Mismatch between qvel[3:6] and gyro sensordata for the root link #2419
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IntroHi! I am a robotics engineer. My setupMuJoCo 3.2.7, ubuntu 20.04, Python My questionAs far as I know, if I want to get the angular velocity of the root link in local frame, I can either get it from qvel[3:6] or I put an gyro sensor on the root link and these two sources of data should match, but in the follow MWE, they are not. I tried on the official humanoid.xml. The default noise on sensor should be zero, so I guess the mismatch is not due to sensor noise. Thanks. Minimal model and/or code that explain my questionIf you encountered the issue in a complex model, please simplify it as much as possible (while still reproducing the issue). Model: minimal XML<!-- Copyright 2021 DeepMind Technologies Limited
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
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<mujoco model="Humanoid">
<option timestep="0.005"/>
<visual>
<map force="0.1" zfar="30"/>
<rgba haze="0.15 0.25 0.35 1"/>
<global offwidth="2560" offheight="1440" elevation="-20" azimuth="120"/>
</visual>
<statistic center="0 0 0.7"/>
<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"/>
<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>
<default>
<motor ctrlrange="-1 1" ctrllimited="true"/>
<default class="body">
<!-- geoms -->
<geom type="capsule" condim="1" friction=".7" solimp=".9 .99 .003" solref=".015 1" material="body" group="1"/>
<default class="thigh">
<geom size=".06"/>
</default>
<default class="shin">
<geom fromto="0 0 0 0 0 -.3" size=".049"/>
</default>
<default class="foot">
<geom size=".027"/>
<default class="foot1">
<geom fromto="-.07 -.01 0 .14 -.03 0"/>
</default>
<default class="foot2">
<geom fromto="-.07 .01 0 .14 .03 0"/>
</default>
</default>
<default class="arm_upper">
<geom size=".04"/>
</default>
<default class="arm_lower">
<geom size=".031"/>
</default>
<default class="hand">
<geom type="sphere" size=".04"/>
</default>
<!-- joints -->
<joint type="hinge" damping=".2" stiffness="1" armature=".01" limited="true" solimplimit="0 .99 .01"/>
<default class="joint_big">
<joint damping="5" stiffness="10"/>
<default class="hip_x">
<joint range="-30 10"/>
</default>
<default class="hip_z">
<joint range="-60 35"/>
</default>
<default class="hip_y">
<joint axis="0 1 0" range="-150 20"/>
</default>
<default class="joint_big_stiff">
<joint stiffness="20"/>
</default>
</default>
<default class="knee">
<joint pos="0 0 .02" axis="0 -1 0" range="-160 2"/>
</default>
<default class="ankle">
<joint range="-50 50"/>
<default class="ankle_y">
<joint pos="0 0 .08" axis="0 1 0" stiffness="6"/>
</default>
<default class="ankle_x">
<joint pos="0 0 .04" stiffness="3"/>
</default>
</default>
<default class="shoulder">
<joint range="-85 60"/>
</default>
<default class="elbow">
<joint range="-100 50" stiffness="0"/>
</default>
</default>
</default>
<worldbody>
<geom name="floor" size="0 0 .05" type="plane" material="grid" condim="3"/>
<light name="spotlight" mode="targetbodycom" target="torso" diffuse=".8 .8 .8" specular="0.3 0.3 0.3" pos="0 -6 4" cutoff="30"/>
<light name="top" pos="0 0 2" mode="trackcom"/>
<body name="torso" pos="0 0 1.282" childclass="body">
<camera name="back" pos="-3 0 1" xyaxes="0 -1 0 1 0 2" mode="trackcom"/>
<camera name="side" pos="0 -3 1" xyaxes="1 0 0 0 1 2" mode="trackcom"/>
<site name="imu" pos="0 0 0"/>
<freejoint name="root"/>
<geom name="torso" fromto="0 -.07 0 0 .07 0" size=".07"/>
<geom name="waist_upper" fromto="-.01 -.06 -.12 -.01 .06 -.12" size=".06"/>
<body name="head" pos="0 0 .19">
<geom name="head" type="sphere" size=".09"/>
<camera name="egocentric" pos=".09 0 0" xyaxes="0 -1 0 .1 0 1" fovy="80"/>
</body>
<body name="waist_lower" pos="-.01 0 -.26">
<geom name="waist_lower" fromto="0 -.06 0 0 .06 0" size=".06"/>
<joint name="abdomen_z" pos="0 0 .065" axis="0 0 1" range="-45 45" class="joint_big_stiff"/>
<joint name="abdomen_y" pos="0 0 .065" axis="0 1 0" range="-75 30" class="joint_big"/>
<body name="pelvis" pos="0 0 -.165">
<joint name="abdomen_x" pos="0 0 .1" axis="1 0 0" range="-35 35" class="joint_big"/>
<geom name="butt" fromto="-.02 -.07 0 -.02 .07 0" size=".09"/>
<body name="thigh_right" pos="0 -.1 -.04">
<joint name="hip_x_right" axis="1 0 0" class="hip_x"/>
<joint name="hip_z_right" axis="0 0 1" class="hip_z"/>
<joint name="hip_y_right" class="hip_y"/>
<geom name="thigh_right" fromto="0 0 0 0 .01 -.34" class="thigh"/>
<body name="shin_right" pos="0 .01 -.4">
<joint name="knee_right" class="knee"/>
<geom name="shin_right" class="shin"/>
<body name="foot_right" pos="0 0 -.39">
<joint name="ankle_y_right" class="ankle_y"/>
<joint name="ankle_x_right" class="ankle_x" axis="1 0 .5"/>
<geom name="foot1_right" class="foot1"/>
<geom name="foot2_right" class="foot2"/>
</body>
</body>
</body>
<body name="thigh_left" pos="0 .1 -.04">
<joint name="hip_x_left" axis="-1 0 0" class="hip_x"/>
<joint name="hip_z_left" axis="0 0 -1" class="hip_z"/>
<joint name="hip_y_left" class="hip_y"/>
<geom name="thigh_left" fromto="0 0 0 0 -.01 -.34" class="thigh"/>
<body name="shin_left" pos="0 -.01 -.4">
<joint name="knee_left" class="knee"/>
<geom name="shin_left" fromto="0 0 0 0 0 -.3" class="shin"/>
<body name="foot_left" pos="0 0 -.39">
<joint name="ankle_y_left" class="ankle_y"/>
<joint name="ankle_x_left" class="ankle_x" axis="-1 0 -.5"/>
<geom name="foot1_left" class="foot1"/>
<geom name="foot2_left" class="foot2"/>
</body>
</body>
</body>
</body>
</body>
<body name="upper_arm_right" pos="0 -.17 .06">
<joint name="shoulder1_right" axis="2 1 1" class="shoulder"/>
<joint name="shoulder2_right" axis="0 -1 1" class="shoulder"/>
<geom name="upper_arm_right" fromto="0 0 0 .16 -.16 -.16" class="arm_upper"/>
<body name="lower_arm_right" pos=".18 -.18 -.18">
<joint name="elbow_right" axis="0 -1 1" class="elbow"/>
<geom name="lower_arm_right" fromto=".01 .01 .01 .17 .17 .17" class="arm_lower"/>
<body name="hand_right" pos=".18 .18 .18">
<geom name="hand_right" zaxis="1 1 1" class="hand"/>
</body>
</body>
</body>
<body name="upper_arm_left" pos="0 .17 .06">
<joint name="shoulder1_left" axis="-2 1 -1" class="shoulder"/>
<joint name="shoulder2_left" axis="0 -1 -1" class="shoulder"/>
<geom name="upper_arm_left" fromto="0 0 0 .16 .16 -.16" class="arm_upper"/>
<body name="lower_arm_left" pos=".18 .18 -.18">
<joint name="elbow_left" axis="0 -1 -1" class="elbow"/>
<geom name="lower_arm_left" fromto=".01 -.01 .01 .17 -.17 .17" class="arm_lower"/>
<body name="hand_left" pos=".18 -.18 .18">
<geom name="hand_left" zaxis="1 -1 1" class="hand"/>
</body>
</body>
</body>
</body>
</worldbody>
<contact>
<exclude body1="waist_lower" body2="thigh_right"/>
<exclude body1="waist_lower" body2="thigh_left"/>
</contact>
<tendon>
<fixed name="hamstring_right" limited="true" range="-0.3 2">
<joint joint="hip_y_right" coef=".5"/>
<joint joint="knee_right" coef="-.5"/>
</fixed>
<fixed name="hamstring_left" limited="true" range="-0.3 2">
<joint joint="hip_y_left" coef=".5"/>
<joint joint="knee_left" coef="-.5"/>
</fixed>
</tendon>
<actuator>
<motor name="abdomen_z" gear="40" joint="abdomen_z"/>
<motor name="abdomen_y" gear="40" joint="abdomen_y"/>
<motor name="abdomen_x" gear="40" joint="abdomen_x"/>
<motor name="hip_x_right" gear="40" joint="hip_x_right"/>
<motor name="hip_z_right" gear="40" joint="hip_z_right"/>
<motor name="hip_y_right" gear="120" joint="hip_y_right"/>
<motor name="knee_right" gear="80" joint="knee_right"/>
<motor name="ankle_y_right" gear="20" joint="ankle_y_right"/>
<motor name="ankle_x_right" gear="20" joint="ankle_x_right"/>
<motor name="hip_x_left" gear="40" joint="hip_x_left"/>
<motor name="hip_z_left" gear="40" joint="hip_z_left"/>
<motor name="hip_y_left" gear="120" joint="hip_y_left"/>
<motor name="knee_left" gear="80" joint="knee_left"/>
<motor name="ankle_y_left" gear="20" joint="ankle_y_left"/>
<motor name="ankle_x_left" gear="20" joint="ankle_x_left"/>
<motor name="shoulder1_right" gear="20" joint="shoulder1_right"/>
<motor name="shoulder2_right" gear="20" joint="shoulder2_right"/>
<motor name="elbow_right" gear="40" joint="elbow_right"/>
<motor name="shoulder1_left" gear="20" joint="shoulder1_left"/>
<motor name="shoulder2_left" gear="20" joint="shoulder2_left"/>
<motor name="elbow_left" gear="40" joint="elbow_left"/>
</actuator>
<sensor>
<gyro site="imu" name="gyro"/>
</sensor>
<keyframe>
<!--
The values below are split into rows for readibility:
torso position
torso orientation
spinal
right leg
left leg
arms
-->
<key name="squat"
qpos="0 0 0.596
0.988015 0 0.154359 0
0 0.4 0
-0.25 -0.5 -2.5 -2.65 -0.8 0.56
-0.25 -0.5 -2.5 -2.65 -0.8 0.56
0 0 0 0 0 0"/>
<key name="stand_on_left_leg"
qpos="0 0 1.21948
0.971588 -0.179973 0.135318 -0.0729076
-0.0516 -0.202 0.23
-0.24 -0.007 -0.34 -1.76 -0.466 -0.0415
-0.08 -0.01 -0.37 -0.685 -0.35 -0.09
0.109 -0.067 -0.7 -0.05 0.12 0.16"/>
<key name="prone"
qpos="0.4 0 0.0757706
0.7325 0 0.680767 0
0 0.0729 0
0.0077 0.0019 -0.026 -0.351 -0.27 0
0.0077 0.0019 -0.026 -0.351 -0.27 0
0.56 -0.62 -1.752
0.56 -0.62 -1.752"/>
<key name="supine"
qpos="-0.4 0 0.08122
0.722788 0 -0.69107 0
0 -0.25 0
0.0182 0.0142 0.3 0.042 -0.44 -0.02
0.0182 0.0142 0.3 0.042 -0.44 -0.02
0.186 -0.73 -1.73
0.186 -0.73 -1.73"/>
</keyframe>
</mujoco>
Code: import mujoco
import mujoco.viewer
import time
robot_xml_path = "/path/to/humanoid.xml"
def run_mujoco():
print("Load model from: ", robot_xml_path)
mj_model = mujoco.MjModel.from_xml_path(robot_xml_path)
mj_data = mujoco.MjData(mj_model)
with mujoco.viewer.launch_passive(mj_model, mj_data) as viewer:
while viewer.is_running():
step_start = time.time()
print("qvel: ", mj_data.qvel[3:6])
print("sensordata:", mj_data.sensordata)
mj_data.ctrl = mj_data.ctrl * 0
mujoco.mj_step(mj_model, mj_data)
viewer.sync()
time_until_next_step = mj_model.opt.timestep - (
time.time() - step_start
)
if time_until_next_step > 0:
time.sleep(time_until_next_step)
if __name__ == "__main__":
run_mujoco()
Confirmations
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Answered by
yuvaltassa
Feb 11, 2025
Replies: 1 comment 3 replies
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Hello, I believe this is related to #2411, and that it is due to the freejoint's axes staying in the parent (the world), while the gyroscope is always relative to the local frame of the IMU site. |
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3 replies
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No, I don't think that is the reason. Free joint rotations are in the local frame too. The reason is probably the off-by-one property of mjData quantities. If you call mj_forward or compare to the previous velocities they should match. |
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Answer selected by
nopaddleboat
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Yes, that makes more sense. I forgot to mention that the two values are close. The following is the data I collected, the value of sensordata at time k matches value of qvel[3:6] at time k-1. Problem solved, thanks! qvel: [-1.35296545e-15 3.28538837e+00 1.71686984e-15] qvel: [-8.18230179e-16 3.31650907e+00 1.58673594e-15] qvel: [-6.96614560e-16 3.34563506e+00 1.46945330e-15] qvel: [-6.10043056e-16 3.37368565e+00 1.26338339e-15] qvel: [-1.81656014e-16 3.40118442e+00 8.15176063e-16] qvel: [ 2.61906017e-15 3.42842530e+00 -9.04623719e-16] qvel: [ 1.25583890e-15 3.45556535e+00 -5.23029376e-16] |
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Sorry for the bad info, thanks for correcting it! |
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No, I don't think that is the reason. Free joint rotations are in the local frame too. The reason is probably the off-by-one property of mjData quantities. If you call mj_forward or compare to the previous velocities they should match.