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How to use anisotropic friction coefficients in some body frame? #67

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vmanoj1996 opened this issue Nov 19, 2021 · 1 comment
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How to use anisotropic friction coefficients in some body frame? #67

vmanoj1996 opened this issue Nov 19, 2021 · 1 comment
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@yuvaltassa
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@vmanoj1996
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Friction section in mjcf modelling page does not convey the direction over which anisotropic friction force is exerted.

I am trying something similar to ice skating. Some experimentation reveals that it is acting along world frame's x, y axis.

Is there a way to get around this?
@saran-t saran-t added the question Request for help or information label Nov 23, 2021
@yuvaltassa
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Hi,

Anisotropic friction is tightly coupled to the specific collider used, as the collider determines the orientation of the contact frame. One usable collider for this purpose is capsule-plane, since the contact frame is always oriented along the capsule. Below is a minimal "ice skating" example:

ice_skate

<mujoco model="ice skate">
  <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>

  <worldbody>
    <geom name="floor" pos="0 0 0" size="5 5 .05" type="plane" material="grid"/>
    <body name="leg" pos="0 0 .3">
      <joint type="slide" axis="1 0 0"/>
      <joint type="slide" axis="0 1 0"/>
      <joint type="slide" axis="0 0 1"/>
      <joint type="hinge" axis="0 0 1"/>
      <light pos="0 0 2"/>
      <geom name="shin" type="box" size=".03 .02 .2"/>
      <geom name="skate" type="capsule" fromto=".02 0 -.25 .1 0 -.25" size=".02"/>
    </body>
  </worldbody>

  <contact>
    <pair name="non-isotropic" geom1="floor" geom2="skate" condim="3" friction="0.1 1"/>
  </contact>
</mujoco>

@TextZip TextZip mentioned this issue Oct 6, 2022
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@diuuuuuuuuuuuuuu diuuuuuuuuuuuuuu mentioned this issue Feb 10, 2023
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@yuvaltassa yuvaltassa mentioned this issue Mar 18, 2024
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@saran-t @yuvaltassa @vmanoj1996