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assets/local_juice_shot: 59 mL sim2real juice-shot bottle, fine-pitch screw cap

#23

by jxxsteven7 - opened 7 days ago

base: refs/heads/main

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from: refs/pr/23

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assets/local_juice_shot/gen_juice_shot_meshes.py +247 -0
assets/local_juice_shot/juice_shot.urdf +95 -0
assets/local_juice_shot/juice_shot.xml +123 -0
assets/local_juice_shot/meshes/shot_body.obj +0 -0
assets/local_juice_shot/meshes/shot_cap.obj +0 -0
assets/local_juice_shot/meshes/shot_neck.obj +0 -0
assets/local_juice_shot/meshes/shot_thread.obj +0 -0

assets/local_juice_shot/gen_juice_shot_meshes.py ADDED Viewed

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+"""Generate the juice-shot bottle + fine-pitch screw-cap meshes (OBJ) for juice_shot.xml.
+Deterministic, numpy-only lathe/sweep generator (same conventions as
+local_bottle_cap/gen_bottle_cap_meshes.py — re-running reproduces the shipped
+``meshes/*.obj`` byte-for-byte). Run with any python that has numpy:
+    python gen_juice_shot_meshes.py            # writes ./meshes/*.obj
+REAL-WORLD REFERENCE (sim2real target): Trader Joe's Organic Mighty Turmeric
+juice shot, NET 2 fl oz / 59 mL, measured/derived from the maintainer's
+reference photos (bottle vs. an adult hand) + standard PET shot-bottle specs:
+    total height (closed) ........ ~85 mm
+    body outer diameter .......... ~38 mm  (2 oz PET shot standard)
+    cap outer diameter ........... ~29 mm, height ~15.5 mm, white, fine ribs
+    neck support flange OD ....... ~33 mm  (the wide ring under the cap)
+    tamper-evident band .......... stays on the NECK below the cap skirt
+    thread ....................... single-start FINE pitch 3.0 mm/turn
+                                   (reference: 28 mm PCO-1881 beverage finish
+                                   = 2.7 mm/turn); cap disengages after
+                                   ~1.7 turns ≈ 5 mm of rise
+    contents ..................... coconut water + turmeric + lemon → pale
+                                   translucent yellow liquid
+    filled mass .................. ~75 g (59 g juice + ~11 g PET + ~5 g cap)
+Meshes (bottle frame: origin at the base centre, +z up, metres):
+  - shot_body.obj    translucent PET: base chamfer, straight wall, shoulder,
+                     smooth lower neck
+  - shot_neck.obj    frosted threaded neck section + opening lip + the wide
+                     support flange + the tamper-evident band ring
+  - shot_thread.obj  helical thread ridge — pitch is THREAD_PITCH_M_PER_TURN,
+                     the SAME constant the MJCF screw equality (polycoef) and
+                     the task's SCREW_PITCH_M_PER_RAD derive from
+  - shot_cap.obj     white ribbed cap (cap frame: origin at the closed mount,
+                     the MJCF ``<body name="cap" pos="0 0 0.069">``)
+"""
+from __future__ import annotations
+import os
+import numpy as np
+# ── The one mechanism constant (mirrored by juice_shot.xml + the task file) ──
+THREAD_PITCH_M_PER_TURN = 0.003  # cap rises 3 mm per full turn (fine, real-world)
+# ── Bottle dimensions (metres, bottle-local z), photo-referenced ─────────────
+BODY_R = 0.019      # 38 mm OD
+BODY_TOP_Z = 0.052  # shoulder starts
+NECK_R = 0.0125     # smooth visible neck
+FLANGE_R = 0.0165   # 33 mm support flange
+FLANGE_Z = 0.0665
+THREAD_NECK_R = 0.0122
+THREAD_NECK_Z0 = 0.0685
+NECK_TOP_Z = 0.082  # opening lip
+CAP_MOUNT_Z = 0.069  # cap body origin (== checker closed_rel_pos_m z)
+CAP_R = 0.0145      # 29 mm OD
+CAP_H = 0.0155
+THREAD_Z0 = 0.0715  # first thread-turn centreline
+THREAD_TURNS = 2.4
+THREAD_TUBE_R = 0.0009
+THREAD_RIDE_R = THREAD_NECK_R + 0.0004
+SEG = 96
+RIB_LOBES = 44      # fine vertical ribs on the white cap
+RIB_AMP = 0.00045
+def _accumulate_normals(verts: np.ndarray, faces: np.ndarray) -> np.ndarray:
+    normals = np.zeros_like(verts)
+    tri = verts[faces]
+    fn = np.cross(tri[:, 1] - tri[:, 0], tri[:, 2] - tri[:, 0])
+    for k in range(3):
+        np.add.at(normals, faces[:, k], fn)
+    lens = np.linalg.norm(normals, axis=1, keepdims=True)
+    lens[lens < 1e-12] = 1.0
+    return normals / lens
+def _write_obj(path: str, verts: np.ndarray, faces: np.ndarray) -> None:
+    normals = _accumulate_normals(verts, faces)
+    lines = [f"v {v[0]:.6f} {v[1]:.6f} {v[2]:.6f}" for v in verts]
+    lines += [f"vn {n[0]:.6f} {n[1]:.6f} {n[2]:.6f}" for n in normals]
+    lines += [f"f {a}//{a} {b}//{b} {c}//{c}" for a, b, c in (faces + 1)]
+    with open(path, "w") as f:
+        f.write("\n".join(lines) + "\n")
+    print(f"wrote {path}: {len(verts)} verts, {len(faces)} tris")
+def lathe(profile, *, seg: int = SEG, close_bottom=False, close_top=False, rib_rows=None):
+    theta = np.linspace(0.0, 2.0 * np.pi, seg, endpoint=False)
+    rows = []
+    for i, (r, z) in enumerate(profile):
+        rr = np.full(seg, r)
+        if rib_rows is not None and rib_rows[0] <= i <= rib_rows[1]:
+            rr = rr + RIB_AMP * np.cos(RIB_LOBES * theta)
+        rows.append(np.stack([rr * np.cos(theta), rr * np.sin(theta), np.full(seg, z)], axis=1))
+    verts = np.concatenate(rows, axis=0)
+    faces = []
+    for i in range(len(profile) - 1):
+        a0, b0 = i * seg, (i + 1) * seg
+        for j in range(seg):
+            jn = (j + 1) % seg
+            faces.append([a0 + j, a0 + jn, b0 + jn])
+            faces.append([a0 + j, b0 + jn, b0 + j])
+    if close_bottom:
+        c = len(verts)
+        verts = np.vstack([verts, [0.0, 0.0, profile[0][1]]])
+        for j in range(seg):
+            faces.append([c, (j + 1) % seg, j])
+    if close_top:
+        c = len(verts)
+        base = (len(profile) - 1) * seg
+        verts = np.vstack([verts, [0.0, 0.0, profile[-1][1]]])
+        for j in range(seg):
+            faces.append([c, base + j, base + (j + 1) % seg])
+    return verts, np.asarray(faces, dtype=np.int64)
+def _arc(p0, p1, n):
+    (r0, z0), (r1, z1) = p0, p1
+    ts = np.linspace(0.0, 1.0, n + 2)[1:-1]
+    out = []
+    for t in ts:
+        s = t * t * (3.0 - 2.0 * t)
+        out.append((float(r0 + (r1 - r0) * s), float(z0 + (z1 - z0) * t)))
+    return out
+def shot_body():
+    profile = [
+        (0.0165, 0.0000),
+        (0.0188, 0.0025),
+        (BODY_R, 0.0060),
+        (BODY_R, BODY_TOP_Z - 0.004),
+        *_arc((BODY_R, BODY_TOP_Z - 0.004), (NECK_R, 0.0615), 6),
+        (NECK_R, 0.0615),
+        (NECK_R, FLANGE_Z),  # smooth neck up to the flange
+    ]
+    return lathe(profile, close_bottom=True)
+def shot_neck():
+    """Flange + tamper band + threaded neck + opening lip, one frosted mesh."""
+    profile = [
+        (NECK_R, 0.0655),          # overlap the body-neck seam
+        (FLANGE_R, 0.0658),        # support flange underside
+        (FLANGE_R, FLANGE_Z + 0.0014),
+        (0.0148, FLANGE_Z + 0.0016),   # step in above the flange…
+        (0.0148, THREAD_NECK_Z0 + 0.0012),  # …the tamper-evident band ring
+        (THREAD_NECK_R, THREAD_NECK_Z0 + 0.0016),
+        (THREAD_NECK_R, NECK_TOP_Z - 0.001),
+        (0.0128, NECK_TOP_Z),      # opening lip, slightly out
+        (0.0102, NECK_TOP_Z),      # rim
+        (0.0098, NECK_TOP_Z - 0.005),  # short inner descent → dark mouth
+    ]
+    return lathe(profile, close_top=True)
+def shot_thread():
+    n_along, n_around = 300, 10
+    phi = np.linspace(0.0, 2.0 * np.pi * THREAD_TURNS, n_along)
+    z = THREAD_Z0 + THREAD_PITCH_M_PER_TURN * phi / (2.0 * np.pi)
+    t = np.linspace(0.0, 1.0, n_along)
+    taper = np.clip(np.minimum(t, 1.0 - t) / 0.08, 0.0, 1.0)
+    tube_r = THREAD_TUBE_R * (0.15 + 0.85 * taper)
+    path = np.stack([THREAD_RIDE_R * np.cos(phi), THREAD_RIDE_R * np.sin(phi), z], axis=1)
+    tangent = np.gradient(path, axis=0)
+    tangent /= np.linalg.norm(tangent, axis=1, keepdims=True)
+    outward = np.stack([np.cos(phi), np.sin(phi), np.zeros_like(phi)], axis=1)
+    side = np.cross(tangent, outward)
+    side /= np.linalg.norm(side, axis=1, keepdims=True)
+    psi = np.linspace(0.0, 2.0 * np.pi, n_around, endpoint=False)
+    verts = (
+        path[:, None, :]
+        + tube_r[:, None, None] * (np.cos(psi)[None, :, None] * outward[:, None, :])
+        + tube_r[:, None, None] * (np.sin(psi)[None, :, None] * side[:, None, :])
+    ).reshape(-1, 3)
+    faces = []
+    for i in range(n_along - 1):
+        a0, b0 = i * n_around, (i + 1) * n_around
+        for j in range(n_around):
+            jn = (j + 1) % n_around
+            faces.append([a0 + j, b0 + j, b0 + jn])
+            faces.append([a0 + j, b0 + jn, a0 + jn])
+    for base in (0, (n_along - 1) * n_around):
+        c = len(verts)
+        i = 0 if base == 0 else n_along - 1
+        verts = np.vstack([verts, path[i]])
+        for j in range(n_around):
+            jn = (j + 1) % n_around
+            faces.append([c, base + jn, base + j] if base == 0 else [c, base + j, base + jn])
+    faces = np.asarray(faces, dtype=np.int64)
+    # Same left-handed frame as the bottle_cap generator — flip once for
+    # outward normals (verified there: -0.998 before, +0.998 after).
+    return verts, faces[:, [0, 2, 1]]
+def shot_cap():
+    """White ribbed cap in the cap body frame (origin = closed mount plane)."""
+    wall = [
+        (0.0138, 0.0000),
+        (CAP_R, 0.0018),
+        (CAP_R, 0.0040),
+        (CAP_R, 0.0065),
+        (CAP_R, 0.0090),
+        (CAP_R, 0.0115),
+        (CAP_R, 0.0128),
+        *_arc((CAP_R, 0.0128), (0.0110, CAP_H - 0.0004), 4),
+        (0.0110, CAP_H - 0.0004),
+        (0.0045, CAP_H),
+    ]
+    inner = [
+        (0.0045, CAP_H),
+        (0.0126, 0.0122),
+        (0.0126, 0.0006),
+        (0.0138, 0.0000),
+    ]
+    profile = wall + inner
+    v, f = lathe(profile, rib_rows=(1, 6))
+    c = len(v)
+    v = np.vstack([v, [0.0, 0.0, CAP_H]])
+    seg = SEG
+    top_row = (len(wall) - 1) * seg
+    faces = f.tolist()
+    for j in range(seg):
+        faces.append([c, top_row + j, top_row + (j + 1) % seg])
+    return v, np.asarray(faces, dtype=np.int64)
+def main() -> None:
+    out = os.path.join(os.path.dirname(os.path.abspath(__file__)), "meshes")
+    os.makedirs(out, exist_ok=True)
+    for name, build in (
+        ("shot_body", shot_body),
+        ("shot_neck", shot_neck),
+        ("shot_thread", shot_thread),
+        ("shot_cap", shot_cap),
+    ):
+        verts, faces = build()
+        _write_obj(os.path.join(out, f"{name}.obj"), verts, faces)
+if __name__ == "__main__":
+    main()

assets/local_juice_shot/juice_shot.urdf ADDED Viewed

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+<?xml version="1.0"?>
+<!-- URDF twin of juice_shot.xml (fine-pitch screw cap), for the IsaacSim USD
+     conversion only (MuJoCo loads the MJCF directly). Generate the USD in the
+     Isaac env with:
+       python scripts/convert_board_nail_urdf_to_usd.py \
+         - -urdf roboverse_data/assets/local_juice_shot/juice_shot.urdf \
+         - -root-link bottle - -out roboverse_data/assets/local_juice_shot/usd/juice_shot.usd
+     (drop the space in the flags; '-' '-' inside an XML comment is illegal).
+     The root is FLOATING on the Isaac side — the cfg loads it with
+     fix_base_link=False, matching the MuJoCo freejoint.
+     SCREW COUPLING CAVEAT (same as bottle_cap.urdf): URDF cannot express the
+     MJCF joint equality (cap_slide = 0.000477465 * cap_twist, 3 mm/turn), so
+     this twin chains the two joints WITHOUT the coupling; wiring it on the
+     Isaac side is part of the documented one-time USD conversion follow-up.
+     MuJoCo — the physics backend of record — is unaffected.
+     Real-world reference (sim2real): Trader Joe's Organic Mighty Turmeric
+     juice shot, 2 fl oz / 59 mL — ~85 mm tall, 38 mm body, 29 mm white ribbed
+     cap, 33 mm support flange, thread 3.0 mm/turn (28 mm PCO-1881 reference
+     2.7 mm), ~1.7 turns to open, ~75 g filled. -->
+<robot name="juice_shot">
+  <link name="bottle">
+    <inertial>
+      <origin xyz="0 0 0.032"/>
+      <mass value="0.068"/>
+      <inertia ixx="0.00004" iyy="0.00004" izz="0.000015" ixy="0" ixz="0" iyz="0"/>
+    </inertial>
+    <visual>
+      <geometry><mesh filename="meshes/shot_body.obj"/></geometry>
+    </visual>
+    <visual>
+      <geometry><mesh filename="meshes/shot_neck.obj"/></geometry>
+    </visual>
+    <visual>
+      <geometry><mesh filename="meshes/shot_thread.obj"/></geometry>
+    </visual>
+    <collision>
+      <origin xyz="0 0 0.026"/>
+      <geometry><cylinder radius="0.019" length="0.052"/></geometry>
+    </collision>
+    <collision>
+      <origin xyz="0 0 0.0595"/>
+      <geometry><cylinder radius="0.0125" length="0.015"/></geometry>
+    </collision>
+    <collision>
+      <origin xyz="0 0 0.0665"/>
+      <geometry><cylinder radius="0.0165" length="0.002"/></geometry>
+    </collision>
+    <collision>
+      <origin xyz="0 0 0.0745"/>
+      <geometry><cylinder radius="0.0122" length="0.015"/></geometry>
+    </collision>
+  </link>
+  <link name="cap_screw">
+    <!-- Massless carrier for the twist DOF (URDF needs one link per joint). -->
+    <inertial>
+      <origin xyz="0 0 0.008"/>
+      <mass value="0.001"/>
+      <inertia ixx="0.0000002" iyy="0.0000002" izz="0.0000002" ixy="0" ixz="0" iyz="0"/>
+    </inertial>
+  </link>
+  <link name="cap">
+    <inertial>
+      <origin xyz="0 0 0.008"/>
+      <mass value="0.0095"/>
+      <inertia ixx="0.0000008" iyy="0.0000008" izz="0.000001" ixy="0" ixz="0" iyz="0"/>
+    </inertial>
+    <visual>
+      <geometry><mesh filename="meshes/shot_cap.obj"/></geometry>
+    </visual>
+    <collision>
+      <origin xyz="0 0 0.00775"/>
+      <geometry><cylinder radius="0.0145" length="0.0155"/></geometry>
+    </collision>
+  </link>
+  <joint name="cap_twist" type="revolute">
+    <parent link="bottle"/>
+    <child link="cap_screw"/>
+    <origin xyz="0 0 0.069"/>
+    <axis xyz="0 0 1"/>
+    <limit lower="0.0" upper="16.7552" effort="2" velocity="20.0"/>
+    <dynamics damping="0.005" friction="0.02"/>
+  </joint>
+  <joint name="cap_slide" type="prismatic">
+    <parent link="cap_screw"/>
+    <child link="cap"/>
+    <origin xyz="0 0 0"/>
+    <axis xyz="0 0 1"/>
+    <limit lower="0.0" upper="0.008" effort="50" velocity="0.5"/>
+    <dynamics damping="0.2" friction="0.0"/>
+  </joint>
+</robot>

assets/local_juice_shot/juice_shot.xml ADDED Viewed

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+<mujoco model="juice_shot">
+  <!-- 59 mL juice-shot bottle + FINE-PITCH screw cap for the open_juice_shot
+       task — a sim2real twin of a real retail bottle (Trader Joe's Organic
+       Mighty Turmeric juice shot, NET 2 fl oz / 59 mL), dimensioned from the
+       maintainer's reference photos + standard PET shot-bottle specs:
+         total height (closed)  ~85 mm     body OD          ~38 mm
+         cap OD                 ~29 mm     cap height       ~15.5 mm
+         support flange OD      ~33 mm     tamper band      stays on the neck
+         thread pitch           3.0 mm/turn, single-start FINE
+                                (reference: 28 mm PCO-1881 beverage finish =
+                                2.7 mm/turn), ~1.7 turns to disengage
+         filled mass            ~75 g (59 g juice + ~11 g PET + ~5 g cap)
+       The cap is the same screw mechanism as local_bottle_cap v2 — SLIDE
+       (cap_slide, listed FIRST for the parrot_sim overlay's first-joint
+       contract) + coaxial HINGE (cap_twist), tied by the joint equality below:
+       slide = PITCH * twist, PITCH = 0.003 / 2π = 0.000477465 m/rad. The only
+       way the cap rises is by TURNING counter-clockwise: ~1.7 turns to the
+       task's 5 mm gate, ~2.7 turns to the 8 mm stop. Dry thread friction
+       (0.02 N·m) means a straight pull must back-drive the FINE screw at
+       ≈ frictionloss / PITCH ≈ 42 N — the finer pitch gives the thread MORE
+       mechanical advantage than the big bottle's 18 mm/turn, so this tiny cap
+       is even harder to yank off, exactly as with real beverage closures
+       (measured: 20 N pulls deflect ~0.45 mm elastically; ~42 N+ slips the
+       thread and the cap backs off ROTATING, like a stripped real cap).
+       The BOTTLE BASE IS FREE (cfg fix_base_link=False): at ~75 g the bottle
+       spins with the cap unless the other hand pins it — bimanual by
+       mechanics, and light enough that a table-friction-only "no-hands" cheat
+       does not exist.
+       Modeling notes (shared with bottle_cap.xml v2 — see its header for the
+       full rationale):
+       - explicit cap<->bottle contact exclude: MuJoCo's parent-child filter
+         is SKIPPED when the parent welds to the world, i.e. exactly in the
+         fixed-base standalone loads the asset regression tests use;
+       - solreffriction stiffens the friction constraint (no creep: cap weight
+         back-drives at ~4e-5 N·m, 500x below the 0.02 N·m thread friction);
+       - collision = primitive cylinders (group 3, hidden) with the calibrated
+         grasp friction/priority; visuals = group-1 meshes from
+         gen_juice_shot_meshes.py (deterministic; the visible thread helix is
+         generated at the SAME 3 mm/turn pitch as the equality);
+       - the juice visual cylinder carries the liquid mass (density 1000);
+       - success is the cap's base-relative displacement (articulated_open,
+         min_open_m = 0.005): qpos 0 = closed, slide range top 0.008;
+         cap origin (0 0 0.069) == the checker's closed_rel_pos_m;
+       - loaded as ArticulationObjCfg(fix_base_link=False); the root body
+         carries no pos/quat (set via the cfg default_position). -->
+  <compiler angle="radian" meshdir="meshes"/>
+  <asset>
+    <mesh name="shot_body_mesh" file="shot_body.obj"/>
+    <mesh name="shot_neck_mesh" file="shot_neck.obj"/>
+    <mesh name="shot_thread_mesh" file="shot_thread.obj"/>
+    <mesh name="shot_cap_mesh" file="shot_cap.obj"/>
+    <material name="mat_pet" rgba="0.92 0.94 0.96 0.22" specular="0.9" shininess="0.9"/>
+    <material name="mat_juice" rgba="0.93 0.85 0.55 0.55" specular="0.5" shininess="0.7"/>
+    <material name="mat_neck_frost" rgba="0.85 0.88 0.92 1.0" specular="0.4" shininess="0.5"/>
+    <material name="mat_thread" rgba="0.70 0.74 0.80 1.0" specular="0.5" shininess="0.55"/>
+    <material name="mat_cap_white" rgba="0.94 0.94 0.94 1.0" specular="0.35" shininess="0.45"/>
+    <material name="mat_label_orange" rgba="0.93 0.42 0.12 1.0" specular="0.2" shininess="0.3"/>
+    <material name="mat_label_light" rgba="0.93 0.90 0.85 0.9" specular="0.2" shininess="0.3"/>
+  </asset>
+  <worldbody>
+    <body name="bottle">
+      <!-- collision (hidden group 3) -->
+      <geom name="shot_body_col" type="cylinder" size="0.019 0.026" pos="0 0 0.026" group="3"
+            density="220" friction="2.0 0.1 0.005" priority="2" rgba="0.2 0.2 0.2 0"/>
+      <geom name="shot_neck_col" type="cylinder" size="0.0125 0.0075" pos="0 0 0.0595" group="3"
+            density="800" friction="2.0 0.1 0.005" priority="2" rgba="0.2 0.2 0.2 0"/>
+      <geom name="shot_flange_col" type="cylinder" size="0.0165 0.001" pos="0 0 0.0665" group="3"
+            density="800" friction="2.0 0.1 0.005" priority="2" rgba="0.2 0.2 0.2 0"/>
+      <geom name="shot_topneck_col" type="cylinder" size="0.0122 0.0075" pos="0 0 0.0745" group="3"
+            density="600" friction="2.0 0.1 0.005" priority="2" rgba="0.2 0.2 0.2 0"/>
+      <!-- visual -->
+      <geom name="shot_juice_vis" type="cylinder" size="0.0163 0.0225" pos="0 0 0.0275"
+            material="mat_juice" contype="0" conaffinity="0" group="1" density="1000"/>
+      <geom name="shot_label_top_vis" type="cylinder" size="0.0192 0.010" pos="0 0 0.040"
+            material="mat_label_orange" contype="0" conaffinity="0" group="1" density="50"/>
+      <geom name="shot_label_mid_vis" type="cylinder" size="0.0192 0.0065" pos="0 0 0.0235"
+            material="mat_label_light" contype="0" conaffinity="0" group="1" density="50"/>
+      <geom name="shot_label_bot_vis" type="cylinder" size="0.0192 0.0055" pos="0 0 0.0115"
+            material="mat_label_orange" contype="0" conaffinity="0" group="1" density="50"/>
+      <geom name="shot_body_vis" type="mesh" mesh="shot_body_mesh" material="mat_pet"
+            contype="0" conaffinity="0" group="1" density="40"/>
+      <geom name="shot_neck_vis" type="mesh" mesh="shot_neck_mesh" material="mat_neck_frost"
+            contype="0" conaffinity="0" group="1" density="100"/>
+      <geom name="shot_thread_vis" type="mesh" mesh="shot_thread_mesh" material="mat_thread"
+            contype="0" conaffinity="0" group="1" density="100"/>
+      <body name="cap" pos="0 0 0.069">
+        <!-- slide FIRST (overlay contract — see header) -->
+        <!-- The high slide armature models the fine screw's TRANSLATIONAL
+             REFLECTED INERTIA (I_twist / pitch² ≈ 440 kg-equivalent for this
+             thread — 1.0 is conservative): a yank meets thread mechanical
+             advantage inertially, and gravity settle tightens 0.10 → 0.003 mm.
+             It does NOT fix the equality's elastic leak under load — that
+             lever is the equality solimp (measured; see the equality comment).
+             Twist-side cost is negligible (armature · pitch² ≈ 2e-7 kg·m²). -->
+        <joint name="cap_slide" type="slide" axis="0 0 1" range="0 0.008"
+               damping="0.2" armature="1.0"/>
+        <joint name="cap_twist" type="hinge" axis="0 0 1" range="0 16.7552"
+               frictionloss="0.02" damping="0.005" armature="0.0001" solreffriction="0.004 1"/>
+        <geom name="shot_cap_col" type="cylinder" size="0.0145 0.00775" pos="0 0 0.00775" group="3"
+              density="800" friction="2.0 0.1 0.005" priority="2" rgba="0.2 0.2 0.2 0"/>
+        <geom name="shot_cap_vis" type="mesh" mesh="shot_cap_mesh" material="mat_cap_white"
+              contype="0" conaffinity="0" group="1" density="100"/>
+      </body>
+    </body>
+  </worldbody>
+  <contact>
+    <exclude body1="bottle" body2="cap"/>
+  </contact>
+  <equality>
+    <!-- The fine screw: cap_slide = 0.000477465 * cap_twist (3 mm per 2π turn). -->
+    <!-- solimp is deliberately extreme: with a 10 g cap and the solref
+         timeconst floored at 2*dt, the equality's REGULARIZATION (efc_R,
+         set by 1-impedance) is what a pull deflects against — measured, a
+         20 N pull "opened" 3.2 mm at the bottle_cap-style 0.99 impedance
+         with the thread friction NOT slipping. 0.999/0.9999 brings that
+         elastic leak to 0.45 mm while twist-opening is unaffected. -->
+    <joint joint1="cap_slide" joint2="cap_twist" polycoef="0 0.000477465 0 0 0"
+           solref="0.004 1" solimp="0.999 0.9999 0.0005"/>
+  </equality>
+</mujoco>

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