Spatial tendon has force at resting position #2198

hmz-15 · 2024-10-30T18:34:24Z

hmz-15
Oct 30, 2024

Intro

Hi!

I am a graduate student at UCLA. I'm using the spatial tendon feature in Mujoco to create robot fingers.

My setup

I observe that there exists force on the tendon at the initial q pos (the resting position) when no control signal is applied, which causes the robot finger to bend. I already disable gravity.

My question

I wonder, why would it happen or is there anything I miss? Thank you!

Minimal model and/or code that explain my question

Please find the example as below:

<mujoco model="finger_x_rotate">
    <option>
        <flag gravity="disable" />
    </option>
    <default>
        <geom type="capsule" size=".005" rgba=".9 .7 .1 1" />
        <joint axis="1 0 0" range="-180 180" limited="true" />
    </default>
    <worldbody>
        <site name="tendon_attach_0" pos="0.0 -0.05 0.02" />
        <body name="finger_link_0" pos="0 0 0">
            <joint />
            <geom fromto="0 0 0  0 0.04 0" />
            <site name="tendon_attach_1" pos="0 0.02 0.005" />
        </body>
    </worldbody>
    <tendon>
        <spatial name="tendon" width="0.002" range="0 0.3" limited="true">
            <site site="tendon_attach_0" />
            <site site="tendon_attach_1" />
        </spatial>
    </tendon>
    <actuator>
        <position tendon="tendon" gear="1" ctrllimited="true" ctrlrange="-2 0" kp="1.0" kv="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.

Answered by hmz-15

Nov 4, 2024

I found it's due to the initial default control signal is 0 - which means the target tendon length is 0.

View full answer

hmz-15 · 2024-11-04T23:27:30Z

hmz-15
Nov 4, 2024
Author

I found it's due to the initial default control signal is 0 - which means the target tendon length is 0.

0 replies

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Spatial tendon has force at resting position #2198

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Spatial tendon has force at resting position #2198

hmz-15 Oct 30, 2024

Intro

My setup

My question

Minimal model and/or code that explain my question

Confirmations

Replies: 1 comment

hmz-15 Nov 4, 2024 Author

hmz-15
Oct 30, 2024

hmz-15
Nov 4, 2024
Author