strange 4-bars linkage control stability problem #2137

starimpact · 2024-10-12T09:35:31Z

starimpact
Oct 12, 2024

Intro

Hi!

I am a boy at home, I use MuJoCo for my research on robot control.

My setup

mujoco-mpc

My question

the control is unstable with thigh leg joints equipped, and stable after removing the thigh leg joints.
with thigh leg joints:

without thigh leg joints:

errors:

Minimal model and/or code that explain my question

robot xml:

<mujoco model="legwheel2_expand">
    <include file="./common/skybox.xml"/>
    <include file="./common/visual.xml"/>
    <include file="./common/materials.xml"/>
    <visual>
        <global offwidth="1920" offheight="1080" />
    </visual>
    <option gravity="0 0 -9.8" timestep="0.01" wind="0 0 0" integrator="Euler" />
    <default>
        <default class="hip">
            <!-- <joint armature="0.001" damping="1" stiffness="0" /> -->
            <!-- <joint damping="0.1" stiffness="0" armature="0.001" limited="true" solimplimit="0 .99 .01" range="-90 90" /> -->
            <!-- <joint damping=".01" stiffness="1" armature="0.1" /> -->
            <joint damping="1" stiffness="1" armature="0.001" />
        </default>
        <default class="leg">
            <joint damping="0.01" stiffness="0.01" armature="0.001" />
            <!-- <joint damping="1" stiffness="1" armature="0.001" /> -->
            <!-- <joint /> -->
        </default>
        <default class="wheel">
            <joint armature="0.01" damping="0.001" stiffness="0." frictionloss="0.01" />
        </default>
    </default>
    <worldbody>
        <geom name="floor" pos="0 0 -.001" size="10 10 .001" type="plane" material="grid"/>
        <body name="root" pos="0 0 0.090" euler="0 0 45">
            <freejoint name="root_joint" />
            <site name="root" pos="0 0 0.022" size="0.001" rgba="0 0 0 1"/>
            
            <geom size="0.032 0.0265 0.022" type="box" rgba="0 0 0.8 1" priority="1"  material="self" mass="0.2011" />
            <site name="root_rod_site1_left" pos="-0.027 0.031 0.020" size="0.001" rgba="0 0 0 1"/>
            <site name="root_rod_site1_right" pos="-0.027 -0.031 0.020" size="0.001" rgba="0 0 0 1"/>
            <body name="nose"  pos="0.03 0 0" >
                <geom name="nose" size="0.01 0.01 0.01" type="box" rgba="0 0.8 0.8 1" priority="1"  material="self" mass="0.0153" />
                <site name="nose" pos="0.01 0 0" size="0.001" rgba="1 0 0 1"/>
            </body>
            <body name="thigh_left" pos="-0.019 0.029 -0.018" euler="0 47 0" >
                <!-- <joint name="thigh_left_joint" type="hinge" pos="0 0 0.0255" axis="0 1 0" class="hip" /> -->
                <geom size="0.0025 0.002 0.0255" type="box" rgba="0 0.8 0. 0.5" priority="1"  material="self" mass="0.0095" />
                <body name="calf_left" pos="0.019 0.0045 -0.025" euler="0 -90 0">
                    <!-- <joint name="calf_left_joint" type="hinge" pos="0 0 0.0195" axis="0 1 0" class="leg" /> -->
                    <geom size="0.003 0.002 0.0315" type="box" rgba="0.8 0.8 0. 0.5"  priority="1"  material="self" mass="0.0061" />
                    <body name="rod_left" pos="0.023 -0.0045 0.040" euler="0 63 0" >
                        <joint name="rod_left_joint" type="hinge" pos="0 0 -0.0255" axis="0 1 0" class="leg" />
                        <geom size="0.001 0.002 0.0255" type="box" rgba="0 0.0 0.0 0.5" priority="1"  material="self" mass="0.0009"/>
                        <site name="root_rod_site2_left" pos="0 0 0.0255" size="0.001" rgba="0 1 0 1"/>
                    </body>
                    <body name="wheel_left" pos="0. 0.01 -0.0315" euler="90 0 0">
                        <joint name="wheel_left_joint" type="hinge" pos="0 0 0" axis="0 0 -1" class="wheel" />
                        <geom size="0.019 0.006" type="cylinder" rgba="0.8 0 0 1" priority="1" material="self" mass="0.0440" />
                        <geom size="0.001 0.01 0.001" type="box" rgba="0.8 0.8 0.8 1"  priority="1"  material="self" pos="0 0 -0.006" mass="0.0008" />
                    </body>
                </body>
            </body>
            
            <body name="thigh_right" pos="-0.019 -0.029 -0.018" euler="0 47 0" >
                <!-- <joint name="thigh_right_joint" type="hinge" pos="0 0 0.0255" axis="0 1 0" class="hip" /> -->
                <geom size="0.0025 0.002 0.0255" type="box" rgba="0 0.8 0. 0.5" priority="1"  material="self" mass="0.0095" />
                <body name="calf_right" pos="0.019 -0.0045 -0.025" euler="0 -90 0">
                    <!-- <joint name="calf_right_joint" type="hinge" pos="0 0 0.0195" axis="0 1 0" class="leg" /> -->
                    <geom size="0.003 0.002 0.0315" type="box" rgba="0.8 0.8 0. 0.5"  priority="1"  material="self" mass="0.0061" />
                    <body name="rod_right" pos="0.023 0.0045 0.040" euler="0 63 0" >
                        <joint name="rod_right_joint" type="hinge" pos="0 0 -0.0255" axis="0 1 0" class="leg" />
                        <geom size="0.001 0.002 0.0255" type="box" rgba="0 0.0 0.0 0.5" priority="1"  material="self" mass="0.0009"/>
                        <site name="root_rod_site2_right" pos="0 0 0.0255" size="0.001" rgba="0 1 0 1"/>
                    </body>
                    <body name="wheel_right" pos="0. -0.01 -0.0315" euler="90 0 0">
                        <joint name="wheel_right_joint" type="hinge" pos="0 0 0" axis="0 0 -1" class="wheel" />
                        <geom size="0.019 0.006" type="cylinder" rgba="0.8 0 0 1" priority="1" material="self" mass="0.0440" />
                        <geom size="0.001 0.01 0.001" type="box" rgba="0.8 0.8 0.8 1"  priority="1"  material="self" pos="0 0 0.006" mass="0.0008" />
                    </body>
                </body>
            </body>
        </body>
    </worldbody>
    <equality>
        <!-- <connect site1="root_rod_site1_left" site2="root_rod_site2_left" /> -->
        <!-- <connect site1="root_rod_site1_right" site2="root_rod_site2_right" /> -->
        <connect body1="root" body2="rod_left" anchor="-0.027 0.031 0.020" />
        <connect body1="root" body2="rod_right" anchor="-0.027 -0.031 0.020" />

        <!-- <weld body1="root" body2="rod_left" /> -->
        <!-- <weld body1="root" body2="rod_right" /> -->

        <!-- <joint joint1="calf_left_joint" joint2="thigh_left_joint" polycoef="0.0067 -3.9799 1.1248 9.2676 -26.2257" />
        <joint joint1="rod_left_joint" joint2="thigh_left_joint" polycoef="-0.0091 4.0234 -1.2602 -9.5258 23.8106"  />
        <joint joint1="calf_right_joint" joint2="thigh_right_joint" polycoef="0.0067 -3.9799 1.1248 9.2676 -26.2257"  />
        <joint joint1="rod_right_joint" joint2="thigh_right_joint" polycoef="-0.0091 4.0234 -1.2602 -9.5258 23.8106"  /> -->

    </equality>
    <actuator>
        <!-- <position name="thigh_left_pos" joint="thigh_left_joint" kp="10" kv="0" ctrllimited="true" ctrlrange="-0.15 0.25" /> -->
        <!-- <position name="thigh_right_pos" joint="thigh_right_joint" kp="10" kv="0" ctrllimited="true" ctrlrange="-0.15 0.25" /> -->

        <!-- <position name="thigh_left_pos" joint="thigh_left_joint" kp="1" kv="0" ctrllimited="true" ctrlrange="-1.0 1.0" /> -->
        <!-- <position name="thigh_right_pos" joint="thigh_right_joint" kp="1" kv="0" ctrllimited="true" ctrlrange="-1.0 1.0" /> -->
        
        <motor name="wheel_left_motor" joint="wheel_left_joint" gear="1.0" ctrllimited="true" ctrlrange="-1.0 1.0" />
        <motor name="wheel_right_motor" joint="wheel_right_joint" gear="1.0" ctrllimited="true" ctrlrange="-1.0 1.0" />
    </actuator>
</mujoco>

Confirmations

I searched the latest documentation thoroughly before posting.
I searched previous Issues and Discussions, I am certain this has not been raised before.

starimpact · 2024-10-13T02:42:28Z

starimpact
Oct 13, 2024
Author

when i change agent integrator from implicit to rk4(when planner is sampling), or from implicit to euler(when planner is iLQG), the control becomes stable!!! why????

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strange 4-bars linkage control stability problem #2137

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starimpact Oct 12, 2024

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 1 comment

Uh oh!

starimpact Oct 13, 2024 Author

starimpact
Oct 12, 2024

starimpact
Oct 13, 2024
Author