = 20, d = 2.7);
      }
    if (sensor == "camera" || sensor == "both")
      translate([body_length / 2 - 5, 0, lid_h / 2]) cube([16, 26, 12], center = true);
    for (sx = [-1, 1]) translate([sx * 9, 0, wall]) cylinder(h = 5, d = m2_hole);
  }
}

// ---------- hip bracket (right leg frame) ----------
module hip_bracket() {
  difference() {
    union() {
      translate([horn_thick - pt, -rW / 2 - 1, shelf_top - pt])
        cube([pt, rW + 2, shaft_off + 4 - (shelf_top - pt)]);
      translate([-14, -rW / 2 + 0.5, shelf_top - pt])
        cube([rL - shaft_off + 16, rH + 0.5, pt]);
      // gusset between plate and shelf on the outboard edge
      hull() {
        translate([horn_thick - pt, rW / 2 - 2, shelf_top]) cube([pt, 3, 12]);
        translate([horn_thick - pt, rW / 2 - 2, shelf_top - pt]) cube([12, 3, pt]);
      }
    }
    rotate([0, 90, 0]) { horn_holes(20); cylinder(h = 20, d = 8, center = true); }
    for (hx = [-shaft_off + side_hole_in, rL - shaft_off - side_hole_in], hy = [pitch_face_y - rH + side_hole_in, pitch_face_y - side_hole_in])
      translate([hx, hy, shelf_top - pt - 1]) cylinder(h = pt + 2, d = m2_hole);
  }
}

// ---------- leg (pitch axis at origin, plate normal y, leg down -z) ----------
module leg() {
  n = max(1, floor((leg_length - 70) / 30));
  slot = (leg_length - 70) / n - 6;
  difference() {
    hull() {
      rotate([90, 0, 0]) cylinder(h = lt, d = 34, center = true);
      translate([0, 0, -leg_length]) rotate([90, 0, 0]) cylinder(h = lt, d = 30, center = true);
    }
    rotate([90, 0, 0]) { horn_holes(20); cylinder(h = 20, d = 8, center = true); }
    for (i = [0 : n - 1])
      translate([0, 0, -35 - slot / 2 - i * (slot + 6)])
        rotate([90, 0, 0]) hull() {
          translate([0,  slot / 2 - 5, 0]) cylinder(h = lt * 3, d = 10, center = true);
          translate([0, -slot / 2 + 5, 0]) cylinder(h = lt * 3, d = 10, center = true);
        }
    translate([0, 0, -leg_length]) rotate([90, 0, 0]) {
      cylinder(h = 20, d = 8, center = true);
      for (sx = [-1, 1], sz = [-1, 1]) translate([sx * face_hx, sz * face_hz, 0]) cylinder(h = 20, d = m2_hole, center = true);
    }
  }
}

// ---------- wheel hub and tyre (axis z, hub face at z=0) ----------
rim_d = wheel_diameter - 2 * tire_t;

module wheel_hub() {
  web_t = 6;
  difference() {
    union() {
      difference() {
        cylinder(h = wheel_width, d = rim_d);
        translate([0, 0, -1]) cylinder(h = wheel_width + 2, d = rim_d - 6);
      }
      cylinder(h = web_t, d = rim_d - 5);
    }
    for (a = [0 : 72 : 359]) rotate([0, 0, a + 36]) translate([0, 0, -1]) hull() {
      translate([0, 22, 0]) cylinder(h = web_t + 2, d = 10);
      translate([0, rim_d / 2 - 14, 0]) cylinder(h = web_t + 2, d = 20);
    }
    translate([0, 0, wheel_width / 2]) rotate_extrude() translate([rim_d / 2, 0]) circle(d = 3);
    translate([0, 0, -1]) cylinder(h = web_t + 2, d = 8);
    translate([0, 0, web_t / 2]) horn_holes(web_t + 2);
  }
}

module tire() {
  color("DimGray") difference() {
    rotate_extrude() hull() {
      translate([rim_d / 2 + 0.2, 0]) square([0.01, wheel_width]);
      translate([wheel_diameter / 2 - 4, 4]) circle(r = 4);
      translate([wheel_diameter / 2 - 4, wheel_width - 4]) circle(r = 4);
    }
    for (i = [0 : tread_n - 1]) rotate([0, 0, i * 360 / tread_n])
      translate([wheel_diameter / 2, 0, wheel_width / 2]) rotate([15, 0, 0]) cube([4, 2.2, wheel_width * 2], center = true);
  }
  color("DimGray") translate([0, 0, wheel_width / 2]) rotate_extrude() translate([rim_d / 2 + 0.2, 0]) circle(d = 2.6);
}

// ---------- assembly ----------
module right_leg_assembly() {
  rotate([0, 90, 0]) servo(hip_size);
  rotate([leg_roll, 0, 0]) {
    color("Silver") hip_bracket();
    translate([0, pitch_face_y, pitch_z]) rotate([-90, 0, 0]) servo(hip_size);
    translate([0, 0, pitch_z]) rotate([0, -leg_pitch, 0]) {
      color("Silver") translate([0, leg_y_in + lt / 2, 0]) leg();
      translate([0, leg_y_in, -leg_length]) rotate([-90, 0, 0]) servo(whl_size);
      translate([0, leg_y_in + lt + horn_thick, -leg_length]) rotate([-90, 0, 0]) {
        color("Gainsboro") wheel_hub();
        tire();
      }
    }
  }
}

module assembly() {
  color("SteelBlue") body_tray();
  color("SteelBlue") translate([0, 0, split_z]) body_lid();
  if (sensor == "lidar" || sensor == "both")
    color("DimGray") translate([lidar_x, 0, body_height + 3]) cylinder(h = 33, d = 38);
  translate([0, roll_y, hip_z]) right_leg_assembly();
  mirror([0, 1, 0]) translate([0, roll_y, hip_z]) right_leg_assembly();
  color("Gainsboro") translate([0, 0, ground_z - 3]) cube([500, track_w + 160, 6], center = true);
}

if (part == "assembly") assembly();
else if (part == "body_tray") body_tray();
else if (part == "body_lid") translate([0, 0, lid_h]) mirror([0, 0, 1]) body_lid();
else if (part == "hip_bracket") translate([0, 0, horn_thick]) rotate([0, 90, 0]) hip_bracket();
else if (part == "leg") translate([0, 0, lt / 2]) rotate([90, 0, 0]) leg();
else if (part == "wheel_hub") wheel_hub();
else if (part == "tire") tire();