How to avoid slipping with mujoco menagerie's robotiq_2f85 gripper?

[RajGhugare19]

Intro

Hi!

I am a graduate student at Princeton University, I use MuJoCo for my research on reinforcement learning.

My setup

I am using MuJoCo (3.3.3) with Python (3.10.16) on Ubuntu 22.04.

My question

I am using mujoco menagerie's robotiq_2f85 gripper to grip a cube. The gripper is a standalone (without a robot) and it is controlled using position actuators for x,y,z and yaw. I am able to pick the cube stably (after tuning things like friction, mass, and solref). But after picking the cube, if I change to yaw of the gripper the cube slips and drops. The behavior improves after reducing simulation timestep from 0.005 to 0.002. But it still persists if I change the yaw too quickly (videos attached).

What I would like is to keep the timestep as high as possible (so that the simulator is fast for RL training), and reduce this behavior as much as possible.

I have read the tutorial for avoiding slip (https://mujoco.readthedocs.io/en/latest/modeling.html#preventing-slip) and read many issues related to this but haven't been able to solve this issue. I would appreciate any pointers!

Minimal model and/or code that explain my question

Please port the assets from mujoco menagerie and store them in the same parent folder. I am attaching the zip for assets here - assets.zip

Model:

minimal XML

<<mujoco model="scene">
  <compiler angle="radian" meshdir="assets/"/>

  <option impratio="10" integrator="implicitfast" cone="elliptic"/>

  <visual>
    <headlight diffuse="0.9 0.9 0.9" specular="0 0 0"/>
    <scale forcewidth="0.05" contactwidth="0.075" contactheight="0.025" com="0.05" framelength="0.2" framewidth="0.01"/>
  </visual>

  <statistic extent="1.2" center="0.4 0 0.4"/>

  <default>
    <default class="2f85">
      <mesh scale="0.001 0.001 0.001"/>
      <general biastype="affine"/>
      <default class="driver">
        <joint solreflimit="0.005" solimplimit="0.95 0.99" range="0 0.8" armature="0.005" damping="0.1"/>
      </default>
      <default class="follower">
        <joint solreflimit="0.005" solimplimit="0.95 0.99" range="-0.872664 0.872664" armature="0.001"/>
      </default>
      <default class="spring_link">
        <joint springref="2.62" stiffness="0.05" range="-0.296706 0.8" armature="0.001" damping="0.00125"/>
      </default>
      <default class="coupler">
        <joint solreflimit="0.005" solimplimit="0.95 0.99" range="-1.57 0" armature="0.001"/>
      </default>
      <default class="visual">
        <geom type="mesh" contype="0" conaffinity="0" group="2"/>
      </default>
      <default class="collision">
        <geom type="mesh" group="3"/>
        <default class="pad_box1">
          <geom size="0.011 0.004 0.009375" type="box" priority="1" friction="1 0.03 0.003" solref="0.004" solimp="0.95 0.99" rgba="0.55 0.55 0.55 1"/>
        </default>
        <default class="pad_box2">
          <geom size="0.011 0.004 0.009375" type="box" priority="1" friction="1 0.03 0.003" solref="0.004" solimp="0.95 0.99" rgba="0.45 0.45 0.45 1"/>
        </default>
      </default>
    </default>
  </default>

  <asset>
    <texture type="skybox" colorspace="auto" builtin="gradient" mark="random" rgb1="0.05 0.05 0.15" rgb2="0.02 0.02 0.08" markrgb="1 1 1" random="0.005" width="512" height="3072"/>
    <texture type="2d" colorspace="auto" name="groundplane" builtin="checker" mark="cross" rgb1="0.1 0.2 0.3" rgb2="0.1 0.2 0.3" markrgb="0.8 0.8 0.8" width="1024" height="1024"/>
    <material name="metal" rgba="0.58 0.58 0.58 1"/>
    <material name="silicone" rgba="0.1882 0.1882 0.1882 1"/>
    <material name="gray" rgba="0.4627 0.4627 0.4627 1"/>
    <material name="black" rgba="0.149 0.149 0.149 1"/>
    <material name="groundplane" texture="groundplane" texuniform="true" reflectance="0.1"/>
    <mesh name="base_mount" class="2f85" content_type="model/stl" file="base_mount.stl"/>
    <mesh name="base" class="2f85" content_type="model/stl" file="base.stl"/>
    <mesh name="driver" class="2f85" content_type="model/stl" file="driver.stl"/>
    <mesh name="coupler" class="2f85" content_type="model/stl" file="coupler.stl"/>
    <mesh name="follower" class="2f85" content_type="model/stl" file="follower.stl"/>
    <mesh name="pad" class="2f85" content_type="model/stl" file="pad.stl"/>
    <mesh name="silicone_pad" class="2f85" content_type="model/stl" file="silicone_pad.stl"/>
    <mesh name="spring_link" class="2f85" content_type="model/stl" file="spring_link.stl"/>
  </asset>

  <worldbody>
    <geom name="floor" size="1 2 0.01" type="plane" material="groundplane"/>
    <light pos="0 0 1" dir="0 0 -1" type="directional"/>
    <body name="base_mount" childclass="2f85" pos="0 0 0.1" quat="0 0.707107 0.707107 0">
      
      <joint name="arm_tx" pos="0 0 0" axis="0 1 0" type="slide" range="-0.1 1" damping="35.54054032525795"/>
      <joint name="arm_ty" pos="0 0 0" axis="1 0 0" type="slide" range="-0.6 0.6" damping="35.54054032525795"/>
      <joint name="arm_tz" pos="0 0 0" axis="0 0 -1" type="slide" range="0.06 1" damping="35.54054032525795"/>
      <joint name="arm_yaw" pos="0 0 0" axis="0 0 -1" range="-1.5707 1.5707" damping="0.8342708735990816"/>

      <geom class="visual" material="black" mesh="base_mount"/>
      <geom class="collision" mesh="base_mount"/>
      <body name="base" pos="0 0 0.0038" quat="0.707107 0 0 -0.707107">
        <inertial pos="0 -2.70394e-05 0.0354675" quat="0.999999 -0.00152849 0 0" mass="0.777441" diaginertia="0.000260285 0.000225381 0.000152708"/>
        <geom class="visual" material="black" mesh="base"/>
        <geom class="collision" mesh="base"/>
        <site name="pinch" pos="0 0 0.145" group="5" rgba="0.9 0.9 0.9 1"/>
        <body name="right_driver" pos="0 0.0306011 0.054904">
          <inertial pos="2.96931e-12 0.0177547 0.00107314" quat="0.681301 0.732003 0 0" mass="0.00899563" diaginertia="1.72352e-06 1.60906e-06 3.22006e-07"/>
          <joint name="right_driver_joint" class="driver" pos="0 0 0" axis="1 0 0"/>
          <geom class="visual" material="gray" mesh="driver"/>
          <geom class="collision" mesh="driver"/>
          <body name="right_coupler" pos="0 0.0315 -0.0041">
            <inertial pos="0 0.00301209 0.0232175" quat="0.705636 -0.0455904 0.0455904 0.705636" mass="0.0140974" diaginertia="4.16206e-06 3.52216e-06 8.88131e-07"/>
            <joint name="right_coupler_joint" class="coupler" pos="0 0 0" axis="1 0 0"/>
            <geom class="visual" material="black" mesh="coupler"/>
            <geom class="collision" mesh="coupler"/>
          </body>
        </body>
        <body name="right_spring_link" pos="0 0.0132 0.0609">
          <inertial pos="-8.65005e-09 0.0181624 0.0212658" quat="0.663403 -0.244737 0.244737 0.663403" mass="0.0221642" diaginertia="8.96853e-06 6.71733e-06 2.63931e-06"/>
          <joint name="right_spring_link_joint" class="spring_link" pos="0 0 0" axis="1 0 0" springref="2.62"/>
          <geom class="visual" material="black" mesh="spring_link"/>
          <geom class="collision" mesh="spring_link"/>
          <body name="right_follower" pos="0 0.055 0.0375">
            <inertial pos="0 -0.011046 0.0124786" quat="0.986437 0.164143 0 0" mass="0.0125222" diaginertia="2.67415e-06 2.4559e-06 6.02031e-07"/>
            <joint name="right_follower_joint" class="follower" pos="0 -0.018 0.0065" axis="1 0 0"/>
            <geom class="visual" material="black" mesh="follower"/>
            <geom class="collision" mesh="follower"/>
            <body name="right_pad" pos="0 -0.0189 0.01352">
              <inertial pos="0 -0.0025 0.0185" quat="0.707107 0 0 0.707107" mass="0.0035" diaginertia="4.73958e-07 3.64583e-07 1.23958e-07"/>
              <geom name="right_pad1" class="pad_box1" pos="0 -0.0026 0.028125" mass="0"/>
              <geom name="right_pad2" class="pad_box2" pos="0 -0.0026 0.009375" mass="0"/>
              <geom class="visual" mesh="pad"/>
              <body name="right_silicone_pad">
                <geom class="visual" material="black" mesh="silicone_pad"/>
              </body>
            </body>
          </body>
        </body>
        <body name="left_driver" pos="0 -0.0306011 0.054904" quat="0 0 0 1">
          <inertial pos="0 0.0177547 0.00107314" quat="0.681301 0.732003 0 0" mass="0.00899563" diaginertia="1.72352e-06 1.60906e-06 3.22006e-07"/>
          <joint name="left_driver_joint" class="driver" pos="0 0 0" axis="1 0 0"/>
          <geom class="visual" material="gray" mesh="driver"/>
          <geom class="collision" mesh="driver"/>
          <body name="left_coupler" pos="0 0.0315 -0.0041">
            <inertial pos="0 0.00301209 0.0232175" quat="0.705636 -0.0455904 0.0455904 0.705636" mass="0.0140974" diaginertia="4.16206e-06 3.52216e-06 8.88131e-07"/>
            <joint name="left_coupler_joint" class="coupler" pos="0 0 0" axis="1 0 0"/>
            <geom class="visual" material="black" mesh="coupler"/>
            <geom class="collision" mesh="coupler"/>
          </body>
        </body>
        <body name="left_spring_link" pos="0 -0.0132 0.0609" quat="0 0 0 1">
          <inertial pos="-8.65005e-09 0.0181624 0.0212658" quat="0.663403 -0.244737 0.244737 0.663403" mass="0.0221642" diaginertia="8.96853e-06 6.71733e-06 2.63931e-06"/>
          <joint name="left_spring_link_joint" class="spring_link" pos="0 0 0" axis="1 0 0" springref="2.62"/>
          <geom class="visual" material="black" mesh="spring_link"/>
          <geom class="collision" mesh="spring_link"/>
          <body name="left_follower" pos="0 0.055 0.0375">
            <inertial pos="0 -0.011046 0.0124786" quat="0.986437 0.164143 0 0" mass="0.0125222" diaginertia="2.67415e-06 2.4559e-06 6.02031e-07"/>
            <joint name="left_follower_joint" class="follower" pos="0 -0.018 0.0065" axis="1 0 0"/>
            <geom class="visual" material="black" mesh="follower"/>
            <geom class="collision" mesh="follower"/>
            <body name="left_pad" pos="0 -0.0189 0.01352">
              <inertial pos="0 -0.0025 0.0185" quat="0.707107 0 0 0.707107" mass="0.0035" diaginertia="4.73958e-07 3.64583e-07 1.23958e-07"/>
              <geom name="left_pad1" class="pad_box1" pos="0 -0.0026 0.028125" mass="0"/>
              <geom name="left_pad2" class="pad_box2" pos="0 -0.0026 0.009375" mass="0"/>
              <geom class="visual" mesh="pad"/>
              <body name="left_silicone_pad">
                <geom class="visual" material="black" mesh="silicone_pad"/>
              </body>
            </body>
          </body>
        </body>
      </body>
    </body>
    <body name="block_0">
      <joint name="block_joint_0" type="free" limited="false" actuatorfrclimited="false"/>
      <geom name="block_0" size="0.02 0.02 0.02" type="box" contype="3" friction="1 0.03 0.003" solref="0.004" density="1240" rgba="1 0.49 0.43 1"/>
    </body>
  </worldbody>

  <contact>
    <exclude body1="base" body2="right_driver"/>
    <exclude body1="base" body2="right_spring_link"/>
    <exclude body1="base" body2="left_driver"/>
    <exclude body1="base" body2="left_spring_link"/>
    <exclude body1="right_coupler" body2="right_follower"/>
    <exclude body1="left_coupler" body2="left_follower"/>
  </contact>

  <equality>
    <connect body1="right_follower" body2="right_coupler" anchor="0 0 0" solref="0.005" solimp="0.95 0.99"/>
    <connect body1="left_follower" body2="left_coupler" anchor="0 0 0" solref="0.005" solimp="0.95 0.99"/>
    <joint joint1="right_driver_joint" joint2="left_driver_joint" polycoef="0 1 0 0 0" solref="0.005" solimp="0.95 0.99"/>
  </equality>

  <tendon>
    <fixed name="split">
      <joint joint="right_driver_joint" coef="0.5"/>
      <joint joint="left_driver_joint" coef="0.5"/>
    </fixed>
  </tendon>

  <actuator>
    <general name="fingers_actuator" class="2f85" tendon="split" ctrlrange="0 255" forcerange="-5 5" gainprm="0.313725" biasprm="0 -100 -10"/>
    <general name="arm_tx" joint="arm_tx" ctrlrange="-0.1 1" biastype="affine" gainprm="300" biasprm="0 -300"/>
    <general name="arm_ty" joint="arm_ty" ctrlrange="-0.6 0.6" biastype="affine" gainprm="300" biasprm="0 -300"/>
    <general name="arm_tz" joint="arm_tz" ctrlrange="0.06 1" biastype="affine" gainprm="300" biasprm="0 -300"/>
    <general name="arm_yaw" joint="arm_yaw" ctrlrange="-1.5707 1.5707" biastype="affine" gainprm="300" biasprm="0 -300"/>
  </actuator>

  <keyframe>
    <key name="start_pose"
        qpos="-0.001 2.9e-08 0.24 -1.1e-07 0.46 -0.0026 0.45 -0.45 0.46 -0.0026 0.45 -0.45 -2.1e-06 -7.8e-07 0.19 1.0 3.9e-05 0.00042 -0.00028"
        ctrl="200 -0.001 0.0 0.28 0.0"/>
  </keyframe>

</mujoco>

Code:

from mujoco import viewer

sim_dt = 0.002
ctrl_dt = 0.02

xml_path = "slip-debug.xml"
model = mj.MjModel.from_xml_path(xml_path)
model.opt.timestep = sim_dt
data = mj.MjData(model)

mj.mj_resetDataKeyframe(model, data, 0)
mj.mj_forward( model, data )
mj.mj_step( model, data, nstep=int(ctrl_dt / sim_dt))

with viewer.launch_passive(model, data) as v:    
    v.cam.lookat = [0.4, 0.0 , 0.4]
    v.cam.distance = 1.2
    v.cam.azimuth = 180
    v.cam.elevation = -30.0

    while v.is_running():
        mj.mj_step( model, data, nstep=int(ctrl_dt / sim_dt))
        v.sync()

Video for timestep 0.002: https://github.com/user-attachments/assets/49407481-e361-49b6-9bf3-9038696ada1e
Video for timestep 0.005: https://github.com/user-attachments/assets/30e391f8-e6bd-4f80-bc24-5d5657328707

Confirmations

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