Difference in Simulation Results Between Mujoco and Genesis #837
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I can reproduce it, and I am looking into it. |
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I don’t think it is enough to explain the discrepency but I doubt Genesis is able to deal with the robot joint of Walker at the moment (I’m already looking into this particular issue): <joint name="rootz" axis="0 0 1" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rootx" axis="1 0 0" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rooty" axis="0 1 0" type="hinge" limited="false" armature="0" damping="0"/> |
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For the record, here are the MJCF file and script I'm using for debugging this problem: <mujoco model="planar walker">
<asset>
<texture name="grid" type="2d" builtin="checker" rgb1=".1 .2 .3" rgb2=".2 .3 .4" width="300" height="300" mark="edge" markrgb=".2 .3 .4"/>
<material name="grid" texture="grid" texrepeat="1 1" texuniform="true" reflectance=".2"/>
<material name="self" rgba=".7 .5 .3 1"/>
<material name="site" rgba=".5 .5 .5 .3"/>
</asset>
<option timestep="0.005" iterations="2" ls_iterations="5">
<flag eulerdamp="disable"/>
</option>
<custom>
<numeric data="4" name="max_contact_points"/>
<numeric data="4" name="max_geom_pairs"/>
</custom>
<statistic extent="2" center="0 0 1"/>
<default>
<joint damping=".1" armature="0.01" limited="true" solimplimit="0 .99 .01"/>
<geom contype="1" conaffinity="0" friction=".7 .1 .1"/>
<motor ctrlrange="-1 1" ctrllimited="true"/>
<site size="0.01"/>
<default class="walker">
<geom material="self" type="capsule"/>
<joint axis="0 -1 0"/>
</default>
</default>
<worldbody>
<geom name="floor" type="plane" conaffinity="1" pos="248 0 0" size="250 .8 .2" material="grid" zaxis="0 0 1"/>
<body name="torso" pos="0 0 1.3" childclass="walker">
<light name="light" pos="0 0 2" mode="trackcom"/>
<camera name="side" pos="0 -2 .7" euler="60 0 0" mode="trackcom"/>
<camera name="back" pos="-2 0 .5" xyaxes="0 -1 0 1 0 3" mode="trackcom"/>
<joint name="rootz" axis="0 0 1" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rootx" axis="1 0 0" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rooty" axis="0 1 0" type="hinge" limited="false" armature="0" damping="0"/>
<geom name="torso" size="0.07 0.3"/>
<body name="right_thigh" pos="0 -.05 -0.3">
<joint name="right_hip" range="-20 100"/>
<geom name="right_thigh" pos="0 0 -0.225" size="0.05 0.225"/>
<body name="right_leg" pos="0 0 -0.7">
<joint name="right_knee" pos="0 0 0.25" range="-150 0"/>
<geom name="right_leg" size="0.04 0.25"/>
<body name="right_foot" pos="0.06 0 -0.25">
<joint name="right_ankle" pos="-0.06 0 0" range="-45 45"/>
<geom name="right_foot" zaxis="1 0 0" size="0.05 0.1"/>
</body>
</body>
</body>
<body name="left_thigh" pos="0 .05 -0.3" >
<joint name="left_hip" range="-20 100"/>
<geom name="left_thigh" pos="0 0 -0.225" size="0.05 0.225"/>
<body name="left_leg" pos="0 0 -0.7">
<joint name="left_knee" pos="0 0 0.25" range="-150 0"/>
<geom name="left_leg" size="0.04 0.25"/>
<body name="left_foot" pos="0.06 0 -0.25">
<joint name="left_ankle" pos="-0.06 0 0" range="-45 45"/>
<geom name="left_foot" zaxis="1 0 0" size="0.05 0.1"/>
</body>
</body>
</body>
</body>
</worldbody>
<sensor>
<subtreelinvel name="torso_subtreelinvel" body="torso"/>
</sensor>
<actuator>
<motor name="right_hip" joint="right_hip" gear="100"/>
<motor name="right_knee" joint="right_knee" gear="50"/>
<motor name="right_ankle" joint="right_ankle" gear="20"/>
<motor name="left_hip" joint="left_hip" gear="100"/>
<motor name="left_knee" joint="left_knee" gear="50"/>
<motor name="left_ankle" joint="left_ankle" gear="20"/>
</actuator>
</mujoco>import genesis as gs
gs.init(backend=gs.cpu)
scene = gs.Scene(
rigid_options=gs.options.RigidOptions(
dt=0.005,
),
show_viewer=True,
show_FPS=False,
)
robot = scene.add_entity(
gs.morphs.MJCF(file="/Users/alexis.duburcq/workspace/src/genesis/walker.xml"),
)
scene.build()
scene.reset()
for _ in range(500):
scene.step() |
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I can confirm this bug is triggered by chaining multiple joints. Replacing the first compound joint by <joint name="rootz_vel" axis="0 0 1" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rooty_vel" axis="0 1 0" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rootx_vel" axis="1 0 0" type="slide" limited="false" armature="0" damping="0"/>
<joint name="rootz_ang" axis="0 0 1" type="hinge" limited="false" armature="0" damping="0"/>
<joint name="rooty_ang" axis="0 1 0" type="hinge" limited="false" armature="0" damping="0"/>
<joint name="rootx_ang" axis="1 0 0" type="hinge" limited="false" armature="0" damping="0"/> |
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Fixed by #853 |
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When simulating the walker in Mujoco and Genesis, I observed a significant difference in behavior when setting all control inputs to zero.
I have visualized the simulations, and you can find the code here: Gist.
Mujoco
Genesis
Could you provide any insights into the possible causes of this behavior?
Thank you in advance for your help!
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