mujoco

# Cards

Playing-card models, sharing the card mesh and face textures in [`assets`](assets).

<p float="left">
  <a href="https://live.mujoco.org/?model=github:google-deepmind/mujoco/main/model/cards/cards.xml" title="Open in live.mujoco.org"><img src="https://www.gstatic.com/mujoco/model/cards/cards.png" width="49%"></a>
  <a href="https://live.mujoco.org/?model=github:google-deepmind/mujoco/main/model/cards/house_of_cards.xml" title="Open in live.mujoco.org"><img src="https://www.gstatic.com/mujoco/model/cards/house_of_cards.png" width="49%"></a>
</p>

Click an image to open the model in the browser viewer at [live.mujoco.org](https://live.mujoco.org).

| Model | Description |
| --- | --- |
| [`cards.xml`](cards.xml) | A deck of loose cards. |
| [`house_of_cards.xml`](house_of_cards.xml) | A 26-card, four-storey house. |

The house stands on friction alone, and stays standing: settled, it drifts by about a millimetre
over two minutes of simulated time. Cards are 0.7 mm thick, so the contacts are the awkward kind —
nearly parallel faces meeting at shallow angles, where a collider has the least information to work
with. Two details carry the model:

* **Collision cards are a thin box at the card's true footprint, with over-damped contacts.**
  Contacts between 0.7 mm boxes ring at critical damping, and the ringing eventually topples the
  apex pair; `dampratio` 3 removes it and lets the house run at 2 ms. The visual card is a
  separate, non-colliding mesh.
* **Every card carries a baked-in yaw of a few tenths of a degree, and a fraction of a millimetre
  of jitter along the ridges.** Exactly symmetric, perfectly aligned stacks are adversarial for a
  collider: the pristine arrangement is the one that falls over.

Frictional stacking of this kind requires `cone="elliptic"` and a large `impratio`. Adding
`noslip_iterations` cuts the residual creep further, at some cost in speed; see the comments in
the file.

## Changelog

* 07-09-2026: Added `house_of_cards.xml`.