Anisotropic friction simulation for differential drive #2926

ThreeTNT · 2025-11-04T09:35:37Z

ThreeTNT
Nov 4, 2025

Intro

Hi!

I am a undergrad student at the University of Waterloo, I use MuJoCo as a simulation tool for my robotics team.

My setup

I'm using MuJoCo 3.3.7 Python API, on Arch Linux.

My question

I'm trying to simulate a type of omni-direction wheel, where there are small rollers along the edge of the wheel allowing it to slide sideways but still retain traction forwards. I figured that this could be simulated via anisotropic fricton, where the friction parallel to the axis is smaller than the forward facing direction. However, Mujoco seems to be computing the anisotropic friction using the global reference frame's axis, not the wheel's frame, resulting in weird behavior.

https://www.youtube.com/watch?v=bMuylooiirg

Ive looked around and saw #67, but I do not know how to make a capsule into a wheel for this application.

Ive also tried to dynamically adjust friction in real time via python, but it ended up being clunky and undesirable (there would be periods of low friction and then high friction, causing weird effects)

Is there any way to simulate anisotropic friction?

Minimal model and/or code that explain my question

<mujoco model="slide box">
  <compiler meshdir="assets" texturedir="assets"/>
  <visual>
    <global offwidth="1920" offheight="1080"/>
  </visual>
  <option integrator="RK4" gravity="0 0 -9.81" timestep="0.001" iterations="100" tolerance="1e-10">
    <flag contact="enable"/>
  </option>
  
  <asset>
    <texture name="grid" type="2d" builtin="checker" rgb1=".1 .2 .3" rgb2=".2 .3 .4" width="512" height="512"/>
    <material name="grid" texture="grid" texrepeat="1 1" texuniform="true" reflectance=".2"/>
  </asset>

  <default>
		<geom contype="1" conaffinity="1"/>
    <equality solimp="0.9950 0.9990 0.0001" solref="0.0100 0.7500"/>
	</default>

  <worldbody>
    <camera name="fixed" pos="0 2 2" mode="targetbody" target="robot"/>

    <light directional="true" diffuse="1 1 1" specular="1 1 1" 
           pos="0 0 10" dir="-1 -1 -1"/>

    <geom name="floor" type="box" 
      size="10 10 1"
      material="grid"/>
    
    <body name="robot" pos="0 0 1.1" euler="0 0 0">
      <geom name="chassis" type="box" size="0.3 0.3 0.05" rgba="0.2 0.2 0.8 1" mass="5"/>

      <freejoint/>
    
      <body name="left_front_wheel" pos="0.25 0.36 0">
        <geom name="lf_wheel" type="cylinder" size="0.1 0.05" rgba="0.5 0.5 0.5 1" 
              mass="0.05" euler="90 0 0" material="grid"/>
        <joint name="left_front_joint" type="hinge" axis="0 1 0" damping="0.01"/>
      </body>
      
      <body name="left_mid_wheel" pos="0 0.36 0">
        <geom name="lm_wheel" type="cylinder" size="0.1 0.05" rgba="0.5 0.5 0.5 1" 
              mass="0.05" euler="90 0 0" material="grid"/>
        <joint name="left_mid_joint" type="hinge" axis="0 1 0" damping="0.01"/>
      </body>
      
      <body name="left_rear_wheel" pos="-0.25 0.36 0">
        <geom name="lr_wheel" type="cylinder" size="0.1 0.05" rgba="0.5 0.5 0.5 1" 
              mass="0.05" euler="90 0 0" material="grid"/>
        <joint name="left_rear_joint" type="hinge" axis="0 1 0" damping="0.01"/>
      </body>
      
      <body name="right_front_wheel" pos="0.25 -0.36 0">
        <geom name="rf_wheel" type="cylinder" size="0.1 0.05" rgba="0.5 0.5 0.5 1" 
              mass="0.05" euler="90 0 0" material="grid"/>
        <joint name="right_front_joint" type="hinge" axis="0 1 0" damping="0.01"/>
      </body>
      
      <body name="right_mid_wheel" pos="0 -0.36 0">
        <geom name="rm_wheel" type="cylinder" size="0.1 0.05" rgba="0.5 0.5 0.5 1" 
              mass="0.05" euler="90 0 0" material="grid"/>
        <joint name="right_mid_joint" type="hinge" axis="0 1 0" damping="0.01"/>
      </body>
      
      <body name="right_rear_wheel" pos="-0.25 -0.36 0">
        <geom name="rr_wheel" type="cylinder" size="0.1 0.05" rgba="0.5 0.5 0.5 1" 
              mass="0.05" euler="90 0 0" material="grid"/>
        <joint name="right_rear_joint" type="hinge" axis="0 1 0" damping="0.01"/>
      </body>
    </body>
  </worldbody>

  <contact>
    <pair geom2="floor" geom1="lf_wheel" condim="3" friction="0.1 1"/>
    <pair geom2="floor" geom1="lm_wheel" condim="3" friction="0.1 1"/>
    <pair geom2="floor" geom1="lr_wheel" condim="3" friction="0.1 1"/>
    <pair geom2="floor" geom1="rf_wheel" condim="3" friction="0.1 1"/>
    <pair geom2="floor" geom1="rm_wheel" condim="3" friction="0.1 1"/>
    <pair geom2="floor" geom1="rr_wheel" condim="3" friction="0.1 1"/>
  </contact>
    
  <actuator>
    <motor name="left_front_motor" joint="left_front_joint" gear="50" ctrllimited="false" ctrlrange="-2.1 2.1"/>
    <motor name="left_mid_motor" joint="left_mid_joint" gear="50" ctrllimited="false" ctrlrange="-2.1 2.1"/>
    <motor name="left_rear_motor" joint="left_rear_joint" gear="50" ctrllimited="false" ctrlrange="-2.1 2.1"/>

    <motor name="right_front_motor" joint="right_front_joint" gear="50" ctrllimited="false" ctrlrange="-2.1 2.1"/>
    <motor name="right_mid_motor" joint="right_mid_joint" gear="50" ctrllimited="false" ctrlrange="-2.1 2.1"/>
    <motor name="right_rear_motor" joint="right_rear_joint" gear="50" ctrllimited="false" ctrlrange="-2.1 2.1"/>
  </actuator>
</mujoco>

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Anisotropic friction simulation for differential drive #2926

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Anisotropic friction simulation for differential drive #2926

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ThreeTNT Nov 4, 2025

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 0 comments

ThreeTNT
Nov 4, 2025