Robot penetrate the terrain or get stuck in gaps

[zitongbai]

Intro

Hi!

I am a graduate student, I use MuJoCo for my research on legged robot.

My setup

MuJoCo version 3.2.6

My question

I simulated robot walking on the terrain created by geoms (like <geom pos="8.2 0.0 0.15" type="box" size="0.1 0.75 0.15" quat="1.0 0.0 0.0 0.0" />). But I found that robot's leg may penetrate through the geom and it would be stuck in the gap between geoms and ground or between two geoms. Is there any method to resolve this phenomenon?

Thanks for your attention and help in advance.

Minimal model and/or code that explain my question

Model:

<mujoco model="go2 scene">
  <include file="go2.xml" />

  <statistic center="0 0 0.1" extent="0.8" />

  <visual>
    <headlight diffuse="0.6 0.6 0.6" ambient="0.3 0.3 0.3" specular="0 0 0" />
    <rgba haze="0.15 0.25 0.35 1" />
    <global azimuth="-130" elevation="-20" />
  </visual>

  <asset>
    <texture type="skybox" builtin="gradient" rgb1="0.3 0.5 0.7" rgb2="0 0 0" width="512"
      height="3072" />
    <texture type="2d" name="groundplane" builtin="checker" mark="edge" rgb1="0.2 0.3 0.4"
      rgb2="0.1 0.2 0.3" markrgb="0.8 0.8 0.8" width="300" height="300" />
    <material name="groundplane" texture="groundplane" texuniform="true" texrepeat="5 5"
      reflectance="0.2" />
    <hfield name="perlin_hfield" size="1.0 0.75 0.2 0.2" file="../height_field.png" />
    <hfield name="image_hfield" size="1.0 1.0 0.02 0.1" file="../unitree_hfield.png" />
  </asset>

  <worldbody>
    <light pos="0 0 1.5" dir="0 0 -1" directional="true" />
    <geom name="floor" size="0 0 0.05" type="plane" material="groundplane" />
    <geom pos="2.0 0.0 0.4" type="box" size="1.5 0.75 0.05"
      quat="0.984807753012208 0.0 -0.17364817766693033 0.0" />
    <geom pos="4.78 0.0 0.4" type="box" size="1.5 0.75 0.05"
      quat="0.984807753012208 0.0 0.17364817766693033 0.0" />
    <geom pos="7.2 0.0 0.025" type="box" size="0.10500000000000001 0.75 0.025"
      quat="1.0 0.0 0.0 0.0" />
    <geom pos="7.4 0.0 0.05" type="box" size="0.10500000000000001 0.75 0.05" quat="1.0 0.0 0.0 0.0" />
    <geom pos="7.6 0.0 0.07500000000000001" type="box"
      size="0.10500000000000001 0.75 0.07500000000000001" quat="1.0 0.0 0.0 0.0" />

<!-- something else -->

  </worldbody>
</mujoco>

Detailed model file can be found here

Confirmations

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

[yuvaltassa]

The easiest solution is to make the static geoms overlap.

[zitongbai]

Thanks for your suggestion, I will take a try.

[zitongbai]

It do work, but I'm curious if there are more sophisticated approaches available. Could you recommend some documentation for further reference?

[yuvaltassa]

You could add collision margins. Search for "margin" in the docs. But margins are invisible so are usually not what you want.