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Description
Intro
Hi!
I am a student and I'm using Mujoco for rigid body simulation and reinforcement learning.
My setup
Both 3.3.0 and the Jupyter notebook in https://mujoco.readthedocs.io/en/stable/python.html.
What's happening? What did you expect?
I found that when I use a large-magnitude, high-frequency driving force to actuate a joint, noticeable and abnormal slip occurs. I have read the explanation about slip in the tutorial and understand that MuJoCo does not strictly prevent it from happening. However, I am not sure whether the situation I am facing matches the description in that section, because changing solref, solimp, and impratio does not seem to help.
I would like to know how I can ensure simulation accuracy under this kind of control force setup.
Steps for reproduction
Just need to run the following Python script.
Minimal model for reproduction
<mujoco model="Test">
<option timestep="0.0001">
<flag eulerdamp="disable" contact="enable" gravity="enable"/>
</option>
<asset>
<texture type="skybox" builtin="gradient" rgb1=".3 .5 .7" rgb2="0 0 0" width="32" height="512"/>
<texture name="body" type="cube" builtin="flat" mark="cross" width="128" height="128" rgb1="0.8 0.6 0.4" rgb2="0.8 0.6 0.4" markrgb="1 1 1" random="0.01"/>
<material name="body" texture="body" texuniform="true" rgba="0.8 0.6 .4 1"/>
<texture name="grid" type="2d" builtin="checker" width="512" height="512" rgb1=".1 .2 .3" rgb2=".2 .3 .4"/>
<material name="grid" texture="grid" texrepeat="1 1" texuniform="true" reflectance=".2"/>
</asset>
<worldbody>
<light name="light" pos="-.2 0 1"/>
<geom name="ground" type="plane" pos="0 0 0" size="0 0 10" material="grid"
zaxis="0 0 1" friction="1.0"/>
<light pos="0 0 1"/>
<light pos="1 0 1"/>
<light pos="2 0 1"/>
<light pos="3 0 1"/>
<light pos="4 0 1"/>
<light pos="5 0 1"/>
<camera name="cam" pos="0.0 -1.0 1.0" xyaxes="1 0 0 0 1 1" fovy="120" />
<body name="b1" pos="0 0 0.05">
<joint name="j0" type="free"/>
<geom name="g1" type="capsule" size="0.05" fromto="-0.05 0 0 0.05 0 0" friction="1.0"/>
<body name="b2" pos="0.2 0 0">
<joint name="j1" type="hinge" axis="0 0 1" pos="-0.1 0 0" range="-70 70"/>
<geom name="g2" type="capsule" size="0.05" fromto="-0.05 0 0 0.05 0 0" friction="1.0"/>
</body>
</body>
</worldbody>
<contact>
<pair geom1="g1" geom2="ground" friction="0.01 0.01"/>
<pair geom1="g2" geom2="ground" friction="0.01 0.01"/>
<exclude body1="b1" body2="b2"/>
</contact>
<actuator>
<motor name="act1" gear="10" joint="j1"/>
</actuator>
</mujoco>Code required for reproduction
import os
import numpy as np
import mediapy as media
import mujoco
if __name__ == "__main__":
import os
mj_model = mujoco.MjModel.from_xml_string(xml)
mj_data = mujoco.MjData(mj_model)
renderer = mujoco.Renderer(mj_model)
scene_option = mujoco.MjvOption()
scene_option.flags[mujoco.mjtVisFlag.mjVIS_JOINT] = True
duration = 3 # (seconds)
framerate = 24 # (Hz)
frames = []
mujoco.mj_resetData(mj_model, mj_data)
n_step = 0
i = 0
xfrc = np.zeros_like(mj_data.xfrc_applied)
while mj_data.time < duration:
ctrl = np.array([(-1) ** (i // 1000)])
i += 1
mj_data.ctrl = ctrl
mujoco.mj_step(mj_model, mj_data)
if len(frames) < mj_data.time * framerate:
renderer.update_scene(mj_data, scene_option=scene_option)
pixels = renderer.render()
frames.append(pixels)
media.show_video(frames, fps=framerate)Confirmations
- I searched the latest documentation thoroughly before posting.
- I searched previous Issues and Discussions, I am certain this has not been raised before.