How to measure the foce of the cable

[Lu-Weiyan]

Intro

Hi!

I am a student. I use MuJoCo for my research.

My setup

mujoco 3.2.2
Python 3.8.19

My question

Can I use the force sensor to measure the force of cable?As we know,we can't set a site in the cable.But the force sensor need to be set in sites.Are there any examples about it?Now I set a site in the drone.But the sensor only measure the total external force for my drone.Can I measure the force between the cable and my drone?

Minimal model and/or code that explain my question

<composite prefix="A" type="cable" curve="s"  size="0.01" initial="free" vertex="0 0 0.9 0 0 0.868 0 0 0.836 0 0 0.804 0 0 0.772 0 0 0.74 0 0 0.708 0 0 0.676 0 0 0.644 0 0 0.612 0 0 0.58 0 0 0.548 0 0 0.516 0 0 0.484 0 0 0.452 0 0 0.42 0 0 0.388 0 0 0.356 0 0 0.324 0 0 0.292 0 0 0.26  0 0 0.259">
    <plugin plugin="mujoco.elasticity.cable">
          <config key="twist" value="6e5"/>
          <config key="bend" value="1e6"/>
          <config key="vmax" value="1e4"/>
    </plugin>
      <joint kind="main" damping=".015"/>
      <geom type="capsule" size=".005" rgba=".8 .2 .1 1" condim="1"/>
</composite>

Confirmations

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

[Lu-Weiyan]

cf2.md
This is my xml

[quagla]

Hi if you save the XML, the composite will get expanded into bodies, so you can sites to any body where you need a force measurement.

[Lu-Weiyan]

ok,let me have a try

[Lu-Weiyan]

I try it and succeed to add the force sensor for the first part of the cable.And I also add the force sensor for my payload.However,I only get the true force from the sensor of my drone.And others are all close to zero, while my drone is flying .The difference lie in whether there is an actuator or not.Can't the force sensor measure without the external actuator?How can I solve this problem?
myscene.md

[Lu-Weiyan]

The mass of my payload is 0.2kg.While the drone is hovering,the true force of the payload is 0.2*9.81N.However, it is still close to zero.

[Lu-Weiyan]

Can the force measure the external force?For example, the force of the wind?

[Lu-Weiyan]

I find the problem is about the parent-child relationship between bodies,thanking for your answer!