Skip to content

Known gap: the wrapped present cannot be unwrapped yet

What

  • The reference task set's unwrap-gift task: tear the taped wrapping paper off a present box until the box is free of paper (paper on at most 5 % of the box's surface, the box closed and upright).
  • Alloy has the start state: the library's gift_wrapped_present, a 187 x 132 x 55 mm box wrapped in 82 um kraft wrapping paper (girth wrap with the seam under the box, ends folded; its OBJ carries the flat sheet, so a card can put tear lines on it), placed on its box by alloy.tasks.gift_present.add_present (the wrapped-present measurements in the development notes, not shipped).
  • No task unwraps it: there is no scripted motion that takes the paper off, and no test of one.

Number

  • The task is not run: 0 % of the paper comes off (the reference's gate: paper on at most 5 % of the box).
  • The start state rests: on an NVIDIA L4, 64 worlds x 1 s, the wrap moves at most 1.7 mm and the box tilts at most 0.3 deg, health ok (the wrapped-present measurements in the development notes, not shipped). With tear lines, 25 of 64 worlds lose the rest within 0.2 s (reason 5).
  • The reference task set's own demonstrations did not unwrap it either, even with hands that attach to the paper.

Why

  1. Nothing to take hold of. The paper lies flat on the box. The gantry's fingers and hook (alloy/tasks/gift_gantry.py) pinch or push edges that stand free; the wrap's free edges are the seam's edge, pressed under the box, and the end flaps' edges, lying flat on the stacked end layers. The film's grip (alloy/solvers/film/grip.py) holds a sheet between two jaws, which also have to get round an edge first.
  2. The layers stand 1 mm apart. A film particle collides at 0.5 mm, so every layer stands a pitch of 1 mm off the one below it (12 times the paper's 82 um), and an end stacks up to six layers. No tine or finger fits between two layers to lift a flap, and a thinner contact radius would need a finer clock than the coupling already runs.
  3. Tape. The reference tapes the seam and the ends. WP13's Bonds plug-in bonds film to rigid bodies only; tape on paper needs film-to-film bonds that break by peel, which are not modelled.

  4. Cost. The box on the film couples at the lightest body's clock: about 0.16 ms (j = 6), so a task of tens of seconds is a GPU-only run.

  5. Tear lines do not hold on the folded wrap. Tear lines on the flat sheet build (alloy/solvers/film/layout.py: 390 edges at 44 mm, every vertex copy on the sheet's grid), but with them the present does not rest. On an NVIDIA L4, 64 identical worlds x 0.2 s: 25 lose the rest (the outer layer of an end stack peels out from 0.04 s, the box tips 17 deg by 0.2 s, the film's strain projection unconverged), 39 rest; without tear lines all 64 rest (wrap <= 2.1 mm, box tilt <= 0.4 deg). Which worlds fail follows the VBD colouring: Newton's colour balancing colours identical worlds differently (worlds 41-63 alike). One world on a CPU with world 41's colouring moved 20 mm by 0.08 s and kept going; with world 0's it moved 13 mm at 0.04 s and settled back to 4 mm. So the library card has no tear lines.

Workaround

None for the whole task. For tearing a wrap by hand, use paper_wrap_tear_sheet lying flat with an edge the gripper can pinch (the tear-line measurements in the development notes, not shipped); the wrapped present serves as a resting start state (for looks, perception and contact with the box).

Planned fix

Not scheduled: unwrap-gift was parked on 2026-11-07 for the open-carton task. It needs: - A grasp for a sheet lying on a surface: an attachment-style hold on film particles under a fingertip (as the reference's hands), or a finger that slides under a lifted corner. - Film-to-film tape: breakable bonds between two film layers with a peel law (an extension of the film's seams). - A paper contact radius nearer the sheet's thickness, with the clock it needs. - Seams that hold a folded sheet in every colouring (or one colouring per world), so the wrap can carry tear lines.