RG6 Implementation #2418

adawne · 2025-02-10T16:41:47Z

adawne
Feb 10, 2025

Intro

Hi!

I am using MuJoCo for my research on manipulator.

My setup

MuJoCo 3.2.0, Python 3.11.10

My question

Hi everyone!

I’m working on implementing the RG6 Gripper in MuJoCo, based on this repository:
https://github.com/Zhengxuez/rg6_gripper_description/tree/main

My current issue is that both r_out and r_inner need to connect to r_tip, but MuJoCo doesn’t allow a single body (r_tip) to have two parent bodies.

To work around this, I used an <equality connect> constraint to link r_tip with both r_out and r_inner. This partially works, but the gripper no longer opens/closes fully (see screenshot). When I move r_out_ctrl and l_out_ctrl, the connection between the tips (r_tip and l_tip) seems to break or lock up.

Does anyone have suggestions on how to correctly implement this connection while allowing the gripper fingers to fully open/close? Any tips on alternative constraints, dummy bodies, or joint setups would be greatly appreciated!

Screenshots:

Model image: https://github.com/user-attachments/assets/dff202f7-fafa-4226-ae83-12e0c24d53b8
Partial opening screenshot: https://github.com/user-attachments/assets/28fe9f54-57c8-4b7f-a2d0-e68327ea8692

Thank you!

Minimal model and/or code that explain my question

<body name="base_link" pos="0.00000000 0.00000000 0.00000000" quat="1 0 0 0">
  <freejoint name="floating_base" />
  <geom name="base_link_collision_0" pos="0 0 0" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="base_link.stl" rgba="0 0 0 0" />
  <geom name="base_link_visual" pos="0 0 0" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="base_link.stl" />
  <body name="g_main" pos="-0.031849 1e-06 0.04953" quat="1.0 0.0 0.0 0.0">
    <inertial pos="0.031843851343412694 -6.562152034605188e-05 0.0402561266087614" quat="1.0 0.0 0.0 0.0" mass="2.1746665575894286" diaginertia="0.003297 0.00361 0.00105" />
    <geom name="g_main_collision_0" pos="0.031849 -1e-06 -0.04953" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="g_main.stl" rgba="0 0 0 0" />
    <geom name="g_main_visual" pos="0.031849 -1e-06 -0.04953" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="g_main.stl" />
    
    
    
    <body name="l_out" pos="0.0557 0.0128 0.085" quat="1.0 0.0 0.0 0.0">
      <joint name="l_out" type="hinge" range="-0.75 0.610865" axis="-0.0 1.0 0.0" />
      <inertial pos="0.010442859349590227 -0.012799625869821 0.012792983853972317" quat="1.0 0.0 0.0 0.0" mass="0.24195762212403002" diaginertia="0.00011 0.00016 7.6e-05" />
      <geom name="l_out_collision_0" pos="-0.023851 -0.012801 -0.13453" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="l_out.stl" rgba="0 0 0 0" />
      <geom name="l_out_visual" pos="-0.023851 -0.012801 -0.13453" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="l_out.stl" />
      <body name="l_tip" pos="0.047384 -0.0253 0.06442" quat="1.0 0.0 0.0 0.0">
        <joint name="l_tip" type="hinge" range="-0.523599 0.610865" axis="0.0 -1.0 0.0" />
        <inertial pos="-0.01379426979129901 0.012430443916766657 0.03303967984911002" quat="1.0 0.0 0.0 0.0" mass="0.13426652162693567" diaginertia="5.6e-05 5.9e-05 1.3e-05" />
        <geom name="l_tip_collision_0" pos="-0.071235 0.012499 -0.19895" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="l_tip.stl" rgba="0 0 0 0" />
        <geom name="l_tip_visual" pos="-0.071235 0.012499 -0.19895" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="l_tip.stl" />
      </body>
    </body>




    <body name="r_out" pos="0.0081 0.0128 0.085" quat="1.0 0.0 0.0 0.0">
      <joint name="r_out" type="hinge" range="-0.610865 0.523599" axis="0.0 1.0 0.0" armature="0.005" damping="0.1" solimplimit="0.95 0.99 0.001" solreflimit="0.005 1"/>
      <inertial pos="-0.010522665986501832 -0.012799489922871823 0.012809246687502496" quat="1.0 0.0 0.0 0.0" mass="0.24195762035711757" diaginertia="0.00011 0.00016 7.6e-05" />
      <geom name="r_out_collision_0" pos="0.023749 -0.012801 -0.13453" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="r_out.stl" rgba="0 0 0 0" />
      <geom name="r_out_visual" pos="0.023749 -0.012801 -0.13453" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="r_out.stl" />
      <body name="r_tip" pos="-0.047384 -0.0253 0.064494" quat="1.0 0.0 0.0 0.0">
        <joint name="r_tip" type="hinge" range="-0.610865 0.523599" axis="0.0 -1.0 0.0" />
        <inertial pos="0.01379460286375201 0.012599371946431372 0.03303919214417522" quat="1.0 0.0 0.0 0.0" mass="0.13426652162693592" diaginertia="5.6e-05 5.9e-05 1.3e-05" />
        <geom name="r_tip_collision_0" pos="0.071133 0.012499 -0.199024" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="r_tip.stl" rgba="0 0 0 0" />
        <geom name="r_tip_visual" pos="0.071133 0.012499 -0.199024" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="r_tip.stl" />
      </body>
    </body>


    <body name="l_inner" pos="0.0424 0.0001 0.1081" quat="1.0 0.0 0.0 0.0">
      <joint name="l_passive" type="hinge" range="-0.610865 0.523599" axis="0.0 -1.0 0.0" />
      <inertial pos="0.021220873634115123 -0.00019955790008889003 0.02884270588361451" quat="1.0 0.0 0.0 0.0" mass="0.0502402669834145" diaginertia="3.4e-05 4.6e-05 2e-05" />
      <geom name="l_inner_collision_0" pos="-0.010551 -0.000101 -0.15763" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="l_inner.stl" rgba="0 0 0 0" />
      <geom name="l_inner_visual" pos="-0.010551 -0.000101 -0.15763" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="l_inner.stl" />
    </body>
    <body name="r_inner" pos="0.0214 0.0001 0.1081" quat="1.0 0.0 0.0 0.0">
      <joint name="r_passive" type="hinge" range="-0.610865 0.523599" axis="-0.0 1.0 -0.0" armature="0.005" damping="0.1" solimplimit="0.95 0.99 0.001" solreflimit="0.005 1"/>
      <inertial pos="-0.021275767636285234 -0.00019955790008339296 0.02887567083082221" quat="1.0 0.0 0.0 0.0" mass="0.05024026698344974" diaginertia="3.4e-05 4.6e-05 2e-05" />
      <geom name="r_inner_collision_0" pos="0.010449 -0.000101 -0.15763" quat="1.0 0.0 0.0 0.0" type="mesh" mesh="r_inner.stl" rgba="0 0 0 0" />
      <geom name="r_inner_visual" pos="0.010449 -0.000101 -0.15763" quat="1.0 0.0 0.0 0.0" material="default_material" type="mesh" mesh="r_inner.stl" />
    </body>
    <body name="hand_tcp" pos="0.036 0 0.21" quat="1.0 0.0 0.0 0.0" />
  </body>
  <site name="base_link_site" pos="0 0 0" quat="1 0 0 0" />
</body>

<equality>
  <connect anchor="0 0 0" body1="r_tip" body2="r_inner" solimp="0.95 0.99 0.001" solref="0.005 1"/>
  <connect anchor="0 0 0" body1="l_tip" body2="l_inner" solimp="0.95 0.99 0.001" solref="0.005 1"/>
  <!-- <joint joint1="r_out" joint2="r_passive"/> -->
</equality>

<contact>
  <exclude body1="base_link" body2="r_inner"/>
  <exclude body1="base_link" body2="r_out"/>
  <exclude body1="r_out" body2="r_tip"/>
  <exclude body1="r_inner" body2="r_tip"/>

  <exclude body1="base_link" body2="l_inner"/>
  <exclude body1="base_link" body2="l_out"/>
  <exclude body1="l_out" body2="l_tip"/>
  <exclude body1="l_inner" body2="l_tip"/>
</contact>

<actuator>
  <position name="l_out_ctrl" joint="l_out" forcerange="-100.00000000 100.00000000" forcelimited="true" ctrlrange="-0.75 0.610865" ctrllimited="true" />
  <position name="l_tip_ctrl" joint="l_tip" forcerange="-100.00000000 100.00000000" forcelimited="true" ctrlrange="-0.523599 0.610865" ctrllimited="true" />
  <position name="r_out_ctrl" joint="r_out" forcerange="-100.00000000 100.00000000" forcelimited="true" ctrlrange="-0.610865 0.523599" ctrllimited="true" />
  <position name="r_tip_ctrl" joint="r_tip" forcerange="-100.00000000 100.00000000" forcelimited="true" ctrlrange="-0.610865 0.523599" ctrllimited="true" />
  <position name="l_passive_ctrl" joint="l_passive" forcerange="-100.00000000 100.00000000" forcelimited="true" ctrlrange="-0.610865 0.523599" ctrllimited="true" />
  <position name="r_passive_ctrl" joint="r_passive" forcerange="-100.00000000 100.00000000" forcelimited="true" ctrlrange="-0.610865 0.523599" ctrllimited="true" />
</actuator>

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 · 2025-02-12T13:58:03Z

yuvaltassa
Feb 12, 2025
Maintainer

The Menagerie has a similar gripper, maybe take inspiration?

0 replies

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RG6 Implementation #2418

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RG6 Implementation #2418

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adawne Feb 10, 2025

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 1 comment

Uh oh!

yuvaltassa Feb 12, 2025 Maintainer

adawne
Feb 10, 2025

yuvaltassa
Feb 12, 2025
Maintainer