Flexcomp identifying pin IDs #3052

Annie-spaces · 2026-01-26T20:24:11Z

Annie-spaces
Jan 26, 2026

Intro

Hi!

I am an undergraduate at NUS, I use MuJoCo for my research on hybrid robotic simulation.

My setup

MuJoCo 3.0
Python
Windows 11

My question

I am trying to learn how to identify the pin IDs for flexcomp.

I followed the documentation and used show body_labels, but the labels were not zero-based. Instead, they were more coordinated-like. I wonder how we can identify the automatically generated zero-based pin IDs. The image below was a screenshot from running the example "gripper_trilinear.xml"

I have another example with a random mesh object I generated. The body labels were also not zero-based pin IDs.

It's corresponding Mesh file is attached here
Mesh.zip

Minimal model and/or code that explain my question

Model:

minimal XML for a random mesh. The obj file is attached in the zip file above

<mujoco model="Trilinear">

  <include file="scene.xml"/>

  <option solver="CG" tolerance="1e-6" timestep=".001" integrator="implicitfast"/>
    <compiler angle="radian" meshdir="./assets/"/>

  <size memory="100M"/>

  <visual>
    <map stiffness="100"/>
  </visual>

  <worldbody>
    <body>
      <joint name="press" type="slide" axis="0 0 1" damping="500"/>
      <geom type="box" size=".02 .2 .2" pos="0 0 .5"/>
    </body>
    <flexcomp type="mesh" file="Mesh.obj" pos="0 0 0" dim="2" euler="0 0 0"
              radius=".001" rgba="0 .7 .7 1" mass=".05" name="softbody" dof="trilinear" scale="10 10 10">
      <elasticity young="1e5" poisson="0.1" damping="0.001" elastic2d="stretch"/>
      <contact selfcollide="none" internal="false"/>
    </flexcomp>
  </worldbody>

  <actuator>
    <position name="press" joint="press" gear="-1 0 0 0 0 0" ctrlrange="-1 1" kp="1000"/>
  </actuator>
</mujoco>

Code:

import mujoco
import mujoco.viewer as viewer
model = mujoco.MjModel.from_xml_path(   )
data = mujoco.MjData(model)

viewer.launch(model, data)

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Flexcomp identifying pin IDs #3052

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Flexcomp identifying pin IDs #3052

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Annie-spaces Jan 26, 2026

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 0 comments

Annie-spaces
Jan 26, 2026