Building a cable with MjSpecs

[vmstavens]

Intro

Hi!

I am a Ph.d student, and I use MuJoCo for my research on manipulation of deformable object, specifically deformable linear objects. I am a happy user of MuJoCo and have a quick question.

My setup

My Setup:
Ubuntu 24.04
mujoco 3.3.5

My question

How can i use MuJoCo Specs (MjSpecs) to make a cable like I would in mjcf (from here)? :

<extension>
   <plugin plugin="mujoco.elasticity.cable"/>
</extension>

<worldbody>
   <composite prefix="actuated" type="cable" curve="cos(s) sin(s) s" count="41 1 1"
              size="0.25 .1 4" offset="0.25 0 .05" initial="none">
      <plugin plugin="mujoco.elasticity.cable">
         <!--Units are in Pa (SI)-->
         <config key="twist" value="5e8"/>
         <config key="bend" value="15e8"/>
         <config key="vmax" value="0"/>
      </plugin>
      <joint kind="main" damping="0.15" armature="0.01"/>
      <geom type="capsule" size=".005" rgba=".8 .2 .1 1"/>
   </composite>
</worldbody>

Minimal model and/or code that explain my question

No response

Confirmations

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

[quagla]

Hi, despite the fact that I am the author of both the cable and mjSpec, unfortunately there is no easy way to combine the two. But I do see your point, it would be good to have a helper function in mjSpec. A workaround is to create an mjSpec by parsing an XML string that contains the cable (like in the model you pasted), and then edit that mjSpec or attach it to your more complex scene.

[vmstavens]

Awesome, thank you so much for getting back to me so fast! It is nice to hear that my confusion is justified, coming from the individual actively working on it :) Your solution sounds great. Perhaps a function could generate a temporary cable.xml file in the ".cache" directory, similar to the mujoco_menagerie models we obtain from robot_descriptions from PyPi. The XML would then be customizable from the function API. I will try this out, thanks! :)