Using force sensors to measure the force on a body within a flexcomp?

[kurtenkera]

Intro

Hi!

I'm using MuJoCo for soft robotics research.

My setup

I am on the latest version of MuJoCo, using the Python API on a Linux machine with Ubuntu 22.04.

My question

I have a soft gripper model which I've talked about in a previous post. I would like to measure the force acting on a single node/body within say the left soft gripper finger. The documentation says that when choosing the site for a force sensor:

The convention is that the site is attached to the child body, and the force points from the child towards the parent.

But how would one do this for the case of a body within a flexcomp? For example, in the code below, a number of bodies (equal to the number of vertices in leftfinger.msh) are automatically created. How can I place a site at a particular body to measure the force acting on that body throughout a simulation?

<flexcomp name="left" euler = "90 0 45" type="gmsh" file="leftfinger.msh" dim="3" 
		        pos="-0.090 0.015 0.033" radius="0.001" rgba="1 1 1 1" mass="4" dof = "full">
		<contact condim="3" solref="0.03 1" solimp=".95 .99 .0001" selfcollide="none" internal = "true"/>
		<elasticity young="5e5" damping="0.003" poisson="0.2"/>
</flexcomp>

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, you can save and load the file so that the flexcomp will be expanded into the bodies that form it and a new deformable section will be created with the list of bodies that form the flex.