How to properly work with meshes in Mujoco?

[JDRanpariya]

Intro

Hi!

I am a graduate student at FAU, I use MuJoCo for my research on Domain Randomization and Reinforcement learning simulation.

My setup

Python 3.9
Mujoco 3.3.1
WSL2 Ubuntu

My question

I'm working with a linear control system consisting of cart on a platform which can move in 1 direciton and has ball on top which can roll freely. I want to create accurate simulation of my system using Mujoco which then I want to be able to change few physical parameters and even the shape of cart to make my reinforcement model more robust to real world situation.

Currently I've created .stl files for 3 components ball, cart and platform, I'm loading it via xml(MJCF) but I'm getting weird behaviour when I run simulate. I've attached the meshes and mjcf for reference.

I'm not sure how to interpret the convex hulls or collision visulization that we get from simulate. On seeing the MJCF in Mujoco Simulate it starts duplicating the cart and ball in x direction. I expect it the ball if little bit in air to fall on cart and then when I move my cart through control it should go left or right but it's stuck and doesn't move. Is it due to meshes being exported from blender? how do I fix that, if it's a scaling issue?

I might have missed related issues/discussions, please point me to them if they are relevent. I'm pretty new to this so thanks for your patience.

mujoco_test.zip

Minimal model and/or code that explain my question

No response

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