Unstable hydroelastic cube contact

[amcastro-tri]

What happened?

This was first reported internally by @AdityaBhat-TRI when manipulating a cube in simulation.
Here I provide a minimum reproduction with a cube on top of the ground. The cube has 10 cm sides and it has a 1 kg mass.

We observe rattling with either zero margin or the recommended 1e-4 m margin.
Increasing margin to a large value of 1 cm should remove any rattling. Rattling is removed, however we observe the box leaning towards one of its corners. This is most unexpected.

Finally, @joemasterjohn observed that if we perturbe one of the lenghts of the cubes by something as small as 1e-4m, the problem goes away. Also most unexpected. The problem seems to be for perfect or close to perfect cubes?

Version

1.35.0

[jbinagia]

Just to add some additional data points, I also am observing this (I believe same) issue, reproduced in deepnote here. Some notes:

• In my case, I also observe the rattling for non-cubes (general cuboids)
• I do not observe the rattling anymore if I switch discrete_contact_approximation to sap (as opposed to lagged or similar)