Problems with Vertical Drop Simulations

[HoangGiang93]

Intro

Hi!

I am a researcher at Institute for Artificial Intelligence, University of Bremen, I use MuJoCo for my research.

My setup

MuJoCo 3.2.6

My question

MontessoriBox.mp4

I'm working on simulating a Montessori box where I drop six different objects—five primitive shapes—into various drawers. In the simulation, as shown in the video, four objects behave as expected, but the two blue ones do not. Despite adjustments to various parameters, I haven't resolved this issue. Here are my questions:

1. Why do the blue objects fail to drop stably despite being primitive shapes? Shouldn't their behavior be more predictable?
2. The objects in the middle drop correctly, but when I run the simulation slowly, the triangle shifts slightly to the side, causing the drawer to open a bit, even though it's dropped vertically. What could be causing this movement?
3. What steps can I take to correct these issues in the simulation?

Minimal model and/or code that explain my question

montessori_box.zip

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.

[Balint-H]

Interestingly it only happens with the cylinder and box objects. Interestingly, enabling multiccd and nativeccd resolves the penetration issue, and you could use that as a fix for now.

Reducing solref's time constant (the first element) for the collisions also prevents the penetrations (the contacts become stiffer and the objects do not penetrate below the drawer)

[HoangGiang93]

Thank you very much!