closed, toroidal-link chain explosion

NgChucky commented 9 months ago

Hi,

I'm a student and I'm trying to use MuJoCo for my personal projects. (currently simulating a resisted-motion system that involves roller-chain transmissions).

At the moment I'm looking for some help with simulating a chain made of toroidal links, under gravity.

I modelled the chain in blender and made sure that none of the solids overlap. I have also set convexhull attribute of the compiler tag in MJCF to false. But still, the chain "explodes".

Here's a short video clip of the occurrence of the problem in simulation: https://github.com/google-deepmind/mujoco/assets/112756087/be0414ce-fcf9-4bcf-a18c-5afeceddd139

Here is a model which explains my question: (please go to my repository for the assets.)

<mujoco>
    <compiler convexhull="false"/>
    <asset>
        <mesh name="link1" file="assets\Torus_001.obj" />
        <mesh name="link2" file="assets\Torus_002.obj" />
        <mesh name="link3" file="assets\Torus_003.obj" />
        <mesh name="link4" file="assets\Torus_004.obj" />
        <mesh name="link5" file="assets\Torus_005.obj" />
        <mesh name="link6" file="assets\Torus_006.obj" />
        <mesh name="link7" file="assets\Torus_007.obj" />
        <mesh name="link8" file="assets\Torus_008.obj" />
        <mesh name="link9" file="assets\Torus_009.obj" />
        <mesh name="link10" file="assets\Torus_010.obj" />
        <mesh name="link11" file="assets\Torus_011.obj" />
        <mesh name="link12" file="assets\Torus_012.obj" />
        <mesh name="link13" file="assets\Torus_013.obj" />
        <mesh name="link14" file="assets\Torus_014.obj" />
        <mesh name="link15" file="assets\Torus_015.obj" />
        <mesh name="link16" file="assets\Torus_016.obj" />
        <mesh name="link17" file="assets\Torus_017.obj" />
        <mesh name="link18" file="assets\Torus_018.obj" />
        <mesh name="link19" file="assets\Torus_019.obj" />
        <mesh name="link20" file="assets\Torus_020.obj" />
        <mesh name="link21" file="assets\Torus_021.obj" />
        <mesh name="link22" file="assets\Torus_022.obj" />
        <mesh name="link23" file="assets\Torus_023.obj" />
        <mesh name="link24" file="assets\Torus_024.obj" />
    </asset>
    <worldbody>
        <light diffuse="1 1 1" pos="6 -6 6" dir="-1 1 -1"/>
        <geom type="plane" pos="0 0 0" size="2 2 0.01"/>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link1"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link2"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link3"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link4"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link5"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link6"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link7"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link8"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link9"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link10"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link11"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link12"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link13"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link14"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link15"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link16"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link17"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link18"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link19"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link20"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link21"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link22"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link23"/>
        </body>
        <body>
            <joint type="free"/>
            <geom type="mesh" mesh="link24"/>
        </body>
    </worldbody>
</mujoco>

saran-t commented 9 months ago

Duplicate of #1380

NgChucky commented 9 months ago

@saran-t Hi Sir, my respects. I know you are busy, so can you give just a one-line hint at the solution?

google-deepmind / mujoco

closed, toroidal-link chain explosion #1396