How interconnect things properly #2507

alicefasoli · 2025-03-17T16:02:30Z

alicefasoli
Mar 17, 2025

Intro

Hi!

I am a young researcher, I use MuJoCo for my research on robotics application.

My setup

My setup is python version of Mujoco on ubuntu 22.04

My question

I am trying to simulate my gripper which is an OnRobot RG2. The simulation seems good but I am not able to interconnect properly the things more in specific I want to connect rg2_r_truss_arm_link with rg2_r_finger_link (same for the other finger) but I don't understand how.

Thanks for help.

<mujoco model="rg2">
  <compiler angle="radian" />

  <asset>
    <mesh name="quick_changer" file="meshes/rg2/quick_changer.stl" />
    <mesh name="hand" file="meshes/rg2/hand.stl" />
    <mesh name="moment_arm" file="meshes/rg2/moment_arm.stl" />
    <mesh name="finger" file="meshes/rg2/finger.stl" />
    <mesh name="truss_arm" file="meshes/rg2/truss_arm.stl" />
  </asset>

  <worldbody>
    <body name="quick_changer_link">
      <geom pos="0 0 0.015" quat="0 0 0.707107 -0.707107" type="mesh" mesh="quick_changer" />
      <body name="rg2_base_link" pos="0 0 0.015" quat="0.5 -0.5 -0.5 -0.5">
        <inertial pos="0.061902 0.000129 -5e-06" quat="-0.00161435 0.707105 -0.00161435 0.707105" mass="1.68456" diaginertia="0.00262 0.002401 0.000862" />
        <geom type="mesh" mesh="hand" />
        <body name="rg2_l_moment_arm_link" pos="0.105 0.017 0.01">
          <inertial pos="0.017004 0.006397 -0.0103" quat="0.116079 0.697514 -0.116079 0.697514" mass="0.160209" diaginertia="8.3e-05 7.8504e-05 1.6496e-05" />
          <joint name="rg2_gripper_joint" pos="0 0 0" axis="0 0 1" range="-0.45 1" actuatorfrcrange="-10.6 10.6" damping="0.1" />
          <geom type="mesh" mesh="moment_arm" />
          <body name="rg2_l_finger_link" pos="0.049 0.026 0">
            <inertial pos="0.024695 -0.010178 -0.010001" quat="0.435925 0.435925 0.556749 0.556749" mass="0.081638" diaginertia="2.62355e-05 2.6e-05 4.76454e-06" />
            <joint name="rg2_l_finger_2_joint" pos="0 0 0" axis="0 0 1" range="-1.5708 1.5708" actuatorfrcrange="-10.6 10.6" damping="0.1" />
            <geom type="mesh" mesh="finger" />
          </body>
        </body>
        <body name="rg2_l_truss_arm_link" pos="0.122 0.008 0.01">
          <inertial pos="0.023075 0.012136 -0.01" quat="0.604527 0.604527 0.366807 0.366807" mass="0.065927" diaginertia="2.92066e-05 2.5e-05 4.79344e-06" />
          <joint name="rg2_l_finger_passive_joint" pos="0 0 0" axis="0 0 1" range="-1.5708 1.5708" actuatorfrcrange="-10.6 10.6" damping="0.1" />
          <geom type="mesh" mesh="truss_arm" />
        </body>
          
        <body name="rg2_r_moment_arm_link" pos="0.105 -0.017 0.01">
          <inertial pos="0.017004 -0.006397 -0.0103" quat="-0.116079 0.697514 0.116079 0.697514" mass="0.160209" diaginertia="8.3e-05 7.8504e-05 1.6496e-05" />
          <joint name="rg2_r_finger_1_joint" pos="0 0 0" axis="0 0 1" range="-1.5708 1.5708" actuatorfrcrange="-10.6 10.6" damping="0.1" />
          <geom pos="0 0 -0.02" quat="0 1 0 0" type="mesh" mesh="moment_arm" />
          <body name="rg2_r_finger_link" pos="0.049 -0.026 0">
            <inertial pos="0.024695 0.010178 -0.01" quat="0.556749 0.556749 0.435925 0.435925" mass="0.081637" diaginertia="2.62355e-05 2.6e-05 4.76454e-06" />
            <joint name="rg2_r_finger_2_joint" pos="0 0 0" axis="0 0 1" range="-1.5708 1.5708" actuatorfrcrange="-10.6 10.6" damping="0.1" />
            <geom pos="0 0 -0.02" quat="0 1 0 0" type="mesh" mesh="finger" />
          </body>
        </body>

        <body name="rg2_r_truss_arm_link" pos="0.122 -0.008 0.01">
          <inertial pos="0.023075 -0.012136 -0.01" quat="0.366807 0.366807 0.604527 0.604527" mass="0.065927" diaginertia="2.92066e-05 2.5e-05 4.79344e-06" />
          <joint name="rg2_r_finger_passive_joint" pos="0 0 0" axis="0 0 1" range="-1.5708 1.5708" actuatorfrcrange="-10.6 10.6" damping="0.1" />
          <geom pos="0 0 -0.02" quat="0 1 0 0" type="mesh" mesh="truss_arm" />
        </body>
      </body>
    </body>
  </worldbody>

  
  <contact>
    <exclude body1="rg2_base_link" body2="rg2_l_moment_arm_link"/>
    <exclude body1="rg2_base_link" body2="rg2_l_truss_arm_link"/>
    <exclude body1="rg2_l_truss_arm_link" body2="rg2_l_finger_link"/>
    <exclude body1="rg2_base_link" body2="rg2_r_moment_arm_link"/>
    <exclude body1="rg2_base_link" body2="rg2_r_truss_arm_link"/>
    <exclude body1="rg2_r_truss_arm_link" body2="rg2_r_finger_link"/>
  </contact>

  <equality>
    <connect anchor="0 0 0" body1="rg2_l_finger_link" body2="rg2_l_truss_arm_link" solimp="0.95 0.99 0.001" solref="0.005 1"/>
    <connect anchor="0 0 0" body1="rg2_r_finger_link" body2="rg2_r_truss_arm_link" solimp="0.95 0.99 0.001" solref="0.005 1"/>
  </equality>
  
</mujoco>

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 · 2025-03-19T02:54:26Z

yuvaltassa
Mar 19, 2025
Maintainer

Are you visualizing your equality constraints? ('E' in simulate)
The site semantic for equality constraints is easier to use ("align site1 and site2")
There are a bunch of models here you might want to look at. Look at models with "equality" or "connect" in the name.

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How interconnect things properly #2507

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alicefasoli Mar 17, 2025

Intro

My setup

My question

Confirmations

Replies: 1 comment

Uh oh!

yuvaltassa Mar 19, 2025 Maintainer

alicefasoli
Mar 17, 2025

yuvaltassa
Mar 19, 2025
Maintainer